TUMOR-NECROSIS-FACTOR-ALPHA MODIFIES ADHESION PROPERTIES OF RAT ISLETB-CELLS

The characteristic three-dimensional cell type organization of islets of Langerhans is perturbed in animal models of diabetes, suggesting th at it may be important for islet function. Rat islet cells in culture are able to form aggregates with an architecture similar to native isl ets (pseudoislets), thus providing a good model to study the molecular basis of islet architecture and its role in islet function. Sorted is let B cells and non-B cells were permanently labeled with two differen t fluorescent dyes (DiO and DiI), mixed, and allowed to form aggregate s during a 5-d culture in the presence or absence of TNF-alpha (100 U/ ml), a cytokine suggested to be implicated in the early physiological events leading to insulin-dependent diabetes mellitus. Confocal micros copy of aggregates revealed that TNF-alpha reversibly perturbs the typ ical segregation between B and non-B cells. Insulin secretion, was alt ered in the disorganized aggregates, and returned towards normal when pseudoislets had regained their typical architecture. The homotypic ad hesion properties of sorted B and non-B cells cultured for 20 h in the presence or absence of TNF-alpha were studied in a short term aggrega tion assay. TNF-alpha induced a significant rise in Ca2+-independent a dhesion of B cells (from 24+/-1.1% to 44.3+/-1.2%; n = 4, P < 0.001 ). These findings raise the possibility that the increased expression of Ca2+-independent adhesion molecules on B cells leads to altered islet architecture, which might be a factor in the perturbation of islet fu nction induced by TNF-alpha.