Islet cell surface antibodies (ICSAs) in sera of New Zealand Black (NZB) and New Zealand White (NZW) mice were detected by the indirect immunofluorescence method with cultured Balb/c mouse islet cells as antigens. Circulating ICSAs appeared in NZB mice from age 20 wk; at 30 wk, 73% of male mice and 88% of female mice had detectable ICSAs. The ICSAs were significantly absorbed with mouse islet cells but hardly absorbed with spleen cells or liver powder. The ICSAs also bound with islet cells of ICR mice, Sprague-Dawley rats, and NZB mice. NZB mice showed glucose intolerance especially at ages 10 and 30 wk. Although plasma glucose levels tended to be higher in NZB mice with strongly positive ICSAs, pancreatic insulin content was not reduced, and insulitis was rarely observed in the pancreases. On the other hand, 30-wk-old NZW mice had normal or mildly impaired glucose tolerance and only weak, if any, ICSAs. The ICSA-positive serum of NZB mice significantly suppressed glucose-induced insulin release by cultured islet cells. The ICSAs may be responsible, at least in part, for glucose intolerance in NZB mice after age 20 wk through the inhibitory effect on insulin secretion,

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