The Journal of Experimental Medicine
VeriKine-HS Human IFN-Beta
  Home | Help | Feedback | Subscriptions | Archive | Search | Table of Contents

This Article
Right arrow Abstract Freely available
Right arrow Full Text (PDF, 306K)
Right arrow PPT slides of all figures
Right arrow Alert me when this article is cited
Right arrow Citation Map
Services
Right arrow Email this article
Right arrow Similar articles in this journal
Right arrow Similar articles in PubMed
Right arrow Alert me to new content in the JEM
Right arrow Download to citation manager
Citing Articles
Right arrow Citing Articles via HighWire
Right arrow Citing Articles via CrossRef
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Malissen, M.
Right arrow Articles by DiSanto, J. P.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by Malissen, M.
Right arrow Articles by DiSanto, J. P.
Social Bookmarking
 Add to CiteULike   Add to Complore   Add to Connotea   Add to Del.icio.us   Add to Digg   Add to Facebook   Add to Reddit   Add to Technorati   Add to Twitter  
What's this?
© The Rockefeller University Press, 0022-1007/1997/10/1277/ $5.00
The Journal of Experimental Medicine, Volume 186, Number 8, October 20, 1997 1277-1285


Articles

The Common Cytokine Receptor {gamma} Chain Controls Survival of {gamma}/{delta} T Cells

Marie Malissen*, Pablo Pereira{ddagger}, David J. Gerber§, Bernard Malissen*, and James P. DiSanto||

From the * Centre d'Immunologie Institut National de la Santé et de la Recherche Médicale–Centre National de la Recherche Scientifique de Marseille Luminy, Case 906, 13288 Marseille Cedex 9, France; {ddagger} Unité d'Immunologie, Centre National de la Recherche Scientifique Unité Recherche Associée 1961, Institut Pasteur, 75724 Paris, France; § Center for Cancer Research, Massachusetts Institute of Technology, 02139 Cambridge, Massachusetts; and || INSERM U429, Hôpital Necker-Enfants Malades, 75743 Paris, France


   Abstract
 Top
 Abstract
 Materials and Methods
 Results and Discussion
 References
 
We have investigated the role of common {gamma} chain ({gamma}c)-signaling pathways for the development of T cell receptor for antigen (TCR)-{gamma}/{delta} T cells. TCR-{gamma}/{delta}–bearing cells were absent from the adult thymus, spleen, and skin of {gamma}c-deficient ({gamma}c) mice, whereas small numbers of thymocytes expressing low levels of TCR-{gamma}/{delta} were detected during fetal life. Recent reports have suggested that signaling via interleukin (IL)-7 plays a major role in facilitating TCR-{gamma}/{delta} development through induction of V-J (variable-joining) rearrangements at the TCR-{gamma} locus. In contrast, we detected clearly TCR-{gamma} rearrangements in fetal thymi from {gamma}c mice (which fail to signal in response to IL-7) and reduced TCR-{gamma} rearrangements in adult {gamma}c thymi. No gross defects in TCR-{delta} or TCR-β rearrangements were observed in {gamma}c mice of any age. Introduction of productively rearranged TCR V{gamma}1 or TCR V{gamma}1/V{delta}6 transgenes onto mice bearing the {gamma}c mutation did not restore TCR-{gamma}/{delta} development to normal levels suggesting that {gamma}c-dependent pathways provide additional signals to developing {gamma}/{delta} T cells other than for the recombination process. Bcl-2 levels in transgenic thymocytes from {gamma}c mice were dramatically reduced compared to {gamma}c+ transgenic littermates. We favor the concept that {gamma}c-dependent receptors are required for the maintenance of TCR-{gamma}/{delta} cells and contribute to the completion of TCR-{gamma} rearrangements primarily by promoting survival of cells committed to the TCR-{gamma}/{delta} lineage.


Address correspondence to James P. DiSanto, INSERM U429, Pavillon Kirmisson, Hôpital Necker-Enfants Malades, 149 rue de Sèvres, Paris F-75743 France. Phone: 33-1-44-49-50-51; FAX: 33-1-45-75-13-02; E-mail: disanto{at}necker.fr

Tcells can be divided into two populations based on the structure of their TCRs. Most T cells express TCR heterodimers consisting of {alpha} and β chains, whereas a smaller population expresses an alternative TCR made of {gamma} and {delta} chains. These two T cell populations share a number of features, including rearranging antigen receptor chains, the products of which associate with a set of invariant CD3 polypeptides responsible for signaling to the cell that the TCR heterodimer has been engaged (for review see reference 1). In contrast, {gamma}/{delta} T cells differ from {alpha}/β T cells in their ontogeny, variable (V)1 gene repertoires, and ultimate anatomical locations (for reviews see references 2 and 3). {gamma}/{delta} T cells are the first TCR-expressing cells detected in the early fetal thymus, and persist in the adult thymus in small numbers. The first two waves of {gamma}/{delta} T cells to appear during a fetal development express V{gamma}5-joining {gamma}1 (J{gamma}1) and V{gamma}6-J{gamma}1 genes, both of which pair with {delta} chains composed of V{delta}1-D{delta}1-J{delta}2 segment combinations. The most striking feature of these TCR-{gamma}/{delta} genes is their lack of junctional diversity (2, 3). The V{gamma}5-expressing cells migrate to the skin to become the Thy1+ dendritic epidermal T cell (DETC) population, whereas V{gamma}6-expressing cells migrate to mucosal surfaces lining the reproductive tract and tongue (4). The production of V{gamma}5/V{delta}1 and V{gamma}6/ V{delta}1 cells slows at the end of fetal life and another wave of TCR-{gamma}/{delta} cells develops from this time onwards, which uses mainly V{gamma}4 and V{gamma}1 gene segments paired with a variety of V{delta} genes and which displays extensive junctional diversity. In the adult, these {gamma}/{delta} T cells constitute ~0.2% of the thymus and following export, seed the spleen and lymph nodes. The mechanisms that control the sequential appearance of {gamma}/{delta} T cell subsets with distinct V gene segment usage, V(D)J junctional diversity, and unique homing properties are unknown (5, 6). Recent evidence suggests that the observed TCR-{gamma} and TCR-{delta} gene rearrangements are temporally programmed and do not rely on selection of a particular subset of receptors among a diverse TCR-{gamma}/{delta} combinatorial repertoire (79).

