While the molecular basis underlying Th1 and Th2 differentiation still remains to be fully elucidated, recent work has demonstrated that during the commitment of naive cells to either pathway, distinct molecular events occur that result in differential gene expression. In this respect, the transcription factors c-maf 1 and GATA-3 23 have recently been shown to be induced in Th2 cells and demonstrated to play an important role in Th2 cytokine secretion. Moreover, GATA-3 not only appears to directly regulate Th2 phenotype differentiation, but also functions to inhibit commitment to the Th1 phenotype by inhibiting IFN-
secretion and the acquisition of the β2 subunit of the IL-12 receptor 4. However, overexpression of GATA-3 in differentiated effector populations has minimal effects on IL-4 or IFN-
secretion 4, suggesting that other as yet unidentified factors regulate Th2 cytokine production from effector cells.
More recently, several transmembrane receptors have been shown to be differentially expressed on Th subsets. The CC chemokine receptors (CCR)1 CCR3 and CCR4 are expressed on Th2 cells, whereas CCR1 and CCR5 are expressed on Th1 effector populations 56, providing an attractive mechanism by which Th subsets are preferentially recruited to distinct inflammatory sites. In addition to chemokine receptors, two members of the IL-1 receptor superfamily, IL-1Rrp (7; subsequently identified as the IL-18 receptor 8) and T1/ST2 9, have also been shown to be differentially expressed on Th cells. The IL-18 receptor is expressed on activated Th1 cells and regulates IFN-
secretion, IL-12R β2 expression, and Th1-mediated inflammation in vivo 10. T1/ST2, originally identified as a gene induced by serum stimulation of fibroblasts 9, has more recently been demonstrated to be overexpressed on Th2 effector cells 1112 although its function still remains unclear.
In this report, we provide evidence to suggest that T1/ST2 is more than a stable marker on the surface of Th2 cells, and demonstrate that T1/ST2 is a crucial cell surface receptor that is required for Th2 effector responses. These data suggest that T1/ST2, like other members of the IL-1 receptor superfamily including human Toll (hToll, Toll-like receptor [TLR]-4), TLR-2, and the IL-18 receptor, are critical regulators of both innate and adaptive immunity 10131415.
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Materials and Methods
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Generation of T1/ST2-Ig and T1/ST2 mAbs.
A DNA sequence containing the extracellular domain of T1/ST2 was PCR amplified and cloned into an expression vector containing the CD5 signal sequence and the hIgG1 constant region. COS cells were transiently transfected with T1/ST2-Ig cDNA, and the recombinant proteins were purified via affinity chromatography (protein A). The purity of T1/ST2-Ig was subsequently assessed by Coomassie-stained SDS-PAGE and determined to be >90%. The identify of the T1/ST2-Ig was further confirmed by mass spectrometry by comparing the trypsin peptides generated from the extracted gel band with a theoretical trypsin digest (peptide mass fingerprinting by matrix-associated laser desorption ionization time-of-flight [MALDI-TOF] analysis). We also PCR amplified a DNA sequence containing the extracellular domain of a novel Ig superfamily member identified in a murine brain cDNA library unique to a Millennium Proprietary Database. This gene, termed H1, was cloned into the identical vector as T1/ST2 containing the CD5 signal sequence. H1-Ig failed to bind to either T, B, or dendritic cells and unlike T1/ST2, was not detectable by PCR analysis in resting or activated Th1 or Th2 cells (data not shown); therefore, we used H1-Ig as an irrelevant control reagent in some experiments. The rat anti-T1/ST2 mAb (clone 3E10) was generated and characterized as described elsewhere 12.
Surface Expression of T1/ST2 on Th1 and Th2 Effector Cells.
Mice expressing the transgene for the DO11.10
/β-TCR, which recognizes residues 323–339 of chicken OVA in association with I-Ad, were provided by Dr. D. Loh (Washington University, St. Louis, MO 16). Naive TCR transgenic CD4+ T cells were isolated as described 12 and cultured in complete RPMI 1640 with OVA323–339 (10 µg/ml) and mitomycin C–treated splenocytes in a 1:5 ratio. For Th1 phenotype development, recombinant murine IL-12 (10 ng/ml) and neutralizing anti–IL-4 mAb (11B11, 40 µg/ml; R&D Systems) were added, and for Th2 development, recombinant murine IL-4 (10 ng/ml) and neutralizing polyclonal anti–murine IL-12 (TOSH-2, 3 µg/ml; Endogen) were used. After 5–7 d, cells were washed and restimulated up to three times under identical polarizing conditions. Cells were stained after 5–7 d with digoxigenin-labeled 3E10, and the number of T1/ST2-positive cells was detected by antidigoxigenin Fab fragments (Boehringer Mannheim) conjugated to PE. Expression of T1/ST2 was analyzed on a FACSCaliburTM (Becton Dickinson). To determine the cytokine profile at each time point, cells were washed and a viable CD4 population was isolated over a ficoll gradient and activated (2 x 105/well) in a 96-well plate for 24 h using plate-bound CD3 (2C11, 10 µg/ml; PharMingen). IL-4 and IFN-
levels were measured in the supernatant by ELISA (Endogen).
