Transgenic mice with I-A on islet cells are normoglycemic but immunologically intolerant

T cell-dependent class II major histocompatibility complex antigen expression in vivo induced by the diabetogen streptozotocin

Immune reactions are involved in the low-dose streptozotocin (STZ)-model of hyperglycemia (1). By means of the popliteal lymph node assay, we demonstrated that T cell-dependent lymphoproliferation can be evoked by STZ (2). The present report shows that class II MHC antigen expression is readily inducible in multiple organs by a single dose of STZ injected subcutaneously (s.c.) into BALB/cJ mice. An increment of class II-positive cells of the lymphocyte and monocyte/macrophage lineage is discernible in the endocrine pancreas, kidney, and liver, but not the brain. In addition, renal tubular and bile duct epithelium express strong class II positivity. Class II antigens are not visible on pancreatic endocrine cells and hepatocytes. These immune phenomena are T cell-dependent, as assessed in tissues from BALB/cJ nu/nu recipients and their +/nu counterparts. STZ-induced class II antigens develop transiently and are not necessarily associated with organ dysfunction. The present STZ-induced MHC class II antigen aberrancies are in agreement with observations described recently by COCKFIELD et al. (3). In addition, we found that injection of methylnitrosourea, the aglycone of STZ, also resulted in class II MHC molecule induction in the liver, whereas the diabetogen alloxan failed to exert any effect on class II antigens.

Peripheral self-tolerance and autoimmunity: the protective role of expression of class II major histocompatibility antigens on non-lymphoid cells

Immunologic self-tolerance is achieved mainly during development by clonal deletion in the thymus of T lymphocytes with receptors specific for self-antigens and with associated T-cell markers CD4/CD8. However, T cells expressing a low level of these markers are allowed into the periphery still bearing their autospecific receptors. Such clonal deletion, induced by cells bearing the class II antigens coded for by major histocompatibility complex (MHC) in the thymus, does not remove all autoreactive T cells specific for antigens of differentiated tissue expressed extrathymically. However, these autoreactive T cells are silent in the periphery. Peripheral non-lymphoid cells (e.g., endocrine cells) can induce antigen-specific unresponsiveness in T cells and can specifically suppress production of autoantibody against their antigens when the non-lymphoid cells express class II MHC antigens on their surface. This class II MHC expression is induced by interferon-gamma produced by T cells as a result of various immune responses, such as autoimmune reaction. Thus, the expression of class II MHC antigens on non-lymphoid cells may serve as a peripheral mechanism for the induction and maintenance of self-tolerance in autoreactive T cells that escape negative selection in the thymus or that are specific for extrathymic tissue antigens, in a fail-safe mechanism against autoimmunity. Some autoimmune diseases, especially organ-specific ones, might be caused by a defect in this fail-safe mechanism.