Deciphering the role played by cell–cell interactions and soluble cytokines provided by the thymic microenvironment constitutes a central question in the development of fetal versus adult {gamma}/{delta} T cells. A variety of interleukins have been demonstrated to affect the growth and differentiation of TCR-{gamma}/{delta} cells. For instance, freshly isolated {gamma}/{delta} T cells from fetal thymus, skin, spleen, or peritoneal cavity can proliferate in vitro to IL-2, IL-7, or IL-15 (1013), and in utero administration of antibodies to the IL-2Rβ chain block development of DETC (14). Gene ablation experiments in vivo have confirmed some of these findings. Mice deficient in IL-2Rβ (shared by IL-2 and IL-15), IL-7/IL-7R{alpha}, or the common {gamma} chain ({gamma}c; shared by IL-2, IL-4, IL-7, IL-9, and IL-15) each have defects in {gamma}/{delta} T cell development (1520). Still, the mechanism by which cytokine depletion affects the differentiation program of these cells is not completely understood. Cytokines could play a role in survival or proliferation of developing thymocytes, or alternatively might directly influence the TCR rearrangement process. Along these lines, experiments using mouse fetal liver cultures supplemented with IL-7 suggested that this cytokine could specifically induce the rearrangement of TCR-{gamma} chain genes (21), and recently IL-7R{alpha}–deficient mice were shown to have a selective block in TCR-{gamma} gene recombination (22). In this report, we have analyzed mice deficient in {gamma}c to clarify the role of the {gamma}c in the development of fetal and adult {gamma}/{delta} T cells. Our results demonstrate that {gamma}c-containing receptor complexes play a role for TCR-{gamma} chain rearrangements in the adult, but not the fetal thymus, and more importantly, signaling through the {gamma}c provides essential survival signals for {gamma}/{delta} T cells.


   Materials and Methods
 Top
 Abstract
 Materials and Methods
 Results and Discussion
 References
 
Mice.
Mice harboring a null mutation of the {gamma}c have been described (19), {gamma}c-deficient mice, IL-7–deficient mice (kindly provided by R. Murray, DNAX Corp, Palo Alto, CA; reference 23), recombinase-activating gene 1–deficient mice (RAG1–/–; ref. 24), and their littermate controls were maintained in specific pathogen-free conditions and used between 4 and 8 wk of age. Fetal tissues were obtained from timed-pregnant mice. Day 0 of embryonic development was considered to be the day a vaginal plug was observed.

Mice transgenic (Tg) for TCR V{gamma}1 and double Tg for TCR V{gamma}1 and TCR V{delta}6 were constructed as follows. Genomic DNA fragments containing the rearranged TCR V{gamma}1 and V{delta}6 genes were isolated from a cosmid library prepared in pWE15 using partially digested Sau 3A I DNA from the T3.13.1 TCR-{gamma}/{delta} hybridoma (25). The V{gamma}1-J{gamma}4 clone (45 kb) contained 10 kb of upstream sequence and extended 26 kb downstream of the C{gamma}4 exon. The V{delta}6-D-J{delta}1 clone (34 kb) contained 5 kb of upstream DNA and 14 kb downstream of the C{delta} exon. Tg constructs were mixed and the DNA microinjected into the pronuclei of fertilized embryos. Mice carrying the Tg TCRs were identified by PCR and backcrossed onto the C57Bl/6 background. Mice were screened using tail DNA and primers specific for the Tg V{gamma}1 TCR: forward, 5'-CCGGCAAAAAGCAAAAAAGTT-3'; and reverse, 5'-CCCATGATGTGCCTGACCAG-3'. PCR conditions were as follows: denaturation at 94°C for 20 s, annealing at 59°C for 25 s, and extension at 74°C for 25 s for 33 cycles.

Antibodies.
The following Abs were used as conjugates to either FITC, PE, or biotin: anti–TCR-β (H57-597), anti–TCR-{gamma}/{delta} (GL3), anti-TCR V{gamma}5 (536), anti-CD3 (2C11), anti-CD4, anti-CD8{alpha}, anti-CD24 (J11d), anti–Mac-1 (M1/70), and anti-CD32 (2.4G2). Streptavidin Tricolor (CALTAG Labs., South San Francisco, CA) was used to detect biotinylated antibodies. The antibody specific for TCR V{gamma}1 (2.11) has been described (25). A clonotypic antibody recognizing V{gamma}1/V{delta}6 TCR heterodimer (1.9) was obtained in the same fusion and its specificity verified using a panel of {gamma}/{delta} T cell hybridomas as described (25).

FACS® Analysis and Cell Sorting.
Single cell suspensions obtained from thymus or spleen were lysed of red cells using hypotonic NH4Cl solution. DETCs were isolated from ear skin using trypsinization and mechanical disaggregation as described (26). Nonspecific binding of mAbs to FcRs was reduced by preincubation with anti-CD32 mAb for 15 min. For surface staining, cells were incubated with saturating amounts of directly conjugated mAbs for 20 min, washed twice, and incubated with streptavidin Tricolor. For Bcl-2 staining, surface antigens were stained as above, and cells were washed in PBS and fixed in PBS containing 1% paraformaldehyde/0.01% Tween-20 for 90 min on ice. Cells were subsequently incubated with hamster anti–mouse Bcl-2 (clone 3F11; PharMingen, San Diego, CA) or purified hamster Ig. Cells were washed, incubated with biotinylated goat anti– hamster Ig, and finally with streptavidin Tricolor. Cells were analyzed on a FACScan® flow cytometer using CellQuest software (Becton Dickinson, Mountain View, CA). For isolation of early thymocyte precursors, cells were stained with CD4-FITC and CD8-PE, and double negative (DN) cells sorted using a FACStar Plus® cell sorter (Becton Dickinson).

PCR Analysis.
DNA samples were extracted from total or fractionated populations of fetal or adult thymocytes using the salting-out technique (27). PCR reactions were done in a final volume of 20 µl and included a maximum of 100 ng of template DNA, 1 mM of each primer, 200 µM of each deoxynucleotide triphosphate, and 0.2 U of Taq DNA polymerase. Whole reaction mixtures were run on a 1.5% agarose gel, blotted to nylon membrane (Gene Screen Plus, New England Nuclear, Boston, MA), and hybridized with 32P-labeled oligonucleotide probes.

