HLA-B27 transgenic mice are susceptible to collagen-induced arthritis: type II collagen as a potential target in human disease

HLA-B27 is highly linked with a group of human diseases called spondyloarthropathies (SpA). Many of these disorders begin after an infection with an enterobacteria. The symptoms seen in patients with spondyloarthropathies are inflammatory pain in the spine and asymmetrical arthritis of lower limbs. Additional symptoms related to SpA include inflammation in the eyes, bowel, and skin. The autoantigen(s) in SpA are not known. Proteins such as collagen and proteoglycans have been thought to be potent autoantigens in arthritidis including B27-associated human diseases. Type II collagen is a common denominator among eyes and joints, affected tissues in B27-linked diseases. Moreover, a few reports indicated CII specific T cells and antibodies in patients with spondyloarthropathies. We and others have previously described development of spontaneous arthritis and nail disease in HLA-B27 transgenic animals. To determine whether CII may be a target antigen in the B27-linked diseases, B27 + m beta 2 m% (HLA-B27) transgenic mice lacking mouse beta 2m with and without human beta 2m) mice were immunized with type II collagen inside the barrier facility. Male HLA-B27 transgenic mice developed collagen-induced arthritis compared to transgene negative littermates or female counterparts. There was no difference in the incidence of arthritis in HLA-B27 transgenic mice with and without human beta 2m. Our data suggest that beta 2m free heavy chain of HLA-B27 may present soluble antigens such as type II collagen to trigger specific T cells contributing in the development of arthritis. Our data also suggest that CII may be a potential target antigen in the cartilage during the disease process.     

Peptide binding alpha1alpha2 domain of HLA-B27 contributes to the disease pathogenesis in transgenic mice

Human spondyloarthropathies are strongly associated with a major histocompatibility complex (MHC) class I allele, HLA-B27. HLA-B27 transgenic mice and rats demonstrate many features of these diseases further confirming the role of HLA-B27 in disease. Yet the exact role of this molecule in disease pathogenesis is not clearly understood. We have previously reported spontaneous arthritis and nail disease in HLA-B27 transgenic mice lacking beta2-microglobulin (B27+beta2m(o)). These observations along with binding studies of B27 derived peptides to HLA-B27 molecule itself led to two hypotheses: (i) HLA-B27 derived peptide as a source of autoantigen; and (ii) HLA-B27 functions as an antigen presenting molecule. In this report, we confirm spontaneous disease in transgenic mice expressing a hybrid B27 molecule with alpha1alpha2 domain of B27 and alpha3 domain of mouse H-2Kd. These mice developed spontaneous arthritis and nail disease when transferred from specific pathogen free barrier facility to the conventional area. Other control mice with MHC class I transgene (e.g., HLA-B7, HLA-Cw3, and H2-Dd) did not develop such disease. In a MHC reassembly assay, binding of similar peptides to both wild type and hybrid B27 molecules was observed. In addition, the hybrid B27 molecule lacks at least one of the 3 proposed peptides from the third hypervariable (HV3) region of HLA-B27. These data strongly suggest that HLA-B27 molecule is an antigen presenting molecule rather than a peptide donor in the disease pathogenesis.     

HLA expression and function in single and double HLA-B27-transgenic mice

The expression and function of HLA antigens in mice single transgenic for HLA-B27.2 (sTGM-B27.2) or double transgenic (dTGM) for HLA-B27.2 and human beta 2-microglobulin (h beta 2m) were compared. B27.2 could be well detected on the cell membrane of lymphocytes of sTGM. However, the expression in sTGM was much lower than in dTGM mice. Nevertheless, also in sTGM mice, the B27-transgene product possessed all functional properties of a class I HLA molecule. This was shown by the recognition and induction of antibodies and cytotoxic T cells, by the induction of "allo"-immunity, including skin graft rejection, and by the ability to present viral antigens. In dTGM, the expression of B27 on peripheral blood lymphocytes, spleen and lymphnode cells was comparable to H-2. However, on thymocytes, a relatively lower expression of HLA than H-2 was observed. This low expression of B27 on thymocytes is in concert with the observation that B27 is expressed only in the medulla of the thymus and not detectable in the cortex.     

Characterization of psoriasiform and alopecic skin lesions in HLA-B27 transgenic rats.

