Cutaneous leishmaniasis caused by Leishmania mexicana is associated with an important inflammatory response. We here analysed the kinetics of Th17 cells and neutrophils in ear lobe lesions caused by Leishmania mexicana throughout 90 days of disease progression in susceptible BALB/c and semi-resistant C57BL/6 mice infected with 1 × 10 Leishmania mexicana promastigotes. Cells in the lesions were extracted and quantified by flow cytometry, whereas their distribution in the tissues in relation to the parasites was analysed by immunohistochemistry. Our results show that in BALB/c mice, both Th17 cells and neutrophils increase concomitantly and to significantly higher levels on day 90 post-infection, as compared to C57BL/6 mice. Our results provide novel evidence on the cells causing chronic inflammation throughout Leishmania mexicana infections, resulting as a consequence of neutrophil recruitment together with Th17 cell differentiation and recruitment, both of which remain in the infection site throughout the late phase of the infection. We conclude that the more enhanced levels of Th17 cells and neutrophils during chronic inflammatory lesions in BALB/c mice participate in their enhanced susceptibility towards a progressive disease evolution, whereas the more controlled response of these cells in C57BL/6 mice possibly relates to the more resistant profile of this mouse strain.

NKT cells have been associated with protection against Leishmania donovani, yet their role in infections with Leishmania mexicana has not been addressed, nor has the activation pathway been defined after stimulation with Leishmania mexicana lipophosphoglycan (LPG). We analyzed the activation of NKT cells and their cytokine production in response to Leishmania mexicana LPG. Additionally we compared NKT-cell numbers and cytokine profile in lymph nodes of skin lesions induced by Leishmania mexicana in BALB/c and C57BL/6 mice. We show that LPG activates NKT cells primarily through the indirect pathway, initiating with TLR2 stimulation of dendritic cells (DC), thereby enhancing TLR2, MHC II, and CD86 expressions and IL-12p70 production. This leads to IFN-γ production by NKT cells. C57BL/6 mice showed enhanced DC activation, which correlated with augmented IFN-γ production by NKT cells. Additionally, infected C57BL/6 mice showed elevated percentages of NKT cells with higher IFN-γ and IL-4 production in lymph nodes. We conclude that the response of NKT cells towards Leishmania mexicana LPG initiates with the indirect activation, after binding of LPG to TLR2 in DC. This indirect activation pathway enables NKT cells to produce IFN-γ during the innate phase of Leishmania infection, the magnitude of which differs between mouse strains.

A new treatment regimen was tested on patients with incurable diffuse cutaneous leshmaniasis (DCL) infected with Leishmania mexicana mexicana in Mexico. Two patients with advanced stages of the disease were treated with polychemotherapy (pentamidine and allopurinol) combined with recombinant human interferon-gamma (rIFN-gamma). For determination of the best medication, parasites isolated from patient lesions were exposed to available drugs both as promastigotes and as intracellular amastigotes. A synergistic effect was observed in vitro for the combination of pentamidine and allopurinol. Both patients were treated and recovered rapidly, but one of them developed insulin-dependent type I diabetes because of pentamidine toxicity. The complication was controlled and both patients were discharged with an apparent parasitologic cure, but after 3 months the two patients began to relapse. Our results suggest that allopurinol-pentamidine polychemotherapy, involving reduced dosage of pentamidine, combined with rIFN-gamma is an alternative for DCL patients infected with L. m. mexicana.