The oligonucleotides and PCR conditions used for the analysis of TCR-β rearrangements were as described (28). For the TCR-{gamma} and TCR-{delta} rearrangements, PCR were performed essentially as described (9) except that each cycle was shortened as follows: incubation at 94°C for 30 s, annealing at 50–60°C for 30 s, and extension at 72°C for 40 s. At least two sets of independent experiments were performed for each sample. To show that there is a linear relationship between product yield and the number of input target sequences, serial dilutions have been analyzed for each DNA sample. Hybridizing bands were quantitated using a phosphorimager (BAS1000; Raytest, Courbevoie, France). Before the analysis of the relative levels of TCR gene rearrangements, the quality and quantity of DNA present in each sample were checked by amplifying the nonrearranging trithorax gene (MTrx; reference 29) using primers MTrx1: 5'-AGGGTAAGCTGTGCTATGG-3' and MTrx2: 5'-AGTAGTGTTTCCTCAGTCCCC-3'.


   Results and Discussion
 Top
 Abstract
 Materials and Methods
 Results and Discussion
 References
 
Absence of TCR-{gamma}/{delta} Cells in {gamma}c-deficient Mice.
In vitro data have suggested an important role for IL-2, IL-7, and IL-15 in the survival, proliferation, and differentiation of cells belonging to the {gamma}/{delta} T cell lineage (1013). Because the {gamma}c receptor plays an integral role in the function of these cytokine receptors, we anticipated that {gamma}c mice would exhibit a defect in {gamma}/{delta} T cell development. As most adult {gamma}/ {delta} T cells fail to express the CD4 and CD8 coreceptors and are found in the DN subset of T cells, we examined wild-type (wt) and {gamma}c DN thymocytes for the presence of cells bearing TCR-{gamma}/{delta} receptors. Compared to control mice, adult thymi from {gamma}c mice showed a complete absence of TCR-{gamma}/{delta}+ cells (Fig. 1). Further analysis of the peripheral lymphoid organs, skin, and small intestine of adult {gamma}c-deficient mice failed to demonstrate any TCR-{gamma}/{delta}+ cells in the animal (Fig. 1 and data not shown). These results confirm and extend previous observations demonstrating the strict dependence on {gamma}c-containing receptors for the development of all types of {gamma}/{delta} T cells present in adult mice (1520).


Figure 1
View larger version (19K):
[in this window]
[in a new window]
[Download PPT slide]
 
Figure 1 Flow cytometric analysis of {gamma}/{delta} T cells from adult {gamma}c+ and {gamma}c mice. (A) Thymocytes were stained with FITC–anti–pan-TCR-{gamma}/{delta} (GL3), PE–anti-CD3, biotin-anti–CD4, and biotin–anti-CD8{alpha}. CD4 CD8 (DN) cells were electronically gated. (B) Skin-resident DETCs were isolated as indicated in Materials and Methods, and stained with biotin–anti-TCR V{gamma}5 and FITC–anti-CD3. (C) Splenocytes were monocyte depleted by adherence and stained with FITC–anti–pan-TCR-{gamma}/{delta}, PE–anti-CD3, biotin–anti-CD4, and biotin–anti-CD8{alpha}. CD3+ DN cells were electronically gated. Biotinylated antibodies were revealed with streptavidin-Tricolor.

 
Considering that {gamma}/{delta} T cells constitute a minor cell population in the adult thymus, we next analyzed fetal thymi from {gamma}c mice, since they contain a higher frequency of {gamma}/ {delta} T cells (9). Total thymocyte cell numbers were clearly reduced in {gamma}c mice relative to control mice at all stages of fetal development examined (Table 1) although CD4 and CD8 expression was unaltered (data not shown). An ~10-fold reduction in cell number is apparent in {gamma}c fetal thymi, yet with age, thymocyte cell numbers increase in parallel with {gamma}c+ mice. This suggests that alternative {gamma}c-independent signaling pathways (including that of the receptor tyrosine kinase c-kit; reference 30) support continuous thymic seeding and permit progressive thymocyte accumulation. Analysis of fetal (days 16–18) {gamma}c-deficient thymocytes revealed a reduced percentage of cells expressing TCR-{gamma}/{delta} heterodimers (Fig. 2 and data not shown) and suggested that {gamma}/{delta} T cells might have some capacity to develop in that context, but might subsequently be lost, perhaps due to poor survival or failure to mature. Consistent with this hypothesis, the few fetal TCR-{gamma}/{delta} thymocytes found in {gamma}c mice have an immature phenotype characterized by low levels of TCR-{gamma}/{delta} heterodimers and high levels of heat-stable antigen (HSAhi; Fig. 2). Similar observations have been made in IL-7–deficient mice (16), pointing to IL-7 as the {gamma}c-dependent cytokine responsible for the defect observed in {gamma}c thymi.


View this table:
[in this window]
[in a new window]

 
Table 1 Cellularity of Fetal and Neonatal Thymi from {gamma}c Mice

 

Figure 2
View larger version (24K):
[in this window]
[in a new window]
[Download PPT slide]
 
Figure 2 Flow cytometric analysis of fetal thymocytes from {gamma}c+ and {gamma}c mice. (A) Thymocytes were stained with FITC–anti–pan-TCR-{gamma}/{delta} and PE–anti-CD3. (B) Thymocytes were stained with FITC–anti-pan-TCR-{gamma}/{delta} and PE–anti-HSA. In all experiments, nonspecific binding was blocked by the addition of anti-CD16/32.

 
Taken together, these observations confirm the major role played by the IL-7/{gamma}c–signaling pathway in {gamma}/{delta} T cell development (1620), but also suggest that factors independent of {gamma}c and IL-7 are present in the fetal, but not the adult, thymus and can support the appearance of the most immature {gamma}/{delta} T cells. Recently, a novel cytokine, thymic stromal cell–derived lymphopoeitin (TSLP; reference 31), has been identified which shares biological activities with IL-7 and uses the IL-7R{alpha} chain for signaling (32). We would hypothesize that TSLP could partially replace IL-7 during fetal development in {gamma}c mice. Two additional observations support this view. First, thymocytes from {gamma}c mice respond to TSLP (33) and second, mice with a deletion of the IL-7R{alpha} chain have neither fetal nor adult TCR-{gamma}/{delta} cells detectable by FACS® analysis (17). Therefore, the spectrum of cytokine receptors expressed by fetal and adult immature thymocytes may be identical, but fetal versus adult thymic stroma may differ in their abilities to produce cytokines, like TSLP. Along this line, it will be interesting to determine the relative expression of TSLP in fetal and adult thymi.

