Immune complexes and antibodies to BCG in sera from patients with mycobacterial infections

We have examined the prevalence of circulating immune complexes in sera from patients with mycobacterial infection. Sera from 68% of patients with active M. tuberculosis and 58% of patients with M. intracellulare infections had significantly elevated C1q binding activity (C1q-BA). In general there was a fall in C1q-BA with treatment. Only 15% of M. tuberculosis patients with a bacteriological cure, 22% of non-tubercular patients with chronic obstructive pulmonary disease, and 3% of normal individuals had an elevated C1q-BA. Antibodies to a BCG-derived antigen were demonstrated in most of the individuals studied in all groups but significantly elevated levels were seen only in patients with mycobacterial infections. In certain patients there appeared to be an inverse relationship between C1q-BA and BCG binding, suggesting that perhaps BCG-related antigens participated in the immune complexes found. Other possible antigen-antibody complexes are discussed.