Cloning of a gene encoding the immunodominant surface antigen of Leishmania donovani promastigotes.

This study describes the characterisation of externally oriented surface peptides of both morphological forms of Leishmania donovani, the causative agent of visceral leishmaniasis (kala-azar). Using 125I surface labelling techniques and peptide extraction in the detergents Triton X-100 and Triton X-114, a major iodinable promastigote peptide at 63 kDa or 65 kDa (depending on detergent used) was identified. This peptide was demonstrated to be the immunodominant membrane peptide of L. donovani and was strongly recognised by human sera from parasitologically confirmed cases of kala-azar. This peptide was not demonstrated on the surface of tissue amastigotes, although in vitro translations of poly(A+) RNA from both promastigotes and amastigotes demonstrated that both forms possessed mRNA that directs the synthesis of a 63 kDa peptide. It is suggested therefore that in amastigotes this peptide may be a processed antigen. We also report the isolation of a recombinant cDNA clone in the bacteriophage vector lambda gt10 which encodes a 63 kDa polypeptide that is recognised by human kala-azar sera. It is proposed that this surface peptide could be used in a specific immunodiagnostic test for leishmaniasis.