Mast cells augment lesion size and persistence during Experimental Leishmania major infection in the mouse

Mast cells are a source of a variety of cytokines that may influence the host response to Leishmania major. To investigate the role of mast cells during L. major infection, we performed a morphometric analysis of mast cells at cutaneous sites in resistant C57BL/6 mice and susceptible BALB/c mice injected with L. major. Extensive dermal mast cell degranulation was found at sites of L. major infection in both strains of mice. We also examined the course of L. major infection in genetically mast cell-deficient WBB6F₁- W/W(v) or WCB6F₁-SI/SI(d) mice, their respective congenic normal (WBB6F₁- +/+ or WCB6F₁-+/+) littermates, and WBB6F₁-W/W(v) mice that had been selectively and locally repaired of their cutaneous mast cell deficiency. We found that mast cells significantly augmented the intensity and maximal size of the cutaneous lesions at sites of L. major infection, and in some cases substantially prolonged the persistence of the reactions. However, the lesions ultimately resolved in both the mast cell-deficient and the congenic normal mice. In addition, the presence or absence of mast cells had little or no effect on the numbers of viable parasites recovered from the cutaneous lesions. Moreover, mast cell-deficient W/W(v) mice and the congenic normal (+/+) mice produced similar levels of IFN-γ mRNA in lymph nodes draining the cutaneous lesions whereas no IL-4 mRNA was detectable. Taken together, these data suggest that mast cells significantly augment the size of cutaneous lesions during L. major infection in mice. However, mast cells do not appear to influence significantly either the parasite burden or the ultimate resolution of the infection.