Subspecies-specific surface antigens of promastigotes of the Leishmania donovani complex.

Sodium dodecyl sulfate-polyacrylamide gel electrophoresis patterns of proteins and externally exposed labeled surface constituents were analyzed in promastigotes of three etiological agents of kala azar (Leishmania donovani, HS70 strain from India; L. chagasi, Imperatriz strain from Brazil; L. infantum, ITMPA K263 strain from Morocco and MO strain from France). Coomassie blue-stained gels showed similar protein patterns for L. donovani and L. chagasi and a more distinct one for L. infantum. Surface radioiodination with two different methods, lactoperoxidase and IODO-GEN, gave identical autoradiographic patterns for each parasite. Four major labeled proteins with apparent Mr values of 65,000, 60,000, 50,000, and 26,000 were detected in both L. chagasi and L. donovani. However, the radioiodinated polypeptide pattern of L. infantum only showed two major bands with an apparent Mr of 62,000 and a doublet of 26,000 to 23,000. Immunoprecipitation of detergent extracts of labeled promastigote subspecies with immune sera from rabbits immunized with either L. chagasi or L. infantum and from patients and mice infected with these two parasites, as well as with a monoclonal antibody against the surface of L. donovani promastigotes, demonstrated that the surface antigenic expression of L. infantum is different from that noticed in the two other subspecies, which are similar. Immunofluorescence experiments with some of these antibodies confirmed these results. The present findings should be considered in taxonomic and immunological studies in visceral leishmaniasis.