Circulating immune complexes and B lymphocytes in diabetic patients with and without microangiopathy.

Circulating immune complexes (CIC) were evaluated in 57 diabetic patients: 28 were insulin-dependent (IDD) and 29 were non insulin-dependent (NIDD) subdivided according to the presence or absence of microangiopathy. The following techniques were used: 1) binding to human red blood cells through C3b complement fraction and posterior radioimmunoassay with 125I labeled anti human IgG (HRBC RIA test); and 2) CIC precipitation with 3.5% polyethylenglycol (PEG test). The percentage of circulating B lymphocytes was evaluated simultaneously in the same patients, using a) direct immunofluorescence techniques (surface IgC cells) and b) cells with complement C3b fraction receptors (EAC rosettes). Twenty normal donors were studied simultaneously as controls. Our results showed that CIC levels were significantly higher in both groups of patients when compared to normal controls. Values for IDD and NIDD were 48.55 +/- 5.97 and 34.68 +/- 3.08 microgram/ml, respectively, for HRBC RIA test and 0.53 +/- 0.07 and 0.41 +/- 0.04 O.D., respectively, for PEG test, while control values were 26.63 +/- 2.12 microgram/ml for HRBC RIA test and 0.26 +/- 0.03 O.D. for PEG test. IDD patients with microangiopathy presented higher CIC levels as measured by HRBC RIA test than IDD without microvascular complications, while no difference was found within the NIDD group. An increase in the proportion of cells bearing surface IgG was observed in IDD and NIDD patients when compared to controls. By contrast, no difference was observed when EAC rosettes-forming cells were evaluated.