David, Chella S.

Abstract The genetic factors that contribute to the etiology of type 1 diabetes are still largely uncharacterized. However, the genes of the MHC (HLA in humans) have been consistently associated with susceptibility to disease. We have used several transgenic mice generated in our laboratory, bearing susceptible or resistant HLA alleles, in the absence of endogenous MHC class II (Aβo), to study immune responses to the autoantigen glutamic acid decarboxylase (GAD) 65 and its relevance in determining the association between autoreactivity and disease pathogenesis. Mice bearing diabetes-susceptible haplotypes, HLA DR3 (DRB1*0301) or DQ8 (DQB1*0302), singly or in combination showed spontaneous T cell reactivity to rat GAD 65, which is highly homologous to the self Ag, mouse GAD 65. The presence of diabetes-resistant or neutral alleles, such as HLA DQ6 (DQB1*0602) and DR2 (DRB1*1502) prevented the generation of any self-reactive responses to rat GAD. In addition, unmanipulated Aβo/DR3, Aβo/DQ8, and Aβo/DR3/DQ8 mice recognized specific peptides, mainly from the N-terminal region of the GAD 65 molecule. Most of these regions are conserved between human, mouse, and rat GAD 65. Further analysis revealed that the reactivity was mediated primarily by CD4+ T cells. Stimulation of these T cells by rat GAD 65 resulted in the generation of a mixed Th1/Th2 cytokine profile in the Aβo/DR3/DQ8, Aβo/DR3, and Aβo/DQ8 mice. Thus, the presence of diabetes-associated genes determines whether immune tolerance is maintained to islet autoantigens, but autoreactivity in itself is not sufficient to induce diabetes.

Abstract Celiac disease, triggered by wheat gliadin and related prolamins from barley and rye, is characterized by a strong association with HLA-DQ2 and HLA-DQ8 genes. Gliadin is a mixture of many proteins that makes difficult the identification of major immunodominant epitopes. To address this issue, we expressed in Escherichia coli a recombinant α-gliadin (r-α-gliadin) showing the most conserved sequence among the fraction of α-gliadins. HLA-DQ8 mice, on a gluten-free diet, were intragastrically immunized with a chymotryptic digest of r-α-gliadin along with cholera toxin as adjuvant. Spleen and mesenteric lymph node T cell responses were analyzed for in vitro proliferative assay using a panel of synthetic peptides encompassing the entire sequence of r-α-gliadin. Two immunodominant epitopes corresponding to peptide p13 (aa 120–139) and p23 (aa 220–239) were identified. The response was restricted to DQ and mediated by CD4+ T cells. In vitro tissue transglutaminase deamidation of both peptides did not increase the response; furthermore, tissue transglutaminase catalyzed extensive deamidation in vitro along the entire r-α-gliadin molecule, but failed to elicit new immunogenic determinants. Surprisingly, the analysis of the cytokine profile showed that both deamidated and native peptides induced preferentially IFN-γ secretion, despite the use of cholera toxin, a mucosal adjuvant that normally induces a Th2 response to bystander Ags. Taken together, these data suggest that, in this model of gluten hypersensitivity, deamidation is not a prerequisite for the initiation of gluten responses.

