CHARACTERIZATION OF MYCOBACTERIAL ANTIGENS AND ANTIBODIES IN CIRCULATING IMMUNE-COMPLEXES FROM PULMONARY TUBERCULOSIS

Circulating immune complexes (CICs) in serum samples from patients wit h pulmonary tuberculosis (bacteriologically positive [S+C+] and bacter iologically negative [S-C-]) and controls (NHC) have been measured by using Clq binding assay (C1qBA) and 3.5% polyethylene glycol precipita tion and measurement of absorbance at 280 nm (PEG-OD 280). Although C1 qBA did not show any difference between tuberculous and normal serum s amples, PEG-OD 280 was significantly elevated in tuberculous samples. The effect of chemotherapy on CIC levels was studied. During the treat ment, initially (for up to 2 months) there was a rise in CIC levels an d later a fall, coinciding with bacterial clearance. Anti-purified pro tein derivative antibodies of class immunoglobulin G (IgG) and immunog lobulin M were measured in the serum samples and PEG precipitates. Ant i-mycobacterial antibody measurement in CICs was more discriminatory b etween the groups than serum antibody. For characterization of the com plexed antibody, the PEG precipitates were used in the Western blot an d the patterns were compared. S+C+ CICs contained antibodies for a wid e 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 t he criterion of positivity for antibodies to antigens <70 Kd as a mark er for pulmonary tuberculosis, 24 of 24 (100%) of the S-C+ CICs were p ositive. Similarly, 11 of 16 (70%) of the S-C- CICs contained antibodi es for antigens <70 Kd. The results are promising that measurement of complexed IgG for mycobacterial antigens of molecular weight <70 Kd mi ght prove to be useful in accurately discriminating between the tuberc ulous patients and endemic normal subjects (100% sensitivity and 100% specificity). Moreover, the test can also be very useful in borderline positive (smear negative) cases, for which group diagnosis is very di fficult. Such a test will be extremely useful in extrapulmonary and ch ildhood tuberculosis, where early diagnosis is needed.