In Vitro Differentiation of Effector Cells in an Accessory Cell–dependent System.
CD4+ T cells from DO11.10
/β-TCR mice were activated as described above in the absence of exogenous cytokines (termed neutral conditions) or in the presence of IL-12 or IL-4, together with T1/ST2-Ig (100 µg/ml) or hIg as the appropriate isotype control. Cells were washed and replated in 96-well plates (5 x 104/well) together with 105 splenocytes/well and restimulated with OVA peptide, and cytokines were measured 48 h later. To determine the effect of T1/ST2-Ig in effector cells, Th1 and Th2 cells were reactivated with OVA peptide in the presence of either hIg or T1/ST2-Ig. In some experiments, H1-Ig was used as a second control reagent for the specificity of T1/ST2-Ig.
In Vivo Measurement of Th1- or Th2-mediated Immune Responses.
Recipient normal BALB/c mice were injected intravenously with 2 x 106 Th1 or Th2 effector cells. 24 h later, mice were exposed to an aerosol of OVA (50 mg/ml) for 20 min on two consecutive days. 1 h before allergen exposure, mice were injected intravenously with either 20 or 100 µg of mAb against T1/ST2 or 100 µg of rat IgG1. 24 h later, the trachea was cannulated, a bronchoalveolar lavage (BAL) was performed as described 17, and cytokine levels in the lavage fluid were measured by ELISA. A second series of experiments was also performed using T1/ST2-Ig (100 µg i.v.) or hIg as the appropriate isotype control. Cytospin preparations were prepared (Shandon), stained with Giemsa reagent, and a total of 200 cells were counted differentially. Lungs were then removed, inflated with 10% neutral buffered formalin, and paraffin embedded. 4-µm sections were stained for cyanide-resistant peroxidase and counterstained with hematoxylin using standard techniques. Airway inflammation was determined by semiquantitative scoring using an arbitrary system where a score of +1 represents one small focus of cells and +5 indicates widespread infiltrates. All scoring was performed by an investigator (C. Lloyd) unaware of the treatment.
Measurement of Airway Hyperresponsiveness.
Airway responsiveness was measured in Th2 recipient mice 24 h after the last aerosol challenge by recording respiratory pressure curves by whole body plethysmography (Buxco; EMKA Technologies) in response to inhaled methacholine (Sigma Chemical Co.) at concentrations of 2.5–20 mg/ml for 1 min. Airway responsiveness was expressed in enhanced pause (Penh), a calculated value, which correlates with measurement of airway resistance, impedance, and intrapleural pressure in the same mouse: Penh = (te/tr1) x Pef/Pif (te = expiration time, tr = relaxation time, Pef = peak expiratory flow, Pif = peak inspiratory flow) 18.
Active Immunization Protocol and IgE Measurement.
Male BALB/c mice (15–20 g) were immunized intraperitoneally with 7.5 µg of OVA and 1.5 mg AI(OH)3 in saline on days 0 and 7. On days 14 and 21, the mice were challenged with aerosolized OVA (10 mg/ml) for 1 h. Control mice were challenged with PBS instead of OVA. 1 h before antigen sensitization and challenge, the mice were injected with 100 µg of mAb against T1/ST2 or 100 µg of rat IgG1. 24 h after the second challenge, a BAL was performed and IL-5 levels in the BAL fluid were measured. Serum OVA-specific IgE was determined by specific ELISA.
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Results and Discussion
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T1/ST2 Is Expressed on Th2, but Not Th1 Cells.
The percentage of T1/ST2-positive cells increased under Th2 polarizing conditions from 5.2% after primary restimulation to 41% after tertiary restimulation (Fig. 1), and correlated with an enhanced capacity of cells to secrete IL-4 upon restimulation (data not shown). Naive cells and Th1 effector cells fail to express T1/ST2. These results extend our previous observations that the majority of IL-4– and IL-5–producing cells either under bulk culture conditions 12 or ex vivo from Th2-dominated immune responses 19 are contained within the T1/ST2-positive cell populations. Taken together, these data suggest that T1/ST2 is a useful surface marker for identifying IL-4– and IL-5–producing cells in vitro and in vivo.
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