Presentation of the Leishmania antigen LACK by infected macrophages is dependent upon the virulence of the phagocytosed parasites

Abstract

We have previously demonstrated that murine macrophages (Mphi) infected with Leishmania promastigotes, in contrast to Mphi infected with the amastigote stage of these parasites, are able to present the Leishmania antigen LACK (Leishmania homologue of receptors for activated C kinase) to specific, I-Ad-restricted T cell hybrids and to the T cell clone 9.1-2. These T cells react with the LACK (158-173) peptide, which is immunodominant in BALB/c mice. Here, we show that the level of stimulation of the LACK-specific T cell hybridoma OD12 by promastigote-infected Mphi is clearly dependent upon the differentiation state of the internalized parasites. Thus, shortly after infection with log-phase or stationary-phase promastigotes of L. major or of L. amazonensis, Mphi strongly activated OD12. The activity was transient and rapidly lost. However, under the same conditions, activation of OD12 by Mphi infected with metacyclic promastigotes of L. major or of L. amazonensis was barely detectable. At the extreme, Mphi infected with amastigotes were incapable to stimulate OD12. Thus, the presentation of LACK by infected Mphi correlates with the degree of virulence of the phagocytosed parasites, the less virulent being the best for the generation/expression of LACK (158-173)-I-Ad complexes. While the intracellular killing of the parasites appears to be an important condition for the presentation of LACK, it is not the only requisite. The partial or total destruction of intracellular L. amazonensis amastigotes does not allow the presentation of LACK to OD12. A preferential interaction of LACK (158-173) with recycling rather than newly synthesized MHC class II molecules does not explain the transient presentation of LACK by Mphi infected with log-phase or stationary-phase promastigotes because brefeldin A strongly inhibited the presentation of LACK to OD12. Taken together, these results suggest that virulent stages of Leishmania, namely metacyclics and amastigotes, have evolved strategies to avoid or minimize their recognition by CD4+ T lymphocytes.

Mechanisms of Immune Evasion in Leishmaniasis

“…Studies on presentation of the Leishmania antigen, Leishmania homolog of receptors for activated C kinase (LACK), by infected macrophages showed a transient yet strong LACK-specific T cell response when infected with stationary or log phase Leishmania promastigotes. On the other hand, murine macrophages infected with either Leishmania metacyclic promastigotes or amastigotes showed a weak or absent LACK-specific T cell activation respectively (Courret et al, 1999). Membrane lipid rafts are important platforms for antigen presentation as it concentrates MHC class II molecules into microdomains, which allow efficient antigen presentation at low peptide densities.…”

Persistence of Lesions in Suppressor of Cytokine Signaling-1-Deficient Mice Infected with Leishmania major

“…The culture conditions have been described previously (20). Metacyclic promastigotes were isolated by negative selection with peanut agglutinin (Vector Laboratories, Burlingame, CA) as previously described (21).…”

Low and high-dose intradermal infection with Leishmania majorand Leishmania amazonensis in C57BL/6 mice

“…L. amazonensis replicates in the gut of flies of the genus Lutzomia and there it differentiates into a metacyclic, infective parasite (Lainson et al 1987). Infective parasites express different carbohydrates on their surface than do non-infective forms (Saraiva et al 1986, Courret et al 1999. Parasites reach the vertebrate host when the fly feeds on the host's blood and regurgitates parasites present in the mouth or adjacent posterior regions (Killick-Kendrick 1990).…”

“…Once in the vertebrate host, Leishmania metacyclic promastigotes interact with macrophages through ligand receptor-mediated residues on their surfaces and mannose receptors on the macrophage surface (Mosser et al 1987, Da Silva et al 1989. Metacyclic promastigotes interact with macrophages differently than non-infective forms (Courret et al 1999, Saraiva et al 2005 and they have been shown to impair the capacity of macrophages to present antigens (Courret et al 1999). However, most studies use stationary phase cultures, which contain mostly (80%) non-infective forms, for experimental infections (Scott 1989, da Costa et al 1992, Afonso & Scott 1993, Santiago et al 1999, Ji et al 2003.…”

“…Stationary phase cultures of L. amazonensis contain a mixture of procyclic and metacyclic promastigotes (Courret et al 1999). Hence, when injected with high numbers of stationary phase parasites, mice are exposed to both infective and non-infective forms.…”