The purification and identification of circulating immune complexes in tuberculosis.

Circulating immune complexes (CIC) have been documented in patients with tuberculosis. Like most other disease-related CIC, the composition of CIC in tuberculosis is unknown. Using the new technique of conglutinin affinity chromatography, we isolated and purified CIC from 6 patients with mycobacterial disease and compared these with CIC from 6 patients with other disorders. The CIC material from both groups was found by Ouchterlony analysis to be similar, containing IgG, IgA, and variable amounts of Clq, C3, and C4. Relative purity was confirmed by the absence of other serum components such as fibrinogen, alpha 1-antiprotease, alpha 2-macroglobulin, and transferrin; trace amounts of albumen were present in all samples. On sucrose density ultracentrifugation, CIC material from both groups demonstrated a well-defined major peak in the 9S to 12S range and a much smaller peak at 7S. After dissociation of CIC at pH 2.8, only a broad band in the 7S region was noted. Ouchterlony analysis demonstrated a positive precipitation reaction between CIC and rabbit anti-BCG in 5 of 6 patients with tuberculosis and 1 of 6 patients without tuberculosis. Anti-BCG activity was demonstrated by precipitation inhibition in 5 of 6 tuberculous and 2 of 6 nontuberculous samples. In all but one of the tuberculous samples tested, these reactions were confined to the 9S to 12S fraction. We conclude that some of the CIC found in patients with tuberculosis are composed of immunoglobulin, complement, and antigen derived from Mycobacterium tuberculosis.