EVIDENCE THAT THE VECTORIAL COMPETENCE OF PHLEBOTOMINE SAND FLIES FORDIFFERENT SPECIES OF LEISHMANIA IS CONTROLLED BY STRUCTURAL POLYMORPHISMS IN THE SURFACE LIPOPHOSPHOGLYCAN

Phlebotomine vectors can in some instances transmit only certain speci es of Leishmania. Comparison of a large number of vector/parasite pair s revealed that species-specific differences in vectorial competence w ere in every case directly correlated with the ability of promastigote s to attach to the sand-fly midgut, the variable outcomes of which wer e controlled by structural polymorphisms in the surface lipophosphogly can (LPG) of the parasite. The ability of Phlebotomus papatasi to tran smit only Leishmania major could be attributed to the unique, highly s ubstituted nature of L. major LPG that provides for multiple terminall y exposed beta-linked galactose residues for binding. While the relati vely unsubstituted LPGs of other Leishmania species were unable to med iate promastigote attachment to P. papatasi, they could mediate bindin g to midguts of Phlebotomus argentipes, which was found to be a potent ially competent vector for every Leishmania species examined. The data suggest that at least some phlebotomine vectors differ with respect t o the parasite recognition sites which they express and that midgut ad hesion is a sufficiently critical component of vectorial competence as to provide the evolutionary drive for LPG structural polymorphisms.