Alpha-galactosylceramide as adjuvant induces protective cell-mediated immunity against Leishmania mexicana infection in vaccinated BALB/c mice.

Adjuvants represent a promising strategy to improve vaccine effectiveness against infectious diseases such as leishmaniasis. Vaccination with the invariant natural killer T cell ligand α-galactosylceramide (αGalCer) has been used successfully as adjuvant, generating a Th1-biased immunomodulation. This glycolipid enhances experimental vaccination platforms against intracellular parasites including Plasmodium yoelii and Mycobacterium tuberculosis. In the present study, we assessed the protective immunity induced by a single-dose intraperitoneal injection of αGalCer (2 µg) co-administrated with a lysate antigen of amastigotes (100 µg) against Leishmania mexicana infection in BALB/c mice. The prophylactic vaccination led to 5.0-fold reduction of parasite load at the infection site, compared to non-vaccinated mice. A predominant pro-inflammatory response was observed in challenged vaccinated mice, represented by a 1.9 and 2.8-fold-increase of IL-1ß and IFN-γ producing cells, respectively, in the lesions, and by 23.7-fold-increase of IFN-γ production in supernatants of restimulated splenocytes, all compared to control groups. The co-administration of αGalCer also stimulated the maturation of splenic dendritic cells and modulated a Th1-skewed immune response, with high amounts of IFN-γ production in serum. Furthermore, peritoneal cells of αGalCer-immunized mice exhibited an elevated expression of Ly6G and MHCII. These findings indicate that αGalCer improves protection against cutaneous leishmaniasis, supporting evidence for its potential use as adjuvant in Leishmania-vaccines.

Leishmania mexicana: Novel Insights of Immune Modulation through Amastigote Exosomes.

Exosomes are extracellular microvesicles of endosomal origin (multivesicular bodies, MVBs) constitutively released by eukaryotic cells by fusion of MVBs to the plasma membrane. The exosomes from Leishmania parasites contain an array of parasite molecules such as virulence factors and survival messengers, capable of modulating the host immune response and thereby favoring the infection of the host. We here show that exosomes of L. mexicana amastigotes (aExo) contain the virulence proteins gp63 and PP2C. The incubation of aExo with bone marrow-derived macrophages (BMMs) infected with L. mexicana led to their internalization and were found to colocalize with the cellular tetraspanin CD63. Furthermore, aExo inhibited nitric oxide production of infected BMMs, permitting enhanced intracellular parasite survival. Expressions of antigen-presenting (major histocompatibility complex class I, MHC-I, and CD1d) and costimulatory (CD86 and PD-L1) molecules were modulated in a dose-dependent fashion. Whereas MHC-I, CD86 and PD-L1 expressions were diminished by exosomes, CD1d was enhanced. We conclude that aExo of L. mexicana are capable of decreasing microbicidal mechanisms of infected macrophages by inhibiting nitric oxide production, thereby enabling parasite survival. They also hamper the cellular immune response by diminishing MHC-I and CD86 on an important antigen-presenting cell, which potentially interferes with CD8 T cell activation. The enhanced CD1d expression in combination with reduction of PD-L1 on BMMs point to a potential shift of the activation route towards lipid presentations, yet the effectivity of this immune activation is not evident, since in the absence of costimulatory molecules, cellular anergy and tolerance would be expected.

Leishmania mexicana cell death achieved by Cleoserrata serrata (Jacq.) Iltis: Learning from Maya healers.

ETHNOPHARMACOLOGICAL RELEVANCE: Aerial parts of Cleoserrata serrata (Jacq.) Iltis are widely used in South-Central Mexico to treat wounds and bacterial skin infections and in Panama by Kuna, Ngöbe-Buglé, and Teribe Indians for tropical warm baths and by Kunas in the form of "Ina kuamakalet" for snakebites. AIMS OF THE STUDY: To evaluate the effect of Cleoserrata serrata extract on growth and viability of L. mexicana amastigotes and promastigotes in vitro, as well as on bacteria that usually co-infect skin ulcers. MATERIALS AND METHODS: Cleoserrata serrata was collected in La Chontalpa, Tabasco, Mexico. The antiproliferative effect of the extract was tested on growth of Leishmania mexicana amastigotes and promastigotes in vitro, as well as on bacteria that usually co-infect skin ulcers. RESULTS: Our data show that Cleoserrata serrata significantly inhibits parasite growth (which was more important in infective amastigotes) and additionally inhibits growth of the co-infective bacteria Staphylococcus aureus and Pseudomonas aeruginosa. Confocal microscopy showed a leishmanicidal effect. CONCLUSION: We conclude that Cleoserrata serrata extract is potentially an optimal treatment alternative for patients with cutaneous leishmaniasis infected with Leishmania mexicana, since it controls both the parasite as well as bacterial co-infections. Furthermore, it can be applied topically. The precise metabolites responsible for the anti-Leishmania and anti-bacterial effects remain to be established.