Immune complexes in Indian kala-azar.

Patients with Indian kala-azar were investigated for the presence of circulating immune complexes by the platelet aggregation test, complement deviation test, and polyethylene glycol precipitation test. Circulating antibodies were tested by the conventional indirect immunofluorescence test using leptomonad forms of Leishmania donovani and Crithidia luciliae. The serum complement level (C3) was measured using the Mancini technique. The results indicate that a large number of patients with Indian kala-azar carry circulating immune complexes with a significant lowering of complement levels in their sera. These complexes may be intimately linked with the depressed cell-mediated immune responses that are commonly observed in these patients. The study warrants a detailed immunohistopathological examination of the kidneys for the presence of tissue-bound complexes in chronic patients. Further, it is revealed that Crithidia luciliae and Leishmania donovani share common antigens and the former can be used as a substitute for determining anti-leishmania antibody by the indirect fluorescence assay.