We have previously reported a multisystem inflammatory disease in transgenic rat lines with high expression of HLA-B*2705 and human beta 2 microglobulin. Skin disease in these rats includes two predominant lesions: 1) marked psoriasiform dermatitis of the tail and digits; and 2) progressive alopecia of face, neck, trunk, and extremities. Here we present the results of a systematic survey of these lesions. Tail and digit skin showed psoriasiform hyperplasia of the epidermis associated with parakeratosis, with marked dermal and epidermal inflammation. The alopecic skin showed perifollicular and follicular mononuclear infiltration and increased numbers of atrophic follicles. Immunohistochemical analysis revealed that B27 expression was prominent on keratinocytes in hyperplastic epidermis where lymphocytic infiltrates were prominent, but was absent in the absence of inflammation. In alopecic lesions, B27 was strongly expressed on follicular epithelium and dermal hair papillae associated with mononuclear infiltrates. T cells, both CD8 and CD4, were most prominent in inflammatory lesions and rat MHC-II expression on keratinocytes, and follicular epithelium was dramatically increased. This study suggests that T cell-mediated immune mechanisms participate in development of cutaneous lesions in HLA-B27 transgenic rats.     

Human HLA-B27 gene enhances susceptibility of rats to oral infection by Listeria monocytogenes.

Germfree rats transgenic for the human genes HLA-B27 and beta 2-microglobulin were colonized with hemolysin-positive (Hly+) or hemolysin-negative (Hly-) strains of Listeria monocytogenes. HLA-B27 rats were very susceptible to infection with Hly+ L monocytogenes none survived beyond 6 days. Conversely, nontransgenic control rats survived alimentary tract colonization with the Hly+ strain, and both transgenic and nontransgenic rats survived colonization with the Hly- strain of L monocytogenes. After colonization with Hly+ L monocytogenes, both transgenic and nontransgenic rats developed severe bowel inflammation which consisted histologically of microab scesses, granulomatous lesions, and ulcers; however, whereas the transgenic rats died within 6 days, only very mild intestinal lesions were seen in nontransgenic rats 10 to 42 days after colonization. Liver and splenic lesions were small and transient in nontransgenic rats. Transgenic and nontransgenic control rats infected with Hly- Listeria developed mild transient diarrhea but showed no histological changes in the intestine. This study thus documents an association between a particular bacterial product (hemolysin produced by L monocytogenes) and the induction of severe inflammatory disease and death in rats expressing HLA-B27 and beta 2-microglobulin.     

Susceptibility of HLA-B27 transgenic mice to Yersinia enterocolitica infection

The majority of patients with reactive arthritis have the major histocompatibility complex class I gene HLA-B27. The development of arthritis in these patients often occurs following infection with one of several enteric bacteria, including Yersinia enterocolitica. In this study, transgenic mice expressing HLA-B27 and their negative full sibs were infected intravenously with Yersinia enterocolitica 0:8 WA in an attempt to develop an experimental model of reactive arthritis. To date, no reactive arthritis has been observed; however, a significantly higher incidence of paralysis was observed in the HLA-B27⁺ transgenic mice. Injection of 10⁵ organisms induced hind limb paralysis in 8 out of 30 of the HLA-B27 transgenic mice (27%) and in only 1 of the 24 negative siblings (4%). Paralysis occurred in 14 out of 30 HLA-B27⁺ mice (47%) at a dose of 10⁴ organisms. Only 2 of the 25 negative siblings (8%) were affected at this dose. Paraspinal abscesses were found in all of the paralyzed animals. At the 10⁴ dose most of the HLA-B27⁺ mice (70%) succumbled to the disease within 4 weeks, while the mortality in their B27⁻ full sibs was less than 10%. Thus, HLA-B27 transgenic mice have higher mortality and morbidity from infection with Y. enterocolitica 0:8 WA than corresponding HLA-B27⁻ littermates.     

