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Original Article |
ckelly{at}ucsd.edu
| Abstract |
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receptor (TNFR1) and interferon
. Groups of nontreated and CFA-preimmunized male C57BL/6J or C57BL/6NOS2–/– mice were immunized with myelin oligodendrocyte glycoprotein (MOG) peptide 35–55 in CFA to induce experimental allergic encephalomyelitis (EAE). Wild-type C57BL/6J mice were protected from the development of symptoms of EAE, while the NOS2–/– mice failed to be protected. NOS2-dependent effects of CFA included an augmentation of the MOG-specific IgG1 response, a decrease in interleukin 6 production by MOG-reactive lymphocytes, and a marked decrease in mononuclear cell infiltrates in the central nervous system. These studies support the hypothesis that CFA immunization modulates immune responses through a nitric oxide–dependent mechanism.
Key Words: experimental allergic encephalomyelitis Freund's adjuvant immunosuppression interleukin 6 tumor necrosis factor 
Much of our current understanding of the CFA effect is derived from rodent models of spontaneous autoimmune diabetes mellitus. A single injection of CFA into nonobese diabetic (NOD) mice between the ages of 4 and 12 wk prevents the development of clinical diabetes indefinitely and extends NOD life span significantly 91011. CFA immunization of recipient NOD mice blocks the ability of diabetogenic T cells to transfer disease 9. Treatment of NOD mice with CFA at the time of islet cell transplantation blocks rejection and promotes the functional survival of the graft 1213. CFA did not result in a generalized state of immunosuppression, as evidenced by the ability of the recipient to reject an allograft 121314.
Cotransfer of diabetogenic T cell clones with splenocytes from a CFA-treated mouse blocks the adoptive transfer of disease 9. T cell or CD4+ cell depletion in the CFA-treated spleen eliminates the inhibitory effect 9. Enrichment of the CFA treated splenocytes for Mac-1+ cells abrogates the ability of splenocytes from a diabetic mouse to cause disease in a prediabetic NOD mouse 15. These findings may reflect a dual requirement for both T cells and macrophages in mediating adjuvant immunotherapy. Concomitant treatment of BioBreeding rats with CFA and anti–TNF-
Nitric oxide (NO) generated through the cytokine-inducible pathway has been increasingly recognized to play an important role in immune regulation in models of autoimmune disease and T cell tolerance 1718192021. Immune responses induced with Ag in CFA are markedly augmented in the presence of inducible NO synthase (NOS2) inhibitors or when using NOS2–/– mice. In this study, we examined whether functional NOS2 was required for the protective effect of CFA.
Reagents.
CFA Pretreatment and Experimental Allergic Encephalomyelitis Induction.
CFA Treatment to Induce NOS2 Expression.
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Introduction
Top
Abstract
Introduction
Materials and Methods
Results and Discussion
References
Exposure to CFA can impair the subsequent expression of autoimmune disease in small rodents. This observation, also referred to as "adjuvant immunotherapy," was first described over 40 years ago and found to be dependent on the presence of Mycobacterium tuberculosis within the adjuvant 1. This immunoprotective effect of CFA has been subsequently demonstrated in multiple autoimmune disease models, both spontaneous and induced, and in multiple species, including rats 2345, mice 6, and guinea pigs 178. In each case, preimmunization with CFA alone 21–40 d before attempted disease induction by immunization resulted in a decreased incidence and severity of disease 12378.
antibody eliminates the inhibitory effect of CFA, suggesting that TNF-
is a required mediator 16.
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Materials and Methods
Top
Abstract
Introduction
Materials and Methods
Results and Discussion
References
Experimental Animals.
Male C57BL/6, C57BL/6NOS2–/–, C57BL/6IFN-
2/–, and C57BL/6TNFR1–/– mice were obtained from The Jackson Laboratory. The mice were used between 4 and 6 wk of age. Mice were housed and handled in accordance with Veteran's Affairs and National Institutes of Health guidelines under Institutional Animal Care and Use Committee–approved protocols.
Myelin oligodendrocyte glycoprotein (MOG) peptide 35–55 N-MEVGWYRSPFSRVVHLYRNGK-C was prepared by custom solid phase synthesis (Research Genetics). IFA and Mycobacterium tuberculosis H37RA was obtained from Difco Labs. Purified pertussis toxin was obtained from List Biochemicals.
