Caspar-like gene depletion reduces Leishmania infection in sand fly host Lutzomyia longipalpis.

Female phlebotomine sand flies Lutzomyia longipalpis naturally harbor populations of the medically important Leishmania infantum (syn. Leishmania chagasi) parasite in the gut, but the extent to which the parasite interacts with the immune system of the insect vector is unknown. To investigate the sand fly immune response and its interaction with the Leishmania parasite, we identified a homologue for caspar, a negative regulator of immune deficiency signaling pathway. We found that feeding antibiotics to adult female L. longipalpis resulted in an up-regulation of caspar expression relative to controls. caspar was differentially expressed when females were fed on gram-negative and gram-positive bacterial species. caspar expression was significantly down-regulated in females between 3 and 6 days after a blood feed containing Leishmania mexicana amastigotes. RNA interference was used to deplete caspar expression in female L. longipalpis, which were subsequently fed with Leishmania in a blood meal. Sand fly gut populations of both L. mexicana and L. infantum were significantly reduced in caspar-depleted females. The prevalence of L. infantum infection in the females fell from 85 to 45%. Our results provide the first insight into the operation of immune homeostasis in phlebotomine sand flies during the growth of bacterial and Leishmania populations in the digestive tract. We have demonstrated that the activation of the sand fly immune system, via depletion of a single gene, can lead to the abortion of Leishmania development and the disruption of transmission by the phlebotomine sand fly.

EST sequencing of blood-fed and Leishmania-infected midgut of Lutzomyia longipalpis, the principal visceral leishmaniasis vector in the Americas.

Leishmaniasis is an important worldwide public health problem. Visceral leishmaniasis caused by Leishmania infantum chagasi is mainly transmitted by Lutzomyia longipalpis in the Americas. Leishmania development within the sand fly vector is mostly restricted to the midgut. Thus, a comparative analysis of blood-fed versus infected midguts may provide an invaluable insight into various aspects of sand fly immunity, physiology of blood digestion, and, more importantly, of Leishmania development. To that end, we have engaged in a study to identify expressed sequenced tags (ESTs) from L. longipalpis cDNA libraries produced from midguts dissected at different times post blood meal and also after artificial infection with L. i. chagasi. A total of 2,520 ESTs were obtained and, according to the quality of the sequencing data obtained, assembled into 378 clusters and 1,526 individual sequences or singletons totalizing 1,904 sequences. Several sequences associated with defense, apoptosis, RNAi, and digestion processes were annotated. The data presented here increases current knowledge on the New World sand fly transcriptome, contributing to the understanding of various aspects of the molecular physiology of L. longipalpis, and mechanisms underlying the relationship of this sand fly species with L. i. chagasi.