Inflammatory disease in HLA-B27 transgenic rats

Summary: A spontaneous inflammatory disease in rats transgenic for HLAB27 resembles the B27-associated human spondyloarthropathies, Colitis and arthritis, the two most important features, require T cells, gut bacteria, and high expression of B27 in bone marrow-derived cells, Control rats with HLA-B7 remain healthy. Most rats with HLA-Cw6 (associated with psoriasis vulgaris) remain healthy; a minority develop mild and transient disease. Rats with a mutant B27 with a Cys67←Ser substitution resemble wild-type B27 transgenics, but with a lower prevalence of arthritis. A similar phenotype is seen in B2 7 rats co-expressing a viral peptide that binds B27. Disease-prone LEW but not F344 B27 rats develop high serum IgA levels concurrent with disease progression. Colitis is associated with high interferon-y, arthritis with high interleukin-6. Disease is similar in B27 LEW, F344, and PVG rats, but the DA background is protective. Conclusions: The spondyloarthropathy-like disease in rats is specific for HLA-B27 but does not require Cys67. Arthritis but not colitis is particularly sensitive to B27 peptide-binding specificity. Genetic background exerts a strong influence, but some phenotypic differences exist between permissive strains that do not influence disease susceptibility The data favor a role for B27 peptide presentation in arthritis, but other mechanisms to explain the role of B27 have not been excluded.     

Lymphoblastoid cells express HLA-B27 homodimers both intracellularly and at the cell surface following endosomal recycling

The MHC class I allele HLA-B27 is very strongly associated with development of autoimmune spondyloarthritis, although the disease mechanism remains unknown. Class I molecules classically associate in the endoplasmic reticulum (ER) with beta2-microglobulin (beta(2)m) and antigenic peptides for cell surface expression and presentation to T cells. We have previously shown that HLA-B27 is capable of forming beta(2)m-free disulfide-bonded homodimers in vitro. Here we show that HLA-B27 forms disulfide-bonded homodimers in vivo by two distinct pathways. HLA-B27 homodimers form in the ER but appear unable to egress to the cell surface in human cells. Cell surface HLA-B27 homodimers are abundantly expressed in a variety of lymphoid cell lines. Experiments with inhibitors indicate that HLA-B27 homodimers can arise from cell-surface heterodimers via an endosome-dependent recycling pathway. HLA-B27 homodimer expression on the cell surface of 721.220 is dependent on the unpaired cysteine(67) and is inhibited by restoration of tapasin function or by incubation with peptides that bind strongly to HLA-B27 heterodimers. Cell surface expressed HLA-B27 homodimers are likely to be immunologically reactive ligands for NK family immunoreceptors and, hence, could play a pathogenic role in spondyloarthritis.     

Ankylosing spondylitis: a beta2m-deposition disease?

To explain the strong association between HLA-B27 and ankylosing spondylitis, we suggest that the release of beta(2)-microglobulin (beta(2)m) from a subpopulation of cell surface-expressed HLA-B27 molecules leads to beta(2)m-deposition within synovia and to the initiation of an inflammatory process, which culminates in destructive spondyloarthropathy.     

Demonstration of cross-reactivity between bacterial antigens and class I human leukocyte antigens by using monoclonal antibodies to Shigella flexneri

Bacterial envelope proteins which share immunodeterminants with the human leukocyte antigen (HLA) class I histocompatibility antigen HLA-B27 may invoke spondyloarthritic disease through the process of molecular mimicry in patients expressing this phenotype. Monoclonal antibodies generated by the immunization of BALB/c mice with envelope proteins of Shigella flexneri type 2a were tested for reactivity against cultured lymphoblastoid cell lines of defined HLA phenotype. As measured by flow microfluorometry, four immunoglobulin M monoclonal antibodies reacted preferentially with HLA-B27-positive lymphocytes (HOM-2, MM) as compared with a B27-loss mutant line (1065) or cells lacking major histocompatibility complex class I antigen (Daudi, K562). Monoclonal antibodies also reacted with mouse EL-4 cells transfected with and expressing the HLA-B7 gene. Western immunoblot analysis of isolated enterobacterial envelopes demonstrated that the reactive epitope was present on bacterial proteins with an apparent relative molecular mass of 36 and 19 kilodaltons. The structural basis for the cross-reactivity of bacterial antigen and HLA-B27 appeared to reside in the portion of the HLA molecule that is responsible for allotypic specificity (amino acids 63 through 83), since monoclonal antibodies were positive by enzyme-linked immunosorbent assay with synthetic polypeptides corresponding to this segment.     

Role of commensal bacteria in chronic experimental colitis: lessons from the HLA-B27 transgenic rat.

