Class-specific immunoglobulins and antibodies to mycobacterial sonicates and autoantigens in leprosy patients and contacts.

A comprehensive analysis of the humoral immune response in leprosy patients and contacts was undertaken. Class-specific antibodies to four mycobacterial sonicates, three autoantigens and three haptens were estimated by ELISA. It was found that IgG levels varied more extensively than IgM or IgA and that total serum IgG was significantly higher in lepromatous bacterial index positive (LL+ve) and negative LL-ve) leprosy patients than in tuberculoid (TT/BT) patients and controls. The high levels of anti-mycobacterial antibodies found in untreated LL+ve patients were significantly reduced in LL-ve patients after effective chemotherapy. Considerable amount of anti-mycobacterial IgG was also detected in TT/BT patients. Each serum when assayed against sonicates of Mycobacterium leprae, Mycobacterium tuberculosis, ICRC bacilli and BCG gave a similar antibody profile suggesting that these antibodies were directed predominantly against cross-reactive antigens. Up to 75% of LL patients and 35% of TT/BT patients were found to be positive for antibodies to histone, collagen and fibronectin. However, antibodies to several haptens were not detected in any of the patients and controls studied. Taken together, these results suggested that the amount of IgG antibodies is directly correlated with the antigenic load in the system, and that there is no evidence for polyclonal activation. It may be speculated that the regulatory mechanism of antibody production is severely deranged in lepromatous leprosy patients.