THE ROLE OF THE LIPOPHOSPHOGLYCAN OF LEISHMANIA IN VECTOR COMPETENCE

The surface lipophosphoglycans (LPG) of Leishmania promastigotes expre ss stage- and species-specific polymorphisms that are defined by varia tions in the type and number of phosphorylated oligosaccharide repeats . We have studied how these polymorphic structures control the develop ment of transmissible infections in the sandfly vector as well as the species-specificity of vectorial competence. Procyclic promastigotes d isplayed an inherent capacity to bind to midgut epithelial cells of a competent vector. This capacity was lost during their transformation t o metacyclic promastigotes, permitting the selective release and anter ior migration of infective-stage parasites for subsequent transmission by bite. Midgut attachment and release were found to be controlled by developmental modifications in terminally exposed saccharides on LPG, which, depending on the species of Leishmania, involved either substi tution or capping of terminal side-chain sugars, loss of terminal side -chain sugars, substitution or loss of neutral capping sugars. The sta ge-specific terminal sugars involved in midgut adhesion are, in some c ases, also species-specific, and the extent to which these differences affect midgut attachment, forcefully predicted vectorial competence.