Rats on Lewis or Fischer background, transgenic for human HLA-B27 and beta(2)-microglobulin genes spontaneously develop colitis, gastritis, arthritis, dermatitis, orchitis, epididymitis, carditis, alopecia and nail changes. Disease susceptibility correlates with the gene copy number and is influenced by the genetic background. The pathomechanism in this model is still not completely understood. Cell transfer experiments indicate an essential role of HLA-B27 expression in bone marrow-derived cells. On Fischer background the onset of colitis occurs at 2 months of age, peaks at 3 months of age, and plateaus. Histologic findings include inflammatory cell infiltration, mostly limited to the mucosa, crypt hyperplasia, reduction of goblet cells, occasionally crypt abscesses and early ulcers. There is evidence that normal luminal bacteria play an essential role in initiating and perpetuating chronic colitis and gastritis in HLA-B27 transgenic rats: Transgenic rats raised under germ-free conditions do not develop gastrointestinal disease, whereas transgenic littermates exposed to specific pathogen-free bacteria develop colitis and gastritis within 2-4 weeks. Obligate anaerobic bacteria, especially Bacteroides spp., may play a predominant role since metronidazole prevents colitis and transgenic germ-free rats contaminated with a cocktail of six obligate and facultative anaerobic bacteria develop colitis and gastritis only in the presence of Bacteroides vulgatus. Luminal bacteria may also be involved in trafficking and homing of inflammatory cells into remote organs, since varying cecal bacterial composition does not only alter local inflammation but also influences gastritis. Lymphocyte transfer experiments indicate a specific response to luminal bacteria. In summary, this animal model is suitable for investigating the influence of normal luminal bacteria on the cellular immune mechanism in chronic intestinal inflammation.     

Adoptive transfer of nontransgenic mesenteric lymph node cells induces colitis in athymic HLA-B27 transgenic nude rats

HLA-B27 transgenic (TG) rats develop spontaneous colitis when colonized with intestinal bacteria, whereas athymic nude (rnu/rnu) HLA-B27 TG rats remain disease free. The present study was designed to determine whether or not HLA-B27 expression on T cells is required for development of colitis after transfer of mesenteric lymph node (MLN) cells into rnu/rnu HLA-B27 recipients. Athymic nontransgenic (non-TG) and HLA-B27 TG recipients received MLN cells from either TG or non-TG rnu/+ heterozygous donor rats that contain T cells. HLA-B27 TG rnu/rnu recipients receiving either non-TG or TG MLN cells developed severe colitis and had higher caecal MPO and IL-1beta levels, and their MLN cells produced more IFN-gamma and less IL-10 after in vitro stimulation with caecal bacterial lysate compared to rnu/rnu non-TG recipients that remained disease free after receiving either TG or non-TG cells. Interestingly, proliferating donor TG T cells were detectable one week after adoptive transfer into rnu/rnu TG recipients but not after transfer into non-TG recipients. T cells from either non-TG or TG donors induce colitis in rnu/rnu TG but not in non-TG rats, suggesting that activation of effector T cells by other cell types that express HLA-B27 is pivotal for the pathogenesis of colitis in this model.     

Progression of HIV to AIDS: a protective role for HLA-B27?

HLA-B27 is known for its strong association with inflammatory spondyloarthropathies (SpA), a group of rheumatic diseases. Apart from playing its role in the onset of these inflammatory diseases, HLA-827 is so ubiquitous in the world that the carrying of this gene must have also have an advantage. There are some indications that a beneficial effect can be found as a less severe course of viral infections among B27-carriers. The literature on this subject was reviewed and revealed a favorable course of infection with influenza virus, herpes simplex type 2 virus, Epstein-Barr virus and, even more interesting, a protective effect of HLA-B27 in the progression of HIV infections. The course of HIV infection differs among individuals and is thought to be partly related to host-factor variability, reflecting broad genetic heterogeneity. The polymorphic human leukocyte antigens (HLA) are herein analyzed intensively with respect to this relationship. Cytotoxic T lymphocyte (CTL) responses, activated by HLA antigen presentation, are implicated in the control of HIV replication. An immunological explanation for the protective role for HLA B27 in HIV disease is that B27+ patients have a specific and strong CTL response against the p24 epitope, a conservative HIV protein that does not easily mutate. Some HLA genes seen in long-term non-progressors (LTNP) (>10 years disease free) are associated with a favorable prognosis. One of the alleles found predominantly in LTNPs is HLA-B27. More genetic factors seem to influence disease progression in HIV infections. Therefore, it would be interesting to further explore the influence of the genetic make up of these HIV-infected individuals. Knowledge of the immunogenetic profile might give clues for the individual course of the HIV infection, may influence the development of drug-resistant viruses and will possibly lead to a tailored therapeutic strategy in HIV-infected persons.     

