Serum capacity to solubilize immune complexes (ICSC) in patients with insulin-dependent diabetes mellitus

Immune complex solubilizing capacity (ICSC) of sera obtained from patients with insulin-dependent diabetes mellitus (IDDM) was assayed by the spectrophotometric method. In 17/32 IDDM sera, ICSC was significantly low. The value of ICSC was only weakly correlated with serum CH50 (r = 0.42). Six sera out of 28 showed a high serum immune complex level and low ICSC. The results with these 6 cases suggest the possibility that circulating antigen-antibody complex might be insoluble in vivo. The precise characterization of these 6 patients' autoantibodies was obtained with immunofluorescence tests. Interestingly, 2 of these sera were positive for islet cell surface antibodies (ICSA) and AtT-20 cell (ACTH secreting cell) surface antibodies.