Understanding how T lymphocytes recognize beta-cell autoantigens is essential for the elucidation of the pathogenesis of insulin-dependent diabetes mellitus. The increased and ectopic expression of HLA class I and II molecules detected in human beta-cells may facilitate this interaction. T-lymphocyte recognition of surface antigens also involves adhesion accessory molecules: intercellular adhesion molecule 1 (ICAM-1) and lymphocyte function-associated antigen 3 (LFA-3). These molecules not only allow cell contact but can also provide costimulatory signals for T-lymphocyte activation. Levels of ICAM-1 and LFA-3 expression in normal human islet cells and regulation of their expression by cytokines interferon-gamma (IFN-gamma), tumor necrosis factor alpha (TNF-alpha), interleukin 1 beta (IL-1 beta), and IL-6 have been studied by two-color immunofluorescence staining of pancreatic cryostat sections and fluorescence-activated cell sorter analysis. Neither ICAM-1 nor LFA-3 could be demonstrated in sections or in fresh cell preparations, but after 18 h of culture, beta-, alpha-, and delta-cells expressed spontaneously moderate levels of ICAM-1 (but not LFA-3). IFN-gamma and TNF-alpha alone or in combination strongly enhanced this spontaneous expression of ICAM-1 in a time- and/or dose-dependent and additive manner but had no effect on LFA-3. An SV40-transformed islet cell line showed high basal levels of both ICAM-1 and LFA-3, but the response to cytokines followed the same pattern as primary cultures.(ABSTRACT TRUNCATED AT 250 WORDS)
Since their demonstration in 1975, ICSAs have been proposed as serological markers and pathogenic elements in IDDM. ICSAs are detected in the sera of most newly diagnosed IDDM patients by indirect IFL that uses viable preparations of rat islet or insulinoma cells as substrate, but they also can be detected by using human insulinoma or fetal islet cells. We have tried to demonstrate ICSAs in the sera of 31 newly diagnosed diabetic patients, including 6 positive samples on human fetal islet cells, which used their natural target for the first time: normal human islet cells. In spite of using different types of preparations of these cells (i.e., freshly dispersed cell suspensions, monolayer cultures, or dispersed islets after culture), ICSAs could not be detected by IFL under the UV microscope, nor by flow cytometry. In contrast, 9 of 29 of the sera gave a positive staining on the RIN rat insulinoma cells. In an attempt to establish whether the putative ICSA autoantigen is present in the surface of human islet cells in the diabetic pancreas, the insulitis microenvironment was emulated by exposing the islets to three types of stress: 1) cytokines (IFN-gamma and TNF-alpha); 2) heat shock; and 3) hyperglycemia. However, diabetic sera failed again to recognize membrane antigens on the islet cells after either of these treatments. Neither were islet cells from a newly diagnosed diabetic patient stained by its autologous serum (ICA titer > 80 JDF U). These results suggest that ICSA autoantigen is not expressed in the membrane of human islet cells and therefore raises doubts about their proposed pathogenic role.
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