Transgenic mice expressing human HLA and CD8 molecules generate HLA-restricted measles virus cytotoxic T lymphocytes of the same specificity as humans with natural measles virus infection

Control of primary measles virus (MV) infection in humans and continued maintenance of immune memory that protects against reinfection are mediated primarily through the anti-MV T cell response, as judged by observations of children with defects in antibody formation but competency in making T cells. Further, the failure of T cell responses in those infected with MV most often leads to overwhelming infection. To better define and manipulate the elements involved in human T cell responses to MV, we analyzed the generation of HLA-restricted cytotoxic T lymphocytes (CTL) in a small animal model. Transgenic mice expressing the human class I MHC antigen HLA-B27 in conjunction with human CD8 molecules produced vigorous HLA-restricted CTL responses to MV antigens, paralleling those in MV infection of humans. In addition, such humanized mice generated human CD8 coreceptor-dependent HLA-B27-restricted CTL with the same specificity for recognition of MV fusion (F) peptide RRYPDAVYL as reported for humans during natural MV infection. Neither murine beta(2)-microglobulin nor murine CD8 substituted adequately as coreceptors for the HLA-B27 heavy chain. By contrast, HLA-A2.1-restricted responses to measles could be generated in the absence of expression of human beta(2)-microglobulin or CD8(+) molecules in HLA-A2.1/K(b) transgenic mice. Thus a small animal model is now available for studying strategies for optimizing human CD8(+) T cell responses and for testing vaccines. This model offers the potential, when combined with the newly reported CD46 transgenic mouse model in which MV replicates in cells of the immune system, for uncoding the molecular mechanism of MV-induced immunosuppression.     

HLA-B27等位基因和亚型与强直性脊柱炎关系研究进展

大量的研究证明,强直性脊柱炎(AS)是与人类白细胞抗原(HLA)相关性最强的疾病。AS的发病与HLA-B27阳性密切相关,并与B7、B13、B40等几个等位基因有一定关系。HLA-B位点有42个等位基因,其中HLA-B27具有高度多态性,含有22个以上的亚型,不同亚型的碱基序列间只有个别差异。B27亚型在AS患者中的分布因地区和种族上的差别而不同,在中国主要以B2704和B2705为主,但以B2705分布最广。这几年大量的人B27转基因鼠实验证明AS与B27的关联性。     

From HLA-B27 to spondyloarthritis: a journey through the ER

Summary: Almost four decades of research into the role of human leukocyte antigen-B27 (HLA-B27) in susceptibility to spondyloarthritis has yet to yield a convincing answer. New results from an HLA-B27 transgenic rat model now demonstrate quite convincingly that CD8⁺ T cells are not required for the inflammatory phenotype. Discoveries that the HLA-B27 heavy chain has a tendency to misfold during the assembly of class I complexes in the endoplasmic reticulum (ER) and to form aberrant disulfide-linked dimers after transport to the cell surface have forced the generation of new ideas about its role in disease pathogenesis. In transgenic rats, HLA-B27 misfolding generates ER stress and leads to activation of the unfolded protein response, which dramatically enhances the production of interleukin-23 (IL-23) in response to pattern recognition receptor agonists. These findings have led to the discovery of striking T-helper 17 cell activation and expansion in this animal model, consistent with results emerging from humans with spondyloarthritis and the discovery of IL23R as an additional susceptibility gene for ankylosing spondylitis. Together, these results suggest a novel link between HLA-B27 and the T-helper 17 axis through the consequences of protein misfolding and open new avenues of investigation as well as identifying new targets for therapeutic intervention in this group of diseases.     