TCR Rearrangements in {gamma}c Thymocytes.
We considered a number of nonexclusive hypotheses to explain the pronounced negative effect of {gamma}c deficiency on {gamma}/{delta} T cell development: (a) {gamma}c may be required for committment to the TCR-{gamma}/{delta} lineage (defect in {alpha}/β–{gamma}/{delta} lineage branching), (b) {gamma}c may be required for initiation or completion of the site-specific DNA recombination process affecting the TCR-{gamma} and/or TCR-{delta} loci (defect in TCR rearrangements), or (c) signals via {gamma}c may be essential for the survival of cells during the process of {gamma}/{delta} T cell differentiation.

To explore these different possibilities, we analyzed the status of TCR gene rearrangements in fetal and adult thymocytes from wt and {gamma}c-deficient mice using a polymerase chain reaction technique that can specifically assess the presence of rearranged DNA from the various TCR gene loci (9, 28). The results shown in Fig. 3 were generated using fetal (day 17) thymocytes and PCR primer pairs specific for the V{gamma}5-J{gamma}1, V{gamma}1-J{gamma}4, V{delta}1-J{delta}2, and V{delta}4-J{delta}1 rearrangements. Although V{delta}4-J{delta}1 and V{gamma}1-J{gamma}4 rearrangements were nearly unaffected in {gamma}c fetal thymi, the canonical V{delta}1-J{delta}2 and V{gamma}5-J{gamma}1 rearrangements found in thymocytes destined to seed the skin epithelium (4) were clearly reduced (Fig. 3). As expected from the fact that the {gamma}c mutation does not block the development of {alpha}/β T cells (19, 20), DNA samples from {gamma}c thymi contained Dβ-Jβ and Vβ-Dβ-Jβ rearrangements that were as diverse as those found in wt samples (data not shown).


Figure 3
Figure 3
View larger version (52K):
[in this window]
[in a new window]
[Download PPT slide]
 
Figure 3 Quantitation of TCR-{delta} and TCR-{gamma} rearrangements in fetal {gamma}c+ and {gamma}c thymocytes. (A) Indicated rearrangements were amplified from DNA isolated from unfractionated D17 fetal {gamma}c+ or {gamma}c thymi. Serial dilutions of DNA template were analyzed (1x, 2x, 4x, and 8x). (B) Quantification of A. Hybridizing bands were scanned using a phosphorimager and the relative levels of rearrangements compared to wild-type (WT) {gamma}c+ thymi after normalizing for input DNA using MTrx primers. See Materials and Methods for details.

 
Similar studies were performed on adult {gamma}c thymi. As shown in Fig. 4, the V{gamma}1-J{gamma}4 rearrangements detected in 4-wk-old {gamma}c thymi represent 23% of those observed in wt thymi, respectively. Only limited V{gamma}4-J{gamma}1 rearrangements are observed in adult {gamma}c thymi, representing ~1% of the levels observed in adult wt thymi. In contrast, the extent of TCR-{delta} rearrangements found in adult thymi from {gamma}c-mutant mice resembled those present in wt adult thymi (Fig. 4 B, top). Thus, these results suggest that the {gamma}c mutation has little effect on adult TCR-{delta} rearrangements, but appears to selectively reduce adult TCR-{gamma} rearrangements. Parallel studies using IL-7–deficient mice demonstrated a similar defect in TCR-{gamma} rearrangements (Table 2).


Figure 4
Figure 4
View larger version (34K):
[in this window]
[in a new window]
[Download PPT slide]
 
Figure 4 Quantitation of TCR-{delta} and TCR-{gamma} rearrangements in adult {gamma}c+ and {gamma}c thymocytes. (A) Rearrangements of V{delta}4-J{delta}1 and V{gamma}1-J{gamma}4 were amplified from DNA isolated from unfractionated {gamma}c+ or {gamma}c thymi. Serial dilutions of DNA template were analyzed (1x, 2x, and 4x). (B) Quantification of A. Relative levels of rearrangements are compared to wild-type (WT) {gamma}c+ thymi.

 

View this table:
[in this window]
[in a new window]

 
Table 2 TCR-{gamma} and TCR-{delta} Rearrangements in {gamma}c and IL-7–/– Thymi

 
Most developing {alpha}/β T cells contain TCR-{delta} gene segments that have rearranged during the DN stages of development (34, 35). As a result, TCR-{alpha}+ thymocytes retain TCR-{delta} locus sequences (3638), which could account for the split phenotype observed for the TCR-{gamma} and TCR-{delta} loci in unfractionated adult {gamma}c thymocytes (Fig. 4). We therefore examined TCR-{delta} rearrangements in CD4CD8 precursors from {gamma}c mutant mice. As summarized in Table 3, the extent of TCR-{delta} rearrangement present in {gamma}c DN thymocytes was found to be similar to that observed in total {gamma}c thymocytes and in CD3{varepsilon}{Delta}5/{Delta}5 thymocytes, which are an enriched source of {gamma}c+ DN cells with normal levels of TCR-{delta} gene rearrangements (34). Therefore, these findings demonstrate that TCR-{delta} genes do rearrange in the CD4CD8 precursors isolated from adult {gamma}c mice. TCR-{gamma} rearrangements in {gamma}c DN thymocytes were also reduced (data not shown).


View this table:
[in this window]
[in a new window]

 
Table 3 TCR-{delta} Rearrangements from {gamma}c Thymocyte Precursors

 
In conclusion, our analysis of TCR-{gamma} and TCR-{delta} rearrangements in fetal and adult {gamma}c thymi distinguishes TCR-{gamma}/{delta} cell development during these two stages. Although noncanonical TCR-{gamma} and TCR-{delta} rearrangements were both present during the fetal period, TCR-{gamma}, but not TCR-{delta}, rearrangements were severely reduced in the adult {gamma}c thymus. The implications of these observations are the following. First, during fetal life, the absence of {gamma}c signaling pathways does not impair the ability to rearrange the TCR-{gamma} or TCR-{delta} loci. This suggests that {gamma}c-independent factors may compensate for the lack of IL-7/{gamma}c–mediated signals. Second, the fact that fetal and adult thymi from {gamma}c mice do contain TCR-{gamma} and TCR-{delta} rearrangements, but fail to give rise to mature {gamma}/{delta} T cells strongly suggests that other defects (e.g., survival of already committed or successfully rearranged {gamma}/{delta} T cells) likely accounts for the defective {gamma}/{delta} T cell development observed in {gamma}c thymi.

