Binding of Leishmania infantum Lipophosphoglycan to the Midgut Is Not Sufficient To Define Vector Competence in Sand Flies.

The major surface lipophosphoglycan (LPG) of parasites is critical to vector competence in restrictive sand fly vectors in mediating attachment to the midgut epithelium, considered essential to parasite survival and development. However, the relevance of LPG for sand flies that harbor multiple species of remains elusive. We tested binding of wild-type (WT), LPG-defective (Δ mutants), and add-back (Δ+) lines to sand fly midguts and their survival in sand flies WT parasites attached to the midgut , with late-stage parasites binding to midguts in significantly higher numbers than were seen with early-stage promastigotes. Δ mutants did not bind to midguts, and this was rescued in the Δ+ lines, indicating that midgut binding is mediated by LPG. When sand flies were infected with the WT or Δ or Δ+ line of the BH46 or BA262 strains, the BH46 Δ mutant, but not the BA262 Δ mutant, survived and grew to numbers similar to those seen with the WT and Δ+ lines. Exposure of BH46 and BA262 Δ mutants to blood-engorged midgut extracts led to mortality of the BA262 Δ but not the BH46 Δ parasites. These findings suggest that LPG protects parasites on a strain-specific basis early in infection, likely against toxic components of blood digestion, but that it is not necessary to prevent evacuation along with the feces in the permissive vector It is well established that the presence of LPG is sufficient to define the vector competence of restrictive sand fly vectors with respect to parasites. However, the permissiveness of other sand flies with respect to multiple species suggests that other factors might define vector competence for these vectors. In this study, we investigated the underpinnings of survival and development in its natural vector, We found that LPG-mediated midgut binding persists in late-stage parasites. This observation is of relevance for the understanding of vector-parasite molecular interactions and suggests that only a subset of infective metacyclic-stage parasites (metacyclics) lose their ability to attach to the midgut, with implications for parasite transmission dynamics. However, our data also demonstrate that LPG is not a determining factor in retention in the midgut of , a permissive vector. Rather, LPG appears to be more important in protecting some parasite strains from the toxic environment generated during blood meal digestion in the insect gut. Thus, the relevance of LPG in parasite development in permissive vectors appears to be a complex issue and should be investigated on a strain-specific basis.