IgG humoral response against the antigen 85 complex homologues in leprosy.

Antigen 85 complex is the major protein component present in M. bovis BCG culture filtrate (CF). It consists of a family of three proteins: 85A, 85B and 85C. Combining isoelectric focusing and Western blot analysis, we have previously identified different antigenically related proteins present in the CF of other mycobacteria (M. tuberculosis, M. kansasii, M. avium, M. gordonae, M. fortuitum and M. phlei) using monoclonal antibodies (MoAbs) directed against the antigen 85 complex of M. bovis BCG. Humoral immune response directed against these cross-reactive homologues was analysed in sera from 20 patients with multibacillary leprosy (BL/LL), from 20 patients with paucibacillary leprosy (BT/TT) and from 15 healthy leprosy contacts. All the antigen 85 homologues identified in the seven CFs by MoAbs were also recognized by IgG present in sera from multibacillary leprosy patients, but not or very faintly in sera from paucibacillary leprosy patients or from healthy subjects. These results suggest that some of the M. leprae epitopes inducing a significant humoral response in multibacillary leprosy are common to the various 85 antigenically related proteins present in all mycobacterial species.