Surface antigen profiles of Leishmania donovani promastigote isolates have been studied. Surface patterns of Brazilian and African isolates display remarkable similarities and are extremely simple, consisting of three major peptides of 65,000, 25,000, and 23,000 mol wt. Surface iodination and biosynthetic labeling coupled to immunoprecipitation techniques revealed that a single major determinant of 65,000 mol wt is recognized in all strains by sera from kala-azar patients from both Brazil and Africa. This major determinant is not brought down by sera from normal individuals and shows no significant cross-reactivity with sera from Chagas' disease, leprosy, or syphilis patients. Binding to concanavalin A suggests a glycoprotein nature for this antigen. Sera from patients with cutaneous leishmaniasis (L. braziliensis) also recognized the same 65,000-mol wt determinant, although to a lesser extent. The possibility that this major surface antigen is shared, with minor differences, not only by L. donovani strains but between Leishmania species in general is suggested.

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