ANTIINSULIN ACTIVITY IN NORMAL NEWBORN CORD-BLOOD SERUM - ABSENCE OF IGG-MEDIATED INSULIN BINDING

Insulin autoantibodies (IAAs) are present in similar to 60% of type I diabetes patients at onset and are used as predictors for the disease. Although the prevalence of IAAs in the general population has been re ported to be <1%, preliminary data have pointed out a higher proportio n of IAA positivity in newborn cord-blood serum, and some authors have suggested that they are immunoglobulin G antibodies, resulting from a hypothetical gestational insulitis. To characterize this insulin-bind ing activity, we analyzed cord-blood sera from 100 healthy newborns, a s well as serum from 21 of their mothers at delivery, 179 new-onset ty pe I diabetic patients, and 200 healthy control subjects. IAAs were pr esent in 0.5% of the control subjects and 54% of new-onset type I diab etic patients. On the other hand, 96% of the newborn cord-blood sera s howed anti-insulin activity, while it was detected in only 14% of thei r mothers. No significant differences were observed between cord sera and the general population for islet-cell or anti-GAD autoantibodies. Anti-insulin activity in cord serum was not bound by protein A or prot ein G, in contrast with type I diabetes-related IAA activity. We concl ude that this insulin-binding activity, present in most newborn cord s era and specific to the child, is not IgG mediated. These data, togeth er with the absence of other pancreatic autoimmunity markers in this p opulation, suggest that it is an isolated phenomenon not related to ty pe I diabetes or other pancreatic autoimmune processes and is due to t he presence of a cross-reacting molecule in cord blood that has yet to be identified.