Lack of TCR-{gamma}/{delta} Cell Survival in {gamma}c-deficient Mice Tg for Rearranged TCR V{gamma}1 or TCR V{gamma}1/V{delta}6.
To further address potential defects in {alpha}/β–{gamma}/{delta} lineage branching and/ or {gamma}/{delta} T cell survival, we crossed {gamma}c-deficient mice with mice Tg for a functionally rearranged TCR V{gamma}1 gene or with double Tg mice harboring the same TCR V{gamma}1 and a productively rearranged TCR V{delta}6 gene. The T3.13.3 hybridoma from which these rearranged TCR chains were isolated corresponds to the subset of adult TCR-{gamma}/{delta} cells and the TCR V{gamma}1/V{delta}6 heterodimer demonstrates extensive junctional diversity (25). In addition, the V{gamma}1 Tg construct contains the necessary flanking DNA sequences to ensure proper expression in TCR-{gamma}/{delta} precursors, as well as the silencer element required to prevent its adventitious expression in TCR-{alpha}/β lineage cells (39). Founder mice expressing the V{gamma}1 or V{gamma}1/V{delta}6 constructs were identified and crossed onto the {gamma}c-deficient background.

Expression of the V{gamma}1 Tg alone in mice with or without the {gamma}c mutation did not alter absolute thymocyte cell numbers or the expression of mature CD4 or CD8 single positive thymocytes (Table 4; Fig. 5). Total thymocyte preparations from nontransgenic littermates contained only a very small percentage of cells marked with the anti-TCR V{gamma}1 antibody, whereas {gamma}c+ V{gamma}1 Tg animals demonstrate an increase in both the frequency (Fig. 5) and absolute numbers of V{gamma}1 {gamma}/{delta} T cells (Table 4). Importantly, the V{gamma}1+ cells were negative for TCR-β chains, demonstrating that the Tg was correctly expressed in TCR-{gamma}/{delta} cells and that the flanking silencer element was operative in the {alpha} T cells found in these Tg mice (Fig. 5). {gamma}c TCR-{gamma} Tg animals showed a population of V{gamma}1+ cells in total thymus preparations; these Tg+ thymocytes were more clearly demonstrated in the DN compartment (Fig. 5). Despite expression of the Tg V{gamma}1 chain, {gamma}/{delta} T cells in {gamma}c mice were still severely reduced. Compared with {gamma}c+ Tg animals, there was a 120-fold reduction in absolute numbers of V{gamma}1+ cells (Table 4). Considering that the {gamma}c chain plays a role in the generation of the earliest noncommitted thymic precursors (CD44+CD25 cells; reference 40) which are 15-fold reduced in {gamma}c mice (data not shown), part of the dramatic reduction in V{gamma}1+ thymocytes in {gamma}c Tg mice stems from the limited number of thymocyte precursors available to express the Tg V{gamma}1 receptor. Taking this into account, {gamma}/{delta} T cells are still eightfold reduced (120-fold/15-fold) in {gamma}c Tg mice relative to {gamma}c+ Tg controls, suggesting that additional mechanisms are responsible for the defective {gamma}/{delta} T cell development. Similar results were obtained using mice expressing the same TCR V{gamma}1 chain and a rearranged TCR V{delta}6 (Fig. 6 and data not shown). We conclude that a rearranged TCR-{gamma}/{delta} Tg does not restore normal {gamma}/{delta} T cell development in the absence of {gamma}c. Moreover, since {gamma}c mice can express the TCR-{gamma}/{delta} transgenes, a defect in TCR-{alpha}/ β–{gamma}/{delta} lineage branching can be effectively ruled out.


View this table:
[in this window]
[in a new window]

 
Table 4 Transgenic {gamma}/{delta} T Cell Development in {gamma}c Mice

 

Figure 5
View larger version (23K):
[in this window]
[in a new window]
[Download PPT slide]
 
Figure 5 Flow cytometric analysis of thymocytes from {gamma}c+ or {gamma}c mice transgenic for a rearranged TCR V{gamma}1 receptor. (A) Cells were stained with FITC–anti-CD8{alpha} and PE–anti-CD4. (B) Cells were stained with FITC–anti–TCR V{gamma}1 and biotin–anti–TCR-β. (C) Cells were stained with FITC–anti–TCR V{gamma}1, PE–anti-CD4, and PE–anti-CD8{alpha}. CD4CD8 (DN) cells were electronically gated.

 

Figure 6
View larger version (17K):
[in this window]
[in a new window]
[Download PPT slide]
 
Figure 6 Flow cytometric analysis of thymocytes and splenocytes of {gamma}c+ and {gamma}c mice transgenic for TCR V{gamma}1 or double transgenic for TCR V{gamma}1/V{delta}6. Cells were stained with combinations of FITC–anti–TCR V{gamma}1, FITC–anti–TCR{gamma}/{delta} clonotype, PE–anti-CD3, and PE–anti-Mac1.

 
Considering that thymically derived {gamma}/{delta} T cells seed the spleen and lymph nodes of postnatal mice, we further examined the peripheral lymphoid compartments for transgenic {gamma}/{delta} T cells. As shown in Fig. 6, a large population of cells expressing the transgenic TCR-{gamma}/{delta} receptor are present in the spleen of {gamma}c+ Tg animals; these cells coexpress CD3, but are TCR-β negative (data not shown) and accumulate to levels which are approximately six-fold higher in absolute numbers than {gamma}c+ nontransgenic animals (Table 4). In contrast, the periphery of {gamma}c Tgs contain only a few cells expressing the Tg TCR-{gamma}/{delta} receptor, and these cells fail to accumulate in the spleen. In terms of absolute numbers, {gamma}c Tg {gamma}/{delta} cells are reduced 142-fold compared with {gamma}c+ Tg littermates (Table 4). Taken together, our results suggest a major role for {gamma}c-dependent signals in the survival of {gamma}/{delta} T cells.

To investigate whether {gamma}c Tg {gamma}/{delta} T cells had a defect in survival, we examined Tg thymocytes for the expression of the antiapoptotic factor, Bcl-2. Engagement of {gamma}c-dependent receptors has been shown to maintain high levels of Bcl-2, which appear to protect lymphoid cells from cell death (4143). Although V{gamma}1+ thymocytes from {gamma}c+ mice expressed Bcl-2, Tg+ {gamma}/{delta} T cells from {gamma}c mice were essentially negative for Bcl-2 (Fig. 7). These results are consistent with a defect in {gamma}/{delta} T cell survival in the absence of {gamma}c, although the relative contribution of Bcl-2 in supporting {gamma}/{delta} T cell development remains to be determined.


