Complement mediated bactericidal activity and humoral immune response in type 2 diabetes mellitus

Since diabetic patients suffer from protracted infections, the aim of this study was to determine the functions of serum complement and its relationship with immunoglobulin profiles in patients with type 2 diabetes mellitus (DM). A total of 55 DM patients and 54 healthy volunteers were included in this study. Serum IgG was measured by nephelometry, complement components C3 and C4, and IgA were measured by immunoturbidometric methods. The bactericidal activities of complement from fresh serum and complement-inactivated serum were assessed against Escherichia coli DH5α cells using the standard plate count method. In the DM patients, IgG (p<0.001), IgA (p<0.02) and complement component C4 (p<0.001) were found to be significantly elevated whereas the levels of C3 were slightly lowered (p<0.4). The complement mediated bactericidal activity in diabetic patients was significantly lower than the controls (p<0.01). In contrast, while the serum complements were inactivated by heat treatment, the DM patients had significantly higher (p<0.01) bactericidal activity associated with heat-stable immune effector molecules, possibly elevated levels of serum IgG and IgA. The results of this study indicate that serum complement mediated bactericidal activity was impaired in type 2 diabetic patients, which might be a cause for delayed wound healing and repeated infections. (Int J Diabetes Metab 14: 92-97, 2006)