Abstract Invariant chain (Ii) is a non-MHC-encoded molecule, which plays an accessory role in the proper assembly/expression of functional MHC class II molecules and there by plays an important role in Ag processing/presentation. The phenotype of mice lacking Ii depends on the allotype of the MHC class II molecule. In some mice strains, Ii deficiency results in reduction in expression of class II molecules accompanied by defective CD4+ T cell development. Responses to conventional Ags/superantigens are also compromised. In this study, we describe for the first time the functionality of human class II molecules, HLA-DQ6 and HLA-DQ8, in transgenic mice lacking Ii. HLA transgenic Ii−/− mice expressed very low levels of surface DQ6 and DQ8 accompanied by severe reduction in CD4+ T cells both in the thymus and periphery. In vitro proliferation and cytokine production to an exogenous superantigen, staphylococcal enterotoxin B (SEB) was diminished in HLA-transgenic Ii−/− mice. However, SEB-induced in vivo expansion of CD8+ T cells expressing TCR Vβ8 family in DQ8.Ii−/− mice was comparable with that of DQ8.Ii+/+ mice. Systemic IFN-γ production following in vivo challenge with SEB was reduced in DQ8.Ii−/− mice and were also protected from SEB-induced toxic shock. Although the T cell response to a known peptide Ag was diminished in DQ8.Ii−/− mice, DQ8.Ii−/− APCs were capable of presenting that peptide to primed T cells from wild-type DQ8 mice as well as to a specific T cell hybridoma. Differentiation of mature B cells was also affected to a certain extent in DQ8.Ii−/− mice.

Abstract CD28 is required to achieve optimal T cell activation to an Ag. To determine the role CD28 costimulation plays in collagen-induced arthritis, we have generated DQ8 transgenic, CD28-deficient mice. DQ8 mice deficient for CD28 had comparable numbers of CD4 and CD8 T cells as DQ8.CD28+/+ mice. DQ8.CD28−/− mice develop collagen-induced arthritis with delayed onset and less severity than DQ8.CD28+/+ mice. T cells from DQ8.CD28−/− mice did not respond to type II collagen efficiently in vitro, although the response to DQ8-restricted peptides was similar to that in the parent mice. There was no functional defect in T cells as observed by proliferation with Con A. Cytokine analysis from in vitro study showed the production of high levels of the inflammatory cytokine, IFN-γ, in response to type II collagen. We observed an increase in CD4+CD28−NKG2D+ cells after immunization, suggesting an important role for cells bearing this receptor in the disease process. CD28−/− mice also have an increased number of DX5+ cells compared with CD28+/+ mice, which can lead to the production of high levels of IFN-γ. DQ8.CD28−/− mice had an increased number of cells bearing other costimulatory markers. Cells from DQ8.CD28−/− mice exhibited a lower proliferation rate and were resistant to activation-induced cell death compared with DQ8.CD28+/+ mice. This study supports the idea that CD28 plays a crucial role in the regulation of arthritis. However, in the absence of CD28 signaling, other costimulatory molecules can lead to the development of disease, thus indicating that the requirement for CD28 may not be absolute in the development of arthritis.

Abstract We have investigated the genetic basis of the immune response to dietary gluten in HCD4/DQ8 and HCD4/DQ6 double transgenic mice. Mice were immunized with gluten i.p. or individual peptides s.c. and spleen or draining lymph node T cells were challenged in vitro. Strong proliferative responses to gluten were seen in the HCD4/DQ8 mice, whereas the HCD4/DQ6 mice responded to gluten poorly. A series of overlapping peptides spanning gliadin were synthesized. The HCD4/DQ8 mice reacted to many of the individual peptides of gliadin, while the HCD4/DQ6 mice were relatively unresponsive. T cells isolated from HCD4/DQ8 mice also responded well to modified (deamidated) versions of the gliadin peptides, whereas HCD4DQ6 mice did not. The T cell response to gluten was CD4 dependent and DQ restricted and led to the production of cytokines IL-6, TGF-β, and IL-10. Finally, intestinal lymphocytes isolated from gluten-fed HCD4/DQ8 mice displayed an activated phenotype. These data suggest that this HLA class II transgenic murine model of gluten sensitivity may provide insight into the initiation of the MHC class II-restricted gluten sensitivity in celiac disease.