Mice to be evaluated for CFA-mediated protection were immunized i.p. 28 d before pMOG35–55 immunization with 100 µl of CFA (prepared as 0.5 mg/ml M. tuberculosis H37RA in a 1:1 (vol/vol) emulsion of Freund's adjuvant and PBS). To induce experimental allergic encephalomyelitis (EAE), mice were immunized s.c. with 300 µg of pMOG35–55 and 400 µg of M. tuberculosis H37RA in 200 µl of Freund's adjuvant. Additionally, mice were injected i.p. with 500 ng of pertussis toxin in 50 µl of PBS at the time of pMOG35–55 immunization and 48 h later. Mice were evaluated daily for signs of disease. The clinical course of the EAE was scored according to the severity as follows: 0 = no obvious signs of disease, 0.5 = partial tail weakness, 1 = limp tail, 1.5 = limp tail and hindlimb weakness, 2 = limp tail and impairment in righting reflex, 2.5 = limp tail and hindlimb paresis, 3 = bilateral hindlimb paralysis, 3.5 = bilateral hindlimb paralysis and forelimb paresis, 4 = moribund, and 5 = dead. The mice were followed for a total of 28 d, at which point the mice were killed. The brains and spinal cords were prepared for histologic evaluation by careful dissection and fixation in 10% neutral buffered formalin.
Mice were immunized s.c. at the base of the tail with CFA. At the indicated day (see Fig. 1 legend) after CFA immunization, the mice were killed, and draining lymph nodes, spleen, liver, and kidney were harvested. Of these tissues, half was flash frozen in liquid N2, and total RNA was prepared from the remaining half.
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Proliferation Assays.
Spleens were harvested and prepared as single-cell suspensions with a metal screen. RBCs were lysed by a room temperature incubation in a hypotonic solution (0.83% NH4Cl, 0.02 mM Tris, pH 7.6). Proliferation assays were set up as described previously 22. Cells assayed for proliferation were pulsed with 1 µCi/well [3H]thymidine (Amersham Pharmacia Biotech) at 48 h and harvested 18 h later.
Cytokine ELISAs.
Culture supernatant concentrations of IL-4, IL-6, IFN-
, and TNF-
were determined by sandwich ELISA with antibodies purchased from PharMingen. IL-4, IL-6, IFN-
, and TNF-
concentrations were determined from culture supernatants after 66 h of activation with soluble MOG peptide. Antibody dilutions that maximized signal to noise were determined for each antibody pair, and ELISAs were performed as described previously 22.
Serum MOG-specific Antibody Titer Determination. Serum was collected from mice by terminal cardiac puncture. Samples of serum were analyzed at various dilutions. Briefly, 96-well MAXISORPTM microtiter plates (Nunc-Nalgene) were treated with 0.2% glutaraldehyde (Sigma-Aldrich) for 2 h at 37°C. Plates were coated with pMOG35–55 (1 µg/ml in 0.1 M carbonate buffer, pH 9.6) for 3 h at 37°C and washed three times with TBS–0.1% Tween-20 (TBST). Plates were blocked overnight at 4°C with PBS containing 2% BSA (Sigma-Aldrich) and 0.05% Tween-20 and washed once with TBST. Plates were incubated with serum samples for 1 h at 37°C and washed three times with TBST. Plates were developed with anti-IgG (Calbiochem), anti-IgG1 (Caltag Laboratories), or anti-IgG2a (PharMingen) alkaline phosphatase conjugates at 37°C for 1 h and washed five times with TBST. Color was developed by incubating plates with p-nitrophenylphosphate disodium purchased from Sigma-Aldrich (1 mg/ml in 1 M carbonate buffer, pH 9.6) at room temperature for equal amounts of time. Color development was evaluated in a microplate reader at 605 nm.
Competitive Reverse Transcription PCR.
Total RNA was prepared from draining lymph node, spleen, liver, and kidney with the RNeasy MiniTM kit (QIAGEN) and stored at –70°C with 40 U of RNase-OUTTM inhibitor purchased from GIBCO BRL. cDNA was prepared from 2 µg of each sample using a kit from GIBCO BRL (Superscript II preampTM) according to the manufacturer's instructions. The cDNA was used in a PCR reaction with serial dilutions of a known molar amount of a competitive template for NOS2 (CLONTECH Laboratories, Inc.) and β-actin and performed as described previously 22.
Statistics.
Differences were statistically analyzed using unpaired Student's t test. Analysis was accomplished with STATVIEWTM (v4.5; Abacus Concepts).
| Results and Discussion |
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CFA-induced NOS2 Expression Is Partially Dependent on the Production of IFN-
and the Expression of TNFR1.
