Transgenic Expression of CXCR3 on T Cells Enhances Susceptibility to Cutaneous Leishmania major Infection by Inhibiting Monocyte Maturation and Promoting a Th2 Response

Abstract

Cutaneous leishmaniasis, caused mainly byLeishmania major, an obligate intracellular parasite, is a disfiguring disease characterized by large skin lesions and is transmitted by a sand fly vector. We previously showed that the chemokine receptor CXCR3 plays a critical role in mediating resistance to cutaneous leishmaniasis caused byLeishmania major. Furthermore, T cells fromL. major-susceptible BALB/c but notL. major-resistant C57BL/6 mice fail to efficiently upregulate CXCR3 upon activation. We therefore examined whether transgenic expression of CXCR3 on T cells would enhance resistance toL. majorinfection in susceptible BALB/c mice. We generated BALB/c and C57BL/6 transgenic mice, which constitutively overexpressed CXCR3 under a CD2 promoter, and then examined the outcomes withL. majorinfection. Contrary to our hypothesis, transgenic expression of CXCR3 (CXCR3Tg) on T cells of BALB/c mice resulted in increased lesion sizes and parasite burdens compared to wild-type (WT) littermates afterL. majorinfection. Restimulated lymph node cells fromL. major-infected BALB/c-CXCR3Tgmice produced more interleukin-4 (IL-4) and IL-10 and less gamma interferon (IFN-γ). Cells in draