DEVELOPMENT OF AN I-A(G7)-EXPRESSING ANTIGEN-PRESENTING CELL-LINE - INTRINSIC MOLECULAR DEFECT IN COMPACT I-A(G7) DIMER GENERATION

Insulin-dependent diabetes mellitus (IDDM) results from chronic, T-cel l dependent, autoimmune destruction of the insulin-producing beta-cell s in the Langerhans' islets of the pancreas. Non-obese diabetic (NOD) mice spontaneously develop IDDM that resembles human type I diabetes. The susceptibility to diabetes in the NOD strain is a complex polygeni c trait that determines a phenotype of immune alterations. The unique MHC class II molecule expressed by NOD mice (I-A(g7)) plays a major ro le in the development of disease. Recently, it has been reported that I-A(g7) molecules generate a lower proportion of compact alpha beta he terodimers, compared to other haplotypes. However, it is not clear whe ther this reflects an intrinsic defect of this molecule to bind peptid e stably or is the result of abnormal processing and/or peptide loadin g into the I-A(g7) molecule. Our aim was to develop and characterize a suitable antigen-presenting cell (APC) that expressed I-A(g7) in the context of a non-diabetes-prone antigen processing and presentation ma chinery. Here, we report the generation of a mouse DAP.3 fibroblast ce ll line (DAP.3A(g7)) that constitutively expresses high levels of I-A( g7). Using DAP.3 cells transfected a with I-A(g7) or I-A(k), we show t hat the expression of compact dimers in the same cell type is proporti onally less for I-A(g7) molecules than for I-Ak molecules, implying an intrinsic defect of the I-A(g7) molecule as the cause for the low gen eration of compact dimers. However, DAP.3A(g7) cells are able to proce ss and present antigen, as indicated by I-A(g7)-dependent IL-2 product ion by a GAD67-specific NDO T-cell hybridoma after stimulation with GA D and live, but not fixed, DAP.3A(g7) cells. The IL-2 response to GAD when presented by DAP.3A(g7) was significantly higher than the respons e to GAD presented by NOD splenocytes. Based on these data, we conclud e that the low generations of compact dimers is an intrinsic feature o f I-A(g7) molecules and not affected by other genes in the NOD backgro und. The DAP.3A(g7) cell line should be a valuable tool with which to dissect the role of the I-A(g7) molecule in antigen presentation and T -cell activation in NOD mice, which clearly contributes to the develop ment of IDDM. (C) 1998 Academic Press Limited.