Ontogeny of islet cell antibodies, insulin autoantibodies and insulitis in the non-obese diabetic mouse

Abstract

The predictive value of insulitis, islet cell cytoplasmic antibodies and insulin autoantibodies for insulin-dependent diabetes was studied in young female non-obese diabetic mice. The ontogeny of the three markers was examined cross-sectionally at days 15, 25, 40 and 90 while islet cell antibodies and insulin autoantibodies were studied longitudinally from day 35 or day 144-168 until approximately day 250. Insulitis was first observed at day 40 (50%) and subsequently at day 90 (70%). Islet cell antibodies and insulin autoantibodies were present at day 15 in 46% and 54% of the animals respectively. The rate of islet cell antibodies was slightly higher at day 25 (60%) than at day 40 (40%) and day 90 (54%) whereas antibodies to insulin were present in all samples from day 25-90. At day 40 and day 90 insulitis and insulin autoantibodies were present together in 42% and 70% of the animals, respectively, while insulitis and islet cell antibodies had a lower rate of concordance (17% and 42%, respectively; diabetes rate, 30%). The concordance rates for islet cell antibodies and insulin autoantibodies were 42% at day 40 and 54% at day 90. Concordance for all three markers was first observed at day 40 (17%) which increased to 38% at day 90. In longitudinal studies, islet cell antibodies and insulin autoantibodies were often present together whether or not diabetes supervened. In the islet cell antibody procedure, immunoreactive cells were shown immunohistochemically to correspond with insulin and/or glucagon cells. However, this staining was not suppressible with insulin- or glucagon- absorbed sera, implying the presence of non-hormonal autoantigens. We conclude that the three markers investigated are expressed early after birth and well before clinical symptoms appear in this animal model. Both islet cell antibodies and insulin autoantibodies preceded insulitis but the prevalence rate for each marker or their degree of concordance was different from the anticipated rate of diabetes in our colony. Consequently, the early expression of the three markers alone is not predictive of diabetes although concordance for the two, or all three markers may be of some value. However, no animal developed diabetes without the prior appearance of both islet cell antibodies and insulin autoantibodies.