Figure 7
View larger version (12K):
[in this window]
[in a new window]
[Download PPT slide]
 
Figure 7 Intracellular levels of Bcl-2 are diminished in {gamma}c {gamma}/{delta} T cells. Cells were surface stained with FITC–anti–TCR V{gamma}1, fixed, and permeabilized. Bcl-2 staining was performed as described in Materials and Methods. Dotted lines indicate staining with hamster Ig and solid lines with hamster anti–mouse Bcl-2–specific Ig.

 
Concluding Remarks.
Most {gamma}/{delta} T cells start their development within the thymus where they rearrange their TCR-{gamma} and TCR-{delta} genes via site-specific DNA recombination reactions triggered by the specialized stromal microenvironment found in the thymus. IL-2, IL-7, and IL-15 bind to specific receptors that share the {gamma}c and these cytokines have been postulated to play an important role in the survival, growth, and differentiation of {gamma}/{delta} cells (1013). In a recent study using mice deficient in IL-7R{alpha} chains, TCR-{gamma} gene rearrangements were found to be selectively abolished, and as a consequence, these mice lacked both fetal and adult TCR-{gamma}/{delta} cells (22). The authors concluded that ligands binding to the IL-7R{alpha} chain (IL-7 and TSLP) are likely to be mandatory for the process of TCR-{gamma} rearrangements within intrathymic TCR-{gamma}/{delta} cell precursors (22). Although we do not refute this conclusion, our data reveal an additional function of {gamma}c-containing receptors (likely due to IL-7), that is independent of the TCR-{gamma} rearrangement process. Thymocytes from adult {gamma}c-deficient mice do not contain detectable TCR-{gamma}/{delta} cells and showed only low levels of TCR-{gamma} rearrangements, thereby limiting the potential synthesis of TCR-{gamma} polypeptides. Complementation of such {gamma}c-deficient mice with TCR-{gamma} and TCR-{gamma}/{delta} transgenes only partially rescued thymic {gamma}/{delta} T cell development and did not permit accumulation of peripheral {gamma}/{delta} T cells. Therefore, the developmental blockade affecting the adult {gamma}/{delta} T cell lineage in {gamma}c-deficient mice results not only from the limited amounts of rearranged TCR-{gamma} genes but also from the fact that IL-7 promotes the survival of {gamma}/{delta} T cell precursors containing TCR-{gamma} and TCR-{gamma}/{delta} polypeptides. The survival role played by IL-7 in {gamma}/{delta} T cell development is supported by our observation that fetal thymocytes from {gamma}c-deficient mice do contain TCR-{gamma} and TCR-{delta} rearrangements, but fail to generate appreciable numbers of {gamma}/{delta} T cells intrathymically or to export them to the periphery. Further evidence is provided by the fact that {gamma}c {gamma}/{delta} T cells contain dramatically reduced levels of the antiapoptotic factor Bcl-2. Previous reports have shown that engagement of {gamma}c-containing receptors maintains cellular Bcl-2 protein levels (4143), thereby promoting lymphoid cell survival. Whether the near-absent Bcl-2 levels are directly responsible for the survival defect in {gamma}c {gamma}/{delta} T cells or simply an epiphenomenon related to decreased cell survival remains to be determined.

Thus, we would like to propose that for {gamma}/{delta} T cells, the primary function of {gamma}c-containing receptors is to promote survival. The ability of the {gamma}c fetal thymus to support the survival of {gamma}/{delta} T cells (possibly via TSLP) would explain the presence of TCR-{gamma} rearrangements in IL-7–deficient mice and {gamma}c-deficient mice, and their mere absence in IL-7R{alpha}–deficient mice. After successful expression of a functional TCR-{gamma}/{delta} complex, {gamma}/{delta} T cells would still require signals via {gamma}c to survive, mature, and seed the periphery. This idea gains support from the analysis of IL-7–deficient mice, where V{gamma}5loHSAhi fetal thymocytes are readily detectable, but fail to mature into V{gamma}5hiHSAlo cells (16). As a result, skin DETCs are not detectable in IL-7–deficient mice (data not shown).

Based on these results, one is led to ask why development of {alpha}/β T cells is less severely impaired in {gamma}c-deficient mice than that of {gamma}/{delta} T cells. In the {alpha}/β lineage, it has been recently documented that TCR-β rearrangements are accompanied by a selective process allowing only those cells displaying a productively rearranged Vβ gene to reach the next stage of differentiation (β selection). At a later time point, a second phase of selection, denoted TCR-{alpha}/β selection, occurs to ensure MHC restriction and self tolerance. For {gamma}/{delta} T cells, TCR-{gamma} and TCR-{delta} rearrangements are probably achieved concurrently and not subjected to pre-TCR–based epigenetic control mechanisms operating during {alpha}/β T cell development (34). In this model of {gamma}/{delta} T development, {gamma}/{delta} T cell precursors might not receive any pre-TCR or TCR signals, and engagement of {gamma}c-containing cytokine receptors may constitute the only means to support the survival of these cells. In marked contrast, in {alpha} T cell precursors, the {gamma}c-dependent survival signals and the pre-TCR dependent survival signals may partially overlap, explaining how, in the absence of survival signals dependent on {gamma}c-containing receptors, signals emanating at a latter time point from the pre-TCR may rescue the development of a few {alpha}/β T cell precursors.


   Acknowledgments
 
This work was supported by grants from the Centre National de la Recherche Scientifique, the Institut National de la Sante et de la Recherche Medicale, the Association pour le Recherche sur le Cancer, Ligue Nationale Contre le Cancer, and the Commission of the European Communities.

We thank R. Murray (DNAX Corp.) for kindly providing IL-7–deficient mice, S.Y. Huang for help in generating the TCR Tg mice, and A. Wilson, D. Guy-Grand, and F. Rieux-Laucat for helpful discussions.