The NOS2 gene is transcriptionally activated by proinflammatory cytokines 23. We investigated whether IFN-
and TNF-
were required for CFA induction of NOS2 by immunizing C57BL/6, C57BL/6IFN-
–/–, and C57BL/6TNFR1–/– mice with CFA and evaluating them 28 d later for NOS2 mRNA expression in lymph node and spleen. We used TNFR1–/– mice rather than TNF-
–/– mice because TNFR1 is the primary mediator of TNF-
–dependent nuclear factor (NF)-
B activation, and TNF-
–/– mice have abnormal lymphoid organization 2425. As shown in Fig. 2, the NOS2 mRNA levels in lymph nodes of CFA-treated animals are significantly lower in both targeted mutant strains. Serum NOx concentrations are significantly lower as well. IFN-
–deficient mice make only a partial response, while those mice lacking TNFR1 have undetectable levels of NOS2 mRNA in the lymph node and spleen. Similar to observations made in wild-type mice, CFA-induced NOS2 mRNA expression in IFN-
–deficient mice was greater in the lymph node than in the spleen. While the difference between CFA-induced splenic NOS2 mRNA expression in wild-type and mutant mice failed to reach statistical significance, the pattern of hypoexpression is preserved (Fig. 2 B). The serum NOx levels in the CFA-immunized TNFR1–/– mice are elevated compared with unimmunized controls, although not to the extent seen in the wild type. Thus, both IFN-
and TNFR1 are required for full induction of NOS2 in response to CFA.
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2.5 in the C57BL/6 wild-type mice. NOS2–/– mice preimmunized with CFA all develop significant clinical disease by day 27. Between days 17 and 21 after MOG/CFA immunization, the disease course appears to transiently stabilize in the CFA-preimmunized animals before accelerating to fulminant disease. Therefore, while CFA preimmunization may transiently alter the course of disease in the NOS2–/– mice, it does not impart the same level of protection seen in the C57BL/6 wild-type mice.
NO-dependent CFA Immunomodulation Alters the Humoral Response after Immunization with MOG.
In a second series of experiments, we examined whether preimmunization with CFA altered the subsequent immune response to MOG/CFA in both wild-type and NOS2–/– mice. Both strains were preimmunized with CFA and then 28 d later immunized with MOG/CFA as for disease induction. On day 10 after MOG/CFA immunization, the mice were killed. Sera from experimental groups were evaluated for anti-MOG total IgG, IgG1, and IgG2a antibody titers. Spleens from all animals were assayed for their proliferative responses and cytokine production in response to MOG.
As shown in Fig. 4 A, wild-type mice pretreated with CFA have significantly augmented levels of anti-MOG IgG compared with wild-type mice not preimmunized with CFA. Under the conditions of this assay, we do not detect anti-MOG IgG in the serum of naive mice (data not shown). The total anti-MOG IgG levels in NOS2–/– mice are not augmented with CFA pretreatment and are comparable to the wild-type mice immunized with MOG/CFA. The increase in total anti-MOG IgG in CFA-pretreated wild-type mice is mainly due to a substantial increase in anti-MOG IgG1 concentrations. Again, this does not occur in NOS2–/– mice (Fig. 4 B). The increases in MOG-specific IgG2a in both strains pretreated with CFA are small but statistically significant.
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, or IFN-
. However, IL-6 production was reduced by pretreatment with CFA in an NO-dependent manner (Fig. 4 D).
CFA Pretreatment Causes an NO-dependent Reduction in Early Histologic Evidence of Inflammatory Central Nervous System Infiltrate after Immunization with MOG.
CFA-pretreated and nonpretreated mice were evaluated on day 10 after pMOG35–55 immunization for early histologic changes in the central nervous system (CNS). As shown in Fig. 5 A, wild-type mice pretreated with CFA lack the extensive infiltrate seen in CNS tissue from mice with active EAE. While CFA-pretreated wild-type mice have only minimal evidence of infiltrate, healthy NOS2–/– mice pretreated with CFA clearly show histologic changes associated with the development of EAE (Fig. 5 B). Scoring of the histology from the various groups additionally demonstrates CFA-mediated protection from early histologic disease in wild-type mice that is not observed in the absence of NOS2 (Fig. 5 C).
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B activation, which has been previously attributed to NO-dependent stabilization of I
B
32. We cannot rule out effects of NOS2-generated NO on adhesion molecule expression and egress of effector T cells from the vasculature into the CNS 33. Our results are consistent with previous studies in models of autoimmune diabetes that demonstrate important protective effects of TNF-
16. These studies provide further support for the importance of NOS2 in immunoregulation and suggest that chronic stimulation of NOS2 in vivo may have profound effects on subsequent immune responses. Given the continued interest in bacillus Calmette-Guerin vaccines for individuals predisposed to autoimmune diseases such as type I diabetes mellitus, delineation of the mechanism of the CFA effect remains an important goal.
| Acknowledgments |
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