Abstract We recently described a novel H2E class II-transgenic model (A−E+) of experimental autoimmune thyroiditis (EAT) that permits disease induction with heterologous thyroglobulin (Tg), but unlike conventional susceptible strains, precludes self-reactivity to autologous mouse Tg. In transgenic E+B10 (A+E+) mice, the presence of endogenous H2A genes is protective against H2E-mediated thyroiditis, inhibiting EAT development. The suppressive effect of H2A genes on H2E-mediated thyroiditis mirrors previous reports of H2E suppression on H2A-mediated autoimmune diseases, including EAT. The mechanism of the reciprocal-suppressive effect between class II genes is unclear, although the involvement of regulatory T cells has been proposed. We have recently reported that CD4+CD25+ regulatory T cells mediate peripheral tolerance induced with mouse Tg in CBA mice. To determine whether these cells play a role in our E+-transgenic model, we first confirmed the existence of CD4+CD25+ T cells regulating thyroiditis in E+B10.Ab0 (A−E+) and B10 (A+E−) mice by i.v. administration of CD25 mAb before EAT induction. The depletion of CD4+CD25+ T cells enhanced thyroiditis induction in the context of either H2E or H2A. Moreover, reconstitution of CD4+CD25+ T cells from naive B10 mice restored resistance to EAT. E+B10 (A+E+) mice were also depleted of CD4+CD25+ T cells before the challenge to determine their role in thyroiditis in the presence of both H2A and H2E genes. Depletion of CD4+CD25+ regulatory T cells offset the suppression of H2E-mediated thyroiditis by H2A. Thus, these regulatory T cells may be involved in the reciprocal-suppressive effect between class II genes.

Abstract Airway eosinophilic inflammation is a characteristic feature of allergic asthma. Exposure to allergens produced by the German cockroach (Blattella germanica) is a risk factor for allergic disease in genetically predisposed individuals, and has been linked to an increase in asthma morbidity among cockroach-sensitive inner city children. To determine the role and contribution of specific HLA class II in the pathogenesis of allergic airway inflammation in cockroach-induced asthma, we generated double-transgenic, double-knockout mice expressing human HLA-DQ8, HLA-DQ6, and CD4 molecules in the absence of mouse class II and mouse CD4. Mice were actively immunized and later challenged intranasally with cockroach allergen extract. These mice developed bronchoalveolar lavage fluid (BALF) eosinophilia and pulmonary eosinophilia. This was accompanied by an increase in total protein levels, IL-5, and IL-13 in BALF. There were also elevated levels of cockroach-specific serum IgG1 and total serum IgE. Histological analysis revealed peribronchial and perivascular eosinophilic inflammation in cockroach-treated mice. Other pathologic changes in the airways were epithelial cell hypertrophy and mucus production. Treatment with anti-DQ mAb significantly reduced pulmonary and BALF eosinophilia in cockroach allergen-sensitized mice. Aβ0 mice and transgenic mice expressing human CD4 molecule alone (without class II) or human HLA-DQ8 molecule (without CD4) treated in the same fashion showed no eosinophilia in bronchoalveolar fluid and no pulmonary parenchymal inflammation. Our results provide direct evidence that HLA-DQ molecules and CD4 T cells mediate cockroach-induced eosinophilic inflammation in the airways.

Abstract To investigate the role of HLA-DQ molecules and/or CD4+ T cells in the pathogenesis of allergic asthma, we generated HLA-DQ6 and HLA-DQ8 transgenic mice lacking endogenous class II (Aβnull) and CD4 genes and challenged them intranasally with short ragweed allergenic extract (SRW). We found that DQ6/CD4null mice developed a strong eosinophilic infiltration into the bronchoalveolar lavage and lung tissue, while DQ8/CD4null mice were normal. However, neither cytokines nor eosinophil peroxidase in the bronchoalveolar lavage of DQ6/CD4null mice was found. In addition, the airway reactivity to methacholine was elevated moderately in DQ6/CD4null mice compared with the high response in DQ/CD4+ counterparts and was only partially augmented by CD4+ T cell transfer. The DQ6/CD4null mice showed Th1/Th2-type cytokines and SRW-specific Abs in the immune sera in contrast to a direct Th2 response observed in DQ6/CD4+ mice. The proliferative response of spleen mononuclear cells and peribronchial lymph node cells demonstrated that the response to SRW in DQ6/CD4null mice was mediated by HLA-DQ-restricted CD4−CD8−NK1.1− T cells. FACS analysis of PBMC and spleen mononuclear cells demonstrated an expansion of double-negative (DN) CD4−CD8−TCRαβ+ T cells in SRW-treated DQ6/CD4null mice. These cells produced IL-4, IL-5, IL-13, and IFN-γ when stimulated with immobilized anti-CD3. IL-5 ELISPOT assay revealed that DN T cells were the cellular origin of IL-5 in allergen-challenged DQ6/CD4null mice. Our study shows a role for HLA-DQ-restricted CD4+ and DN T cells in the allergic response.