Submitted: 22 April 1997
Revised: 4 August 1997


1 Abbreviations used in this paper: {gamma}c, common {gamma} chain; DETC, dendritic epidermal T cell; DN, double negative; HSA, heat-stable antigen; J, joining; RAG, recombinase-activating gene; Tg, transgenic; TSLP, thymic stromal cell–derived lymphopoeitin; V, variable; wt, wild type. Back


   References
 Top
 Abstract
 Materials and Methods
 Results and Discussion
 References
 

1 Kisielow P & von Boehmer H. Development and selection of T cells: facts and puzzles, Adv Immunol, 1995, 58, 87–209.[Medline]

2 Allison JP. {gamma}{delta} T-cell development, Curr Opin Immunol, 1993, 5, 241–246.[Medline]

3 Hass W, Pereira P & Tonegawa S. Gamma/delta cells, Annu Rev Immunol, 1993, 11, 637–685.[Medline]

4 Lafaille JJ, DeCloux A, Bonneville M, Takagaki Y & Tonegawa S. Junctional sequences of T cell receptor {gamma}{delta} genes: implications for {gamma}{delta} T cell lineages and for a novel intermediate of V-(D)-J joining, Cell, 1989, 59, 859–870.[Medline]

5 Bogue M, Mossman H, Stauffer U, Benoist C & Mathis D. The level of N-region diversity in T cell receptors is not pre-ordained in the stem cell, Eur J Immunol, 1993, 23, 1185–1188.[Medline]

6 Ikuta K, Kina T, MacNeil I, Uchida N, Peault B, Chien Y-H & Weissman IL. A developmental switch in thymic lymphocyte maturation potential occurs at the level of hematopoietic stem cells, Cell, 1990, 62, 863–874.[Medline]

7 Asarnow DM, Cado D & Raulet DH. Selection is not required to produce invariant T-cell receptor-gene junctional sequences, Nature (Lond), 1993, 362, 158–160.[Medline]

8 Gerstein RM & Lieber MR. Extent to which homology can constrain coding exon junctional diversity in V(D)J recombination, Nature (Lond), 1993, 363, 625–627.[Medline]

9 Itohara S, Monbaerts P, Iacomini J, Lafaille JJ, Nelson A, Clarke AR, Hooper ML, Farr A & Tonegawa S. T-cell receptor {delta} gene mutant mice: independent generation of {alpha}β T cells and programmed rearrangement of {gamma}{delta} TCR genes, Cell, 1993, 72, 337–345.[Medline]

10 LeClercq G, De Smedt M, Tison B & Plum J. Preferential proliferation of T cell V{gamma}3-positive cells in IL-2–stimulated fetal thymocytes, J Immunol, 1990, 145, 3992–3999.[Abstract]

11 Watanabe Y, Sudo T, Minato N, Ohnishi A & Katsura Y. Interleukin 7 preferentially supports the growth of {gamma}{delta} T cell receptor bearing T cells from fetal thymocytes in vitro. , Int Immunol, 1991, 3, 1067–1075.[Abstract/Free Full Text]

12 Matsue H, Bergstresser PR & Takashima A. Keratinocyte-derived IL-7 serves as a growth factor for dendritic epidermal T cells in mice, J Immunol, 1993, 151, 6012–6019.[Abstract]

13 Nishimura H, Hiromatsu K, Kobayashi N, Grabstein KH, Paxton R, Sugamura K, Bluestone JA & Yoshikai Y. IL-15 is a novel growth factor for murine {gamma}{delta} T cells induced by Salmonellainfection, J Immunol, 1996, 156, 663–669.[Abstract]

14 Tanaka T, Kitamura F, Nagasaka Y, Kuida K, Suwa H & Miyasaka M. Selective long-term elimination of natural killer cells in vivo by an anti-interleukin 2 receptor β chain monoclonal antibody in mice, J Exp Med, 1993, 178, 1103–1107.[Abstract/Free Full Text]

15 Suzuki H, Duncan GS, Takimoto H & Mak TW. Abnormal development of intestinal lymphocytes and peripheral natural killer cells in mice lacking the IL-2 receptor β chain, J Exp Med, 1997, 185, 499–505.[Abstract/Free Full Text]

16 Moore TA, von Freeden-Jeffry U, Murray R & Zlotnik A. Inhibition of {gamma}{delta} T cell development and early thymocyte maturation in IL-7–/– mice, J Immunol, 1996, 157, 2366–2373.[Abstract]

17 Maki S, Sunaga S, Komagata Y, Kodaira Y, Mabuchi A, Karasuyama H, Yokomuro K, Miyazaki J-I & Ikuta K. Interleukin 7 receptor–deficient mice lack {gamma}{delta} T cells, Proc Natl Acad Sci USA, 1996, 93, 7172–7177.[Abstract/Free Full Text]

18 He Y-W & Malek TR. Interleukin-7 receptor {alpha} is essential for the development of {gamma}{delta}+T cells, but not natural killer cells, J Exp Med, 1996, 184, 289–293.[Abstract/Free Full Text]

19 DiSanto JP, Müller W, Guy-Grand D, Fischer A & Rajewsky K. Lymphoid development in mice with a targeted deletion of the interleukin 2 receptor {gamma} chain, Proc Natl Acad Sci USA, 1995, 92, 377–381.[Abstract/Free Full Text]

20 Cao X, Shores EW, Hu-Li J, Anver MR, Kelsell BL, Russel SM, Drago J, Noguchi M, Grinberg A, Bloom ET et al.. Defective lymphoid development in mice lacking expression of the common cytokine receptor {gamma} chain, Immunity, 1995, 2, 223–238.[Medline]

21 Appasamy PM, Kenniston TJ, Weng Y, Holt EC, Kost J & Chambers WH. Interleukin-7–induced expression of specific T cell receptor {gamma} variable region genes in murine fetal liver cultures, J Exp Med, 1993, 178, 2201–2206.[Abstract/Free Full Text]

22 Maki K, Sunaga S & Ikuta K. The V–J recombination of T cell receptor-{gamma} genes is blocked in interleukin-7 receptor–deficient mice, J Exp Med, 1996, 184, 2423–2427.[Abstract/Free Full Text]

23 von Freeden-Jeffry U, Vieira P, Lucian LA, McNeil T, Burdach SEG & Murray R. Lymphopenia in interleukin (IL)-7 gene-deleted mice identifies IL-7 as a nonredundant cytokine, J Exp Med, 1995, 181, 1519–1526.[Abstract/Free Full Text]

24 Spanopoulou E, Roman CAJ, Cororan LM, Schlissel MS, Silver DP, Nemazee D, Nussenzweig MC, Shinton SA, Hardy RR & Baltimore D. Functional immunoglobulin transgenes guide ordered B-cell differentiation in Rag-1–deficient mice, Genes Dev, 1994, 8, 1030–1042.[Abstract/Free Full Text]

25 Pereira P, Gerber DJ, Huang SY & Tonegawa S. Ontogenic development and tissue distribution of V{gamma}1-expressing {gamma}/{delta} T lymphocytes in normal mice, J Exp Med, 1995, 182, 1921–1930.[Abstract/Free Full Text]

26 Stingl G, Gazze-Stingl LA, Aberer W & Wolff K. Antigen presentation by murine epidermal langerhans cells and its alteration by ultraviolet B light, J Immunol, 1981, 127, 1707–1713.[Medline]

27 Miller SA, Dykes DD & Polesky HF. A simple salting out procedure for extracting DNA from human nucleated cells, Nucleic Acids Res, 1988, 16, 1015.

