SUITIH1 al'yAnalysis of HLA class II transgenic mice has progressed in recent years from analysis of single chain HLA class II transgenes with expression of mixed mouse/human heterodimers to double transgenic mice expressing normal human heterodimers. Previous studies have used either HLA transgenic mice in which there is a species-matched interaction with CD4 or mice which lack this interaction. Since both systems are reported to generate HLA-restricted responses, the matter of the requirement for species-matched CD4 remains unclear. We have generated triple transgenic mice expressing three human transgenes, DRA, DRB, and CD4, and compared HLA-restricted responses to peptide between human-CD4 + (Hu-CD4 +) and Hu-CD4-littermates. We saw no difference between Hu-CD4 + and Hu-CD4-groups, supporting the notion that for some responses at least the requirement for species-matched CD4 may not be absolute. Evidence for positive selection of mouse T cell receptors in HLA-DR transgenic mice came both from the acquisition of new, HLA-restricted responses to various peptides and from an increased frequency of T cells using the TCR V34 gene segment. An important goal with respect to the analysis of function in HLA transgenic mice is the clarification of mechanisms which underpin the recognition of self-antigens in human autoimmune disease. As a first step towards 'humanized' disease models in HLA transgenic mice, we analyzed the responses of HLA-DR transgenic mice to the human MPB 139-154 peptide which has been implicated as an epitope recognized by T cells of multiple sclerosis patients. We obtained T cell responses to this epitope in transgenic mice but not in nontransgenic controls. This study suggests that HLA transgenic mice will be valuable in the analysis of HLA-restricted T cell epitopes implicated in human disease and possibly in the design of new disease models.

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Glutamic acid decarboxylase (GAD65) has been implicated as a targeted self antigen in the immune destruction of pancreatic beta cells. T cell responses to GAD65 peptides have been detected in both patients with type I diabetes and in the non-obese diabetic (NOD) mouse. To establish which GAD65 epitopes are important in the immunopathogenesis of disease we initially compared T cell responses to GAD65 epitopes in conditions of disease susceptibility and protection. T cell responses to GAD65 peptides were measured in monozygotic twin pairs selected on the basis of disease discordance and T cell recognition of immunogenic regions of GAD65. Peptides of interest were then used to immunize susceptible NOD mice and H2-E transgenic NOD mice which are protected from diabetes. A differential response to the epitope GAD65 521-535 discriminated diabetic from non-diabetic human twins as well as susceptible from protected mice. This epitope as well as GAD 505-519 induces T cell responses despite binding the type I diabetes associated HLA-DQA1*0301/DQB1*0302 product with low affinity. Since DQ-restricted T cell responses are difficult to study in humans, HLA-DQ8 transgenic mice were then used: GAD epitopes 521-535 and 505-519 induced responses in DQ8 transgenic mice and T cell lines were established. Long-term T cell lines against GAD 505-519 were HLA-DQ restricted, and responded to peptide with a strong IFN-gamma and IL-10 response. The findings implicate GAD 521-535 as a possible target peptide in pathogenesis and are compatible with a model whereby self-reactive T cells specific for low-affinity peptide-MHC complexes may escape thymic negative selection.

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