A possible common cell surface autoantigen in islet beta-cells and thyroid follicular cells in patients with non-insulin dependent diabetes mellitus and chronic thyroiditis.

By an indirect immunofluorescence method with In-111 cells (hamster insulinoma cell line), circulating islet cell surface antibodies (ICSA) were detected in 7 (20%) out of 36 patients with non-insulin dependent diabetes mellitus (NIDDM), 9% of 68 chronic thyroiditis (CT) patients, or 16% of 19 NIDDM patients associated with CT, but not in 18 normal subjects. Sera from five out of nine ICSA-positive patients examined further also showed cell-surface immunofluorescence on TPC-1 cells (human thyroid papillary adenocarcinoma cell line), and prior absorption of the sera with In-111 cells abolished the immunofluorescence. The 64 kDa protein from In-111 cells or human thyroid follicular cells was immunoprecipitated with ICSA-positive sera. In one case of NIDDM associated with CT, 64 kDa protein was detected in both cells. The results indicate that some ICSA in NIDDM patients recognize the same or a very closely-related autoantigen(s) in both islet beta-cells and thyroid follicular cells, suggesting an explanation, at least in part, for the autoimmune mechanism(s) in clinical association of NIDDM and CT.