Modulation of the effect of humoral-mediated cytotoxicity on isolated rat pancreatic islets by glucose.

Rat islets of Langerhans exposed for 20 h at high glucose (20 mmol/l) to 50% or 20% experimentally raised rabbit anti-rat islet cell surface antiserum (ICSA-positive serum) plus complement exhibited an irreversible loss of glucose-stimulated insulin secretion. In contrast, islets treated with 50% ICSA-positive serum at low glucose (5.5 mmol/l) could overcome this alteration within a subsequent 48 h recovery period at 10 mmol/l glucose in the absence of ICSA, and islets affected at 5.5 mmol/l glucose by 20% ICSA-positive serum even retained the insulin secretory potential and responded on glucose challenge already immediately after the removal of ICSA. The islet insulin content was reduced by the effect of 50% as well as of 20% ICSA-positive serum and complement irrespective of whether the glucose level amounted to 5.5 or 20 mmol/l during serum influence. However, islets altered in a normoglycaemic environment at 5.5 mmol/l glucose by 20% ICSA-positive serum restored their insulin content up to the level of control islets, whereas those islets affected under hyperglycaemic conditions at 20 mmol/l glucose only partially recovered. Thus, beta-cell loss and/or impairment of the insulin secretory mechanisms result from the simultaneous action of humoral-mediated anti-islet cytotoxicity and elevated glucose level, and cause the diminished insulin secretory potential of the islets. These results support the hypothesis that decreasing the insulin secretory activity of beta cells may protect them from cytotoxic immunological attacks.