28 Anderson SJ, Levin SD & Perlmutter RM. Protein tyrosine kinase p56lckcontrols allelic exclusion of T-cell receptor β-chain genes, Nature (Lond), 1993, 365, 552–554.[Medline]

29 Ma Q, Alder H, Nelson KK, Chatterjee D, Gu Y, Nakamura R, Canaani E, Croce CM, Siracusa LD & Buchberg AM. Analysis of the murine ALL-1 gene reveals conserved domains with human ALL-1 and identifies a motif shared with DNA methyltransferases, Proc Natl Acad Sci USA, 1993, 90, 6350–6354.[Abstract/Free Full Text]

30 Rodewald HR, Ogawa M, Haller C, Waskow W & DiSanto JP. Pro-thymocyte expansion by c-kit and the common cytokine receptor {gamma} chain is essential for repertoire formation, Immunity, 1997, 6, 265–272.[Medline]

31 Friend SL, Hosier S, Nelson A, Foxworthe D, Williams DE & Farr A. A thymic stromal cell line supports in vitro development of surface IgM+B cells and produces a novel growth factor affecting B and T lineage cells, Exp Hematol (NY), 1994, 22, 321–328.

32 Peschon JJ, Morrissey PJ, Grabstein KH, Ramsdell FJ, Maraskovsky E, Gliniak BC, Park LS, Ziegler SF, William DE, Ware CB et al.. Early lymphocyte expansion is severely impaired in interleukin 7 receptor–deficient mice, J Exp Med, 1994, 180, 1955–1960.[Abstract/Free Full Text]

33 Lantz O, Sharara LI, Tilloy F, Andersson A & DiSanto JP. Lineage relationships and differentiation of natural killer (NK) T cells: intrathymic selection and IL-4 production in the absence of NKR-P1 and Ly49 molecules, J Exp Med, 1997, 185, 1395–1401.[Abstract/Free Full Text]

34 Malissen M, Gillet A, Ardouin L, Bouvier G, Trucy J, Ferrier P, Vivier E & Malissen B. Altered T cell development in mice with a targeted mutation of the CD3{varepsilon} gene, EMBO (Eur Mol Biol Organ) J, 1995, 14, 4641–4653.[Medline]

35 Wilson A, de Villartay JP & MacDonald HR. T cell receptor {delta} gene rearrangement and T early {alpha} (TEA) expression in immature {alpha}β lineage thymocytes: implications for {alpha}β/{gamma}{delta} lineage committment, Immunity, 1996, 4, 37–45.[Medline]

36 Livak F, Petrie HT, Crispe N & Schatz DG. In-frame TCR {gamma} gene rearrangements play a critical role in the {alpha}β/{gamma}{delta} T cell lineage decision, Immunity, 1995, 2, 617–627.[Medline]

37 Nakajima PB, Menetski JP, Roth DB, Gellert M & Bosma MJ. V-D-J rearrangements at the T cell receptor {delta} locus in mouse thymocytes of the {alpha}β lineage, Immunity, 1995, 3, 609–621.[Medline]

38 Dudley EC, Girardi M, Owen MJ & Hayday AC. {alpha}β and {gamma}{delta} T cells can share a late common precursor, Curr Biol, 1995, 5, 659–669.[Medline]

39 Ishida I, Verbeck S, Bonneville M, Itohara S, Berns A & Tonegawa S. T-cell receptor {gamma}{delta} and {gamma} transgenic mice suggest a role of {gamma} gene silencer in the generation of {alpha}β T-cells, Proc Natl Acad Sci USA, 1990, 87, 3067–3071.[Abstract/Free Full Text]

40 Godfrey DI & Zlotnik A. Control points in early T-cell development, Immunol Today, 1993, 14, 547–551.[Medline]

41 Boise LH & Thompson CB. Hierarchical control of lymphocyte survival, Science (Wash DC), 1996, 274, 67–68.[Medline]

42 Boise LH, Minn AJ, June CH, Lindsten T & Thompson CB. Growth factors can enhance lymphocyte survival without committing the cell to undergo cell division, Proc Natl Acad Sci USA, 1995, 92, 5491–5495.[Abstract/Free Full Text]

43 Akbar AN, Borthwick NJ, Wickremasinghe RG, Panayiotidis P, Pilling D, Bfill M, Krajewski S, Reed JC & Salmon M. Interleukin-2 receptor common {gamma} chain signaling cytokines regulate activated T cell apoptosis in response to growth factor withdrawl: selective induction of anti-apoptotic (bcl-2, bcl-XL) but not pro-apoptotic (bax, bcl-XS) gene expression, Eur J Immunol, 1996, 26, 294–299.[Medline]


Add to CiteULike CiteULike   Add to Complore Complore   Add to Connotea Connotea   Add to Del.icio.us Del.icio.us   Add to Digg Digg   Add to Facebook Facebook   Add to Reddit Reddit   Add to Technorati Technorati   Add to Twitter Twitter    What's this?


This article has been cited by other articles:


This Article
Right arrow Abstract Freely available
Right arrow Full Text (PDF, 306K)
Right arrow PPT slides of all figures
Right arrow Alert me when this article is cited
Right arrow Citation Map
Services
Right arrow Email this article
Right arrow Similar articles in this journal
Right arrow Similar articles in PubMed
Right arrow Alert me to new content in the JEM
Right arrow Download to citation manager
Citing Articles
Right arrow Citing Articles via HighWire
Right arrow Citing Articles via CrossRef
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Malissen, M.
Right arrow Articles by DiSanto, J. P.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by Malissen, M.
Right arrow Articles by DiSanto, J. P.
Social Bookmarking
 Add to CiteULike   Add to Complore   Add to Connotea   Add to Del.icio.us   Add to Digg   Add to Facebook   Add to Reddit   Add to Technorati   Add to Twitter  
What's this?


  Home | Help | Feedback | Subscriptions | Archive | Search
TABLE OF CONTENTS