Lipid and Lipopolysaccharide‐Like Antigens of Leishmania Promastigotes

Extraction of whole promastigotes of Leishmania tropica major and L. donovani with a mixture of hexane and isopropanol (3:2) yielded three fractions containing immunological activity: 1) lipids, where the activity was determined by radioimmunoassay; 2) a lipopolysaccharide‐like (LPS‐like), water‐soluble precipitate, where activity was determined both by radioimmunoassay and double gel diffusion, and 3) the phenol: water extract of the lipid‐free promastigotes, where activity was followed by double gel diffusion. The use of a solid state, lipid‐based radioimmunoassay for detection of leishmanial antigens provided a sensitive measure of their activity with a considerable degree of species and serotype specificity. We found antibodies to leishmanial lipids in sera from immunized rabbits, convalescent mice, and human patients with confirmed cases of cutaneous leishmaniasis or kala azar. There was very little activity in normal human or animal sera. Analysis by SDS‐polyacrylamide gel electrophoresis of fractions from promastigotes surface‐labeled with galactose oxidase and sodium borotritiate and preliminary immunochemical characterization of the LPS‐like antigen showed that it contained galactose, but otherwise differed immunologically and chemically from excreted factor (EF), the best characterized leishmanial antigen.