Complement activation in diabetes mellitus

To see whether or not there is complement activation in patients with diabetes mellitus, we investigated the plasma concentrations of C4, C3, C4a, C3a and SC5b-9 in either juvenile or adult onset insulin-dependent (IDDM) and noninsulin-dependent (NIDDM) diabetic patients at least 2 years after diagnosis. C4, C3, SC5b-9 plasma levels were not significantly different in IDDM and NIDDM patients than in age-matched controls. Anaphylatoxin peptide conversion product C4a, but not C3a, was found significantly higher in adult-onset IDDM patients than in patients with juvenile onset IDDM, NIDDM patients and age-matched controls. Complement activation did not appear to be correlated with the metabolic control, nor the duration of disease nor the presence of circulating antibodies (including islet cells (ICA), insulin (IA), thyroid microsomal (TMA), and thyroglobulin (TGA)). Although there are many factors that may trigger complement activation, we found the highest levels of C4a in elderly subjects (both diabetics and control subjects) and particularly in those who had clinically detectable vascular complications.