Early Regulatory and Th2-Associated Responses Shape Resistance to Leishmania panamensis Infection in C57BL/6 Mice

Characterizing the specific interactions of Leishmania species with different host systems is essential for the development and validation of experimental infection models and for identifying potential therapeutic targets. Leishmania parasites elicit diverse host immune responses that result in different levels of disease severity. Here, we developed a murine model of L. panamensis infection and compared the responses of BALB/c and C57BL/6 mice following intradermal ear inoculation. BALB/c mice developed progressive ulcerative lesions associated with high parasite burden, whereas C57BL/6 mice exhibited a transient edema and maintained low parasite levels detected only at early stages of infection. C57BL/6 mice displayed early production of IL-13, IL-4, and IL-10, followed by delayed IFN-γ secretion. In contrast, BALB/c mice showed a mixed Th1/Th2 response at later stages of infection. Humoral responses also differed between strains, with BALB/c mice developing an early and sustained IgG1-dominated response, while C57BL/6 mice exhibited weak and delayed antibody production. These findings suggest that resistance to L. panamensis infection in C57BL/6 mice is associated with an early and transient Th2/regulatory response accompanied by a weak and delayed antibody production.