Centrin-Deleted Leishmania donovani Parasites Help CD4+ T Cells to Acquire Th1 Phenotype and Multi-Functionality Through Downregulation of CD200–CD200R Immune Inhibitory Axis

Abstract

The protozoan parasite Leishmania has evolved several strategies to undermine host defense mechanisms by inducing Th2-type adaptive immunity and suppressing effector functions of Th1 phenotype. In our earlier studies, using centrin gene-deleted Leishmania (LdCen−/−) parasites as an immunogen, we have shown induction of an effective Th1-type immunity and robust memory responses that mediate protection against virulent challenge. However, role of inhibitory signals in Leishmania vaccine induced immunity in general, and LdCen−/− in particular has not been studied. Herein, we report that immunization with LdCen−/− parasites produces more functional Th1-type CD4+ T cells via downregulation of CD200–CD200R immune inhibitory axis compared to wild-type infection. We found that expression of CD200 and CD200R was significantly reduced in LdCen−/− infection compared to wild-type infection. Diminished CD200–CD200R signaling in LdCen−/− infection enabled proliferation of CD4+ T cells and resulted in the induction of pro-inflammatory cytokines and suppression of anti-inflammatory response. The effects of diminished CD200–CD200R signaling by LdCen−/− were most evident in the suppression of IL-10-producing CD4+ T cells that helped enhance more Th1 cytokine producing and multi-functional T cells compared to wild-type infection. In vivo blocking of CD200 expression with anti-CD200 treatment in wild-type infected mice limited Th2 response as indicated by reduction of IL-10-producing Tr1 cells and reduced parasite burden. On the other hand, treatment with anti-CD200 improved the LdCen−/− vaccine-induced multifunctional response and reduction in splenic parasite load upon challenge. Taken together, these studies demonstrate the role of CD200–CD200R signals in the protection induced by LdCen−/− parasites.

Leishmania mexicana Centrin Knock out Parasites Promote M1-polarizing Metabolic Changes

“…We have previously observed critical differences in the immunological responses following inoculation with LmexCen −/− parasites compared to their wild type counterparts 12 . This was also observed in L. donovani, L. major , and L. mexicana centrin mutants 10,12,32,33 . In this study, we explored the metabolic drivers of the immunological differences between infection with the parental or mutant strains and demonstrated that immunization with LmexCen −/− parasites results in unique metabolic changes, compared to naïve and Lmex WT infected mice.…”

Leishmania mexicana centrin knockout parasites promote M1-polarizing metabolic changes

“… 12 This was also observed in L. donovani , L. major , and L. mexicana centrin mutants. 10 , 12 , 42 , 43 Immunization with LmCen −/− and LmexCen −/− has been shown to confer protection against homologous and heterologous challenges. 10 , 11 , 12 , 13 , 44 However, the immune mechanisms of protection differed in these two immunization regimens.…”

Adjuvantation of whole-killed Leishmania vaccine with anti-CD200 and anti-CD300a antibodies potentiates its efficacy and provides strong protection against virulent parasites

“…In addition, the protective response of vaccine candidates, which have been evaluated in both, experimental and human leishmaniasis, has also been linked with the production of pro-inflammatory cytokines in vaccinated individuals 17,20 . Further, the multifunctional antigen experienced CD4 + T cells is an important determinant of disease resistant as well 30,42,43 . The multifunctional nature of the CD4 + T cells not only helps the host to combat infection efficiently but also plays a significant role in the early conversion of effector T cells to their memory phenotypes 31,44 .…”

“…Our recent findings revealed that parasite upregulates the expression of immune inhibitory receptors viz., CD200, CD200R, and CD300a on the surface of macrophages and dendritic cells to dampen their effector properties for survival and proliferation 30,31,32 . Further, the abrogation of CD200R and CD300a signals in L. donovani infected animals was associated with the early elimination of parasites from their visceral organs that was found correlated with the increased functionality of antigen experienced CD4 + and CD8 + T cells 31,32 .…”