Characterization of mycobacterial antigens and antibodies in circulating immune complexes from pulmonary tuberculosis

Circulating immune complexes (CICs) in serum samples from patients with pulmonary tuberculosis (bacteriologically positive [S+C+] and bacteriologically negative [S-C-]) and controls (NHC) have been measured by using C1q binding assay (C1qBA) and 3.5% polyethylene glycol precipitation and measurement of absorbance at 280 nm (PEG-OD 280). Although C1qBA did not show any difference between tuberculous and normal serum samples, PEG-OD 280 was significantly elevated in tuberculous samples. The effect of chemotherapy on CIC levels was studied. During the treatment, initially (for up to 2 months) there was a rise in CIC levels and later a fall, coinciding with bacterial clearance. Anti-purified protein derivative antibodies of class immunoglobulin G (IgG) and immunoglobulin M were measured in the serum samples and PEG precipitates. Anti-mycobacterial antibody measurement in CICs was more discriminatory between the groups than serum antibody. For characterization of the complexed antibody, the PEG precipitates were used in the Western blot and the patterns were compared. S+C+ CICs contained antibodies for a wide range of antigens ranging from 100 Kd to 10 Kd. However, none of the NHC-CICs contained antibodies for antigens < 70 Kd. Thus, when using the criterion of positivity for antibodies to antigens < 70 Kd as a marker for pulmonary tuberculosis, 24 of 24 (100%) of the S+C+ CICs were positive. Similarly, 11 of 16 (70%) of the S-C- CICs contained antibodies for antigens < 70 Kd.(ABSTRACT TRUNCATED AT 250 WORDS)