Cytotoxic T-Cell-Mediated Response against Yersinia pseudotuberculosis in HLA-B27 Transgenic Rat

Yersinia-induced reactive arthritis is highly associated with HLA-B27, the role of which in defense against the triggering bacteria remains unclear. The aim of this study was to examine the capacity of rats transgenic for HLA-B27 to mount a cytotoxic T-lymphocyte (CTL) response against Y. pseudotuberculosis and to determine the influence of the HLA-B27 transgene on this response. Rats transgenic for HLA-B*2705 and human beta(2)-microglobulin of the 21-4L line, which do not spontaneously develop disease, and nontransgenic syngeneic Lewis (LEW) rats were infected with Y. pseudotuberculosis. Lymph node cells were restimulated in vitro, and the presence of for Y. pseudotuberculosis-specific CTLs against infected targets was determined. Infection of 21-4L rats triggered a CD8(+) T cell-mediated cytotoxic response specific for Y. pseudotuberculosis. Analysis of this response demonstrated restriction by an endogenous major histocompatibility complex molecule. However, no restriction by HLA-B27 was detected. In addition, kinetics studies revealed a weaker anti-Yersinia CTL response in 21-4L rats than in nontransgenic LEW rats, and the level of cytotoxicity against 21-4L lymphoblast targets sensitized with Y. pseudotuberculosis was lower than that against nontransgenic LEW targets. We conclude that HLA-B27 transgenic rats mount a CTL response against Y. pseudotuberculosis that is not restricted by HLA-B27. Yet, HLA-B27 exerts a negative effect on the level of this response, which could contribute to impaired defense against Yersinia.     

Cerebral expression of interleukin-12 induces neurological disease via differential pathways and recruits antigen-specific T cells in virus-infected mice

Transgenic expression of interleukin-12 (IL-12) in astrocytes causes a spontaneous inflammatory central nervous system disorder in aged mice. Here we show that spontaneous disorder developed only when both mature lymphocytes and interferon (IFN)-gamma were present. Infection with noncytolytic Borna disease virus (BDV) did not affect wild-type mice but accelerated disease of IL-12 transgenic mice. Infection of transgenic mice lacking lymphocytes did not result in neurological symptoms. In contrast, BDV infection of transgenic mice lacking IFN-gamma induced neurological disease with delayed onset of symptoms that resembled those in infected transgenic mice with a functional IFN-gamma gene. In BDV-infected transgenic mice devoid of IFN-gamma no cerebellar calcification was observed, and multiplication of BDV was not inhibited. To determine the antigen specificity of lymphocytes in brains of diseased animals, the IL-12 transgene was introduced into an H-2k genetic background. Infection of IL-12 transgenic H-2k mice resulted in extensive lymphocytic infiltration into the cerebellum but not into other brain regions that also contained viral antigen but expressed the transgene at lower levels. Tetramer analysis revealed that most CD8 T cells in the cerebellum of such mice were BDV-specific. Our results thus demonstrate that IFN-gamma secreting lymphocytes are responsible for disease of IL-12 transgenic mice. They further suggest that expression of IL-12 in the central nervous system may lead to localized recruitment of T cells that recognize antigens expressed in the brain.     

Colitis in HLA-B27/beta 2 microglobulin transgenic rats

Rats of susceptible genetic backgrounds expressing high copy numbers of the transgene encoding HLA-B27 and human beta 2 mu develop chronic colitis complicated in the advanced stage by adenomatous polyps progressing to adenocarcinoma. Unique features of this model include a spectrum of extraintestinal manifestations resembling to some extent human spondyloarthropathy, with peripheral and axial joint, dermatologic and male genital inflammation. Inflammation is T lymphocyte mediated, although surprisingly CD4+ cells are more active in transferring disease than CD8+ cells, which would be expected to be preferentially activated by Class I MHC peptides. Inflammation is dependent on a nonlymphoid bone marrow-derived cell, expressing high copy numbers of B27, probably APCs. In vitro function of transgenic dendritic cells is deficient, and in vivo competition for peptide binding in the antigen binding site of B27 attenuates arthritis. Normal bacteria are required for disease expression, with B. vulgatus preferentially able to induce colitis, whereas other bacteria such as E. coli stimulate no inflammatory response. Inflammation and resulted complications are modulated by non-MHC genes and are amenable to treatment by bone marrow transplant from normal donors. These results support the hypothesis that gastrointestinal and systemic inflammation in B27 transgenic rats is the result of loss of tolerance to enteric bacteria, as a consequence of defective APC (? dendritic cells) function. Whether disease is the result of selective MHC binding of enteric antigens uniquely capable of inducing disease, lack of appropriate induction of a CD8+ suppressor cell population, or skewed cytokine (IL-12, IL-18) secretion by APCs remains to be determined.