Abstract The human MHC class II genes are associated with genetic susceptibility to multiple sclerosis (MS), a chronic inflammatory demyelinating disease of the CNS of presumed autoimmune origin. These genes encode for proteins responsible for shaping immune response. The exact role of HLA-DQ and -DR genes in disease pathogenesis is not well-understood due to the high polymorphism, linkage disequilibrium, and heterogeneity of human populations. The advent of HLA class II-transgenic (Tg) mice has helped in answering some of these questions. Previously, using single-Tg mice (expressing the HLA-DR or -DQ gene), we showed that proteolipid protein (PLP)91–110 peptide induced classical experimental autoimmune encephalomyelitis only in DR3.Aβ° mice, suggesting that DR3 (DRB1*0301) is a disease susceptible gene in the context of PLP. Human population studies have suggested that HLA-DQ6 (DQB1*0601) may be a protective gene in MS. To test this disease protection in an experimental model, we generated double-Tg mice expressing both HLA-DR3 and -DQ6. Introduction of DQ6 onto DR3-Tg mice led to a decrease in disease incidence on immunization with PLP91–110 peptide indicating a dominant protective role of DQ6. This protective effect is due to high levels of IFN-γ produced by DQ6-restricted T cells, which suppressed proliferation of encephalitogenic DR3-restricted T cells by inducing apoptosis. Our study indicates that DQ6 modifies the PLP91–110-specific T cell response in DR3 through anti-inflammatory effects of IFN-γ, which is protective for experimental autoimmune encephalomyelitis. Thus, our double-Tg mouse provides a novel model in which to study epistatic interactions between HLA class II molecules in MS.

Abstract In humans, HLA-DR alleles sharing amino acids at the third hypervariable region with DRB1*0401(shared epitope) are associated with a predisposition to rheumatoid arthritis, whereas DRB1*0402 is not associated with such a predisposition. Both DRB1*0402 and DRB1*0401 occur in linkage with DQ8 (DQB1*0302). We have previously shown that transgenic (Tg) mice expressing HLA-DRB1*0401 develop collagen-induced arthritis. To delineate the role of “shared epitope” and gene complementation between DR and DQ in arthritis, we generated DRB1*0402, DRB1*0401.DQ8, and DRB1*0402.DQ8 Tg mice lacking endogenous class II molecules, AE°. DRB1*0402 mice are resistant to develop arthritis. In double-Tg mice, the DRB1*0401 gene contributes to the development of collagen-induced arthritis, whereas DRB1*0402 prevents the disease. Humoral response to type II collagen is not defective in resistant mice, although cellular response to type II collagen is lower in *0402 mice compared with *0401 mice. *0402 mice have lower numbers of T cells in thymus compared with *0401 mice, suggesting that the protective effect could be due to deletion of autoreactive T cells. Additionally, DRB1*0402 mice have a higher number of regulatory T cells and show increased activation-induced cell death, which might contribute toward protection. In DRB1*0401.DQ8 mice, activated CD4+ T cells express class II genes and can present DR4- and DQ8-restricted peptides in vitro, suggesting a role of class II+ CD4 T cells locally in the joints. The data suggest that polymorphism in DRB1 genes determines predisposition to develop arthritis by shaping the T cell repertoire in thymus and activating autoreactive or regulatory T cells.