Not only quantitative but also qualitative changes of serum immunoglobulins in diabetes mellitus.

To extend previous observations on the quantitative changes of IgA and other serum Ig in diabetics, additional immunochemical investigations were carried out in 96 patients, 63 males and 33 females, mean age 43.5 +/- 15.7 years, 51 with type 1 (insulin-dependent) and 45 with type 2 (non-insulin-dependent) diabetes. The immunological data were correlated with the clinical-metabolic aspects. In the whole group, the IgA level was increased (144.1 +/- 57.2 I.U.). Significant differences were recorded with respect to age for IgG, to age and diabetes type for IgA, to sex for IgM. Qualitative Ig changes, reflecting disturbances of molecular structure, mainly for IgG, seldom for IgM, but never for IgA, were observed in 20% of the patients with both types of diabetes, more seldom in cases with long disease duration. The IgG with qualitative changes were purified and their functional capacity of inhibiting the natural cytotoxic activity (NK) was tested in comparison with that induced by pretreatment of the effectory cells with normal IgG. Some of these modified IgG showed a reduced capacity of inhibiting the NK activity. These data confirm the existence of certain quantitative changes of the main serum Ig in diabetics and reveal the presence of qualitative disorders of the IgG molecules, with consequences on their functionality.