Susceptibility of inbred mice to Leishmania tropica infection: correlation of susceptibility with in vitro defective macrophage microbicidal activities.

Eleven mouse strains were inoculated in footpads with amastigotes of Leishmania tropica and observed for 12 weeks. Liver and spleen impression smears from infected mice were examined for the presence of intracellular parasites. Four strains (BALB/cJ, C57L/J, NZW/N, and P/J) failed to heal the subcutaneous lesion and showed evidence of systemic infection; the remaining seven strains (A/J, C3H/HeJ, C3H/HeN, C3HeB/FeJ, C57BL/6J, C57BL/10J, and C57BL/10ScN) were each resistant to infection and resolved their lesions by Week 10. Macrophages from the four susceptible strains could not be activated to kill L. tropica amastigotes by treatment with soluble lymphocyte products in vitro. In contrast, macrophages from all seven resistant strains responded to lymphokine treatment and eliminated 80-90% of intracellular parasites. These results suggest that in vitro macrophage microbicidal activities predict the course of systemic leishmanial disease.