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Leishmaniasis is a neglected tropical disease with diverse infection outcomes ranging from self-healing lesions, to progressive non-healing lesion, to metastatic spread and destruction of mucous membranes. Although resolution of cutaneous leishmaniasis is a classic example of type-1 immunity leading to well controlled self-healing lesions, an excess of type-1 related inflammation can contribute to immunopathology and metastatic spread of disease.Leishmaniagenetic diversity can contribute to variation in polarization and robustness of the immune response through differences in both pathogen sensing by the host and immune evasion by the parasite. In this study, we observed a difference in parasite chemokine suppression between theLeishmania (L.)subgenus and theViannia (V.)subgenus, which is associated with severe immune mediated pathology such as mucocutaneous leishmaniasis. WhileLeishmania (L.)subgenus parasites utilize the virulence factor and metalloprotease glycoprotein-63(gp63)to suppress the type-1 associated host chemokine CXCL10,L. (V.) panamensisdid not suppress CXCL10. To understand the molecular basis for the inter-species variation in chemokine suppression, we usedin silicomodeling of the primary amino acid sequence and protein crystal structures to identify a putative CXCL10-binding site on GP63. We found the putative CXCL10 binding site to be located in a region ofgp63under significant positive selection and that it varies from theL. majorwild-type sequence in allgp63alleles identified in theL. (V.) panamensisreference genome. We determined that the predicted binding site and adjacent positively selected amino acids are required for CXCL10 suppression by mutating wild-typeL. (L.) major gp63to theL. (V.) panamensisallele and demonstrating impaired cleavage of CXCL10 but not a non-specific protease substrate. Notably,Vianniaclinical isolates confirmed thatL. (V.) panemensisprimarily encodes non-CXCL10-cleavinggp63alleles. In contrast,L. (V.) braziliensishas an intermediate level of activity, consistent with this species having more equal proportions of both alleles at the CXCL10 binding site, possibly due to balancing selection. Our results demonstrate how parasite genetic diversity can contribute to variation in the host immune response toLeishmaniaspp. infection that may play critical roles in the outcome of infection. |
