Dependence of Antigen Expression on Functional State of β-Cells

Antigen expression corresponding to anti-islet cell surface monoclonal antibodies IC2 and A2B5 was studied. IC2 is a rat-rat hybridoma autoantibody produced from the BB rat; among islet cells, IC2 is β-cell specific. A2B5 is an anti-ganglioside antibody described as labeling β-cells. Islets of Langerhans from Lewis rats were isolated and cultured for 18 h in RPMI-1640 with five different glucose concentrations (2.2, 3.3, 5.5, 11.1, and 18.3 mM). In some experiments, islets were precultured for 2 or 3 days. After isolation of islet cells and antibody labeling, the percent of IC2⁺ β-cells in the different groups increased from 33.3, 34.5, 40.9, and 57.2 to 58.6% (P < 10⁻⁶). For A2B5, the percent of labeled islet cells increased from 37.4, 41.8, 46.7, and 53.8 to 56.2% (P < 10⁻⁴). Thus, increasing glucose concentration leading to higher β-cell activity implies an increase in antigen expression. Neither A2B5 nor IC2 reacts with insulin, as shown by absorption experiments and immune electron microscopy of binding sites. Electron microscopy of IC2-gold-labeled islet cells substantiated the β-cell specificity of IC2. In conclusion, expression of the corresponding antigens to IC2 and A2B5 depends on the functional state of the β-cells; because this has been shown to be an important factor in the development of insulin-dependent diabetes, our findings may be of potential pathogenetic interest.