A new model of progressive visceral leishmaniasis in hamsters by natural transmission via bites of vector sand flies

Live attenuated Leishmania donovani p27 gene knockout parasites are nonpathogenic and elicit long-term protective immunity in BALB/c mice

Leishmaniasis causes significant morbidity and mortality worldwide, and no vaccines against this disease are available. Previously, we had shown that the amastigote-specific protein p27 (Ldp27) is a component of an active cytochrome c oxidase complex in Leishmania donovani and that upon deletion of its gene the parasite had reduced virulence in vivo. In this study, we have shown that Ldp27(-/-) parasites do not survive beyond 20 wk in BALB/c mice and hence are safe as an immunogen. Upon virulent challenge, mice 12 wk postimmunization showed significantly lower parasite burden in the liver and spleen. When mice were challenged 20 wk postimmunization, a significant reduction in parasite burden was still noted, suggesting long-term protection by Ldp27(-/-) immunization. Immunization with Ldp27(-/-) induced both pro- and anti-inflammatory cytokine responses and activated splenocytes for enhanced leishmanicidal activity in association with NO production. Protection in both short- and long-term immunized mice after challenge with the wild-type parasite correlated with the stimulation of multifunctional Th1-type CD4 and CD8 T cells. Adoptive transfer of T cells from long-term immunized mice conferred protection against virulent challenge in naive recipient mice, suggesting involvement of memory T cell response in protection against Leishmania infection. Immunization of mice with Ldp27(-/-)also demonstrated cross-protection against Leishmania major and Leishmania braziliensis infection. Our data show that genetically modified live attenuated Ldp27(-/-) parasites are safe, induce protective immunity even in the absence of parasites, and can provide protection against homologous and heterologous Leishmania species.

Animal models for the analysis of immune responses to leishmaniasis

This unit focuses on the murine model of cutaneous leishmaniasis and models of visceral leishmaniasis in mice and hamsters. Each basic protocol describes the methods used to inoculate parasites and to evaluate infections with regard to lesion progression and visceralization, and quantification of parasite load. Five support protocols are provided; two for the growth and isolation of metacyclic promastigotes from in vitro culture, one for isolation of tissue amastigotes from infected animals, one for cryopreservation of parasites, and one for the preparation of blood agar plates for quantitation of parasite numbers in infected tissue.