Characterization of circulating immune complexes in leprosy patients and their correlation with specific antibodies against Mycobacterium leprae.

Circulating immune complex (CIC) levels and their antibody and antigenic composition were evaluated in patients with leprosy as well as in any individuals living with them; they were precipitated with 3.5% polyethylene glycol (PEG) and, after affinity chromatography isolation and purification, analysed by sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) and immunoblot with monoclonal antibodies (Mabs). The presence of CICs was demonstrated throughout the clinical and immunopathological leprosy spectrum at levels related to bacterial load, and in leprosy patients they showed a positive correlation with specific anti-PGL and anti-65 kDa antibodies. The isolation and analysis, however, failed to identify any Mycobacterium leprae antigenic components; although two specific antibodies anti-PGL-1 and anti-65 kDa were identified as possible CIC constituents and may be potentially useful in the follow-up of leprosy patients, especially to check bacterial load evolution, PGL-1 being an authentic antigen of this mycobacterium. Also, the involvement of 65 kDa in CICs, being homologous with the human heat shock protein (HSP) 60 kDa family, suggests an autoimmune mechanism in leprosy pathogenesis. Furthermore, those results support the inclusion of CIC antibody reactivity studies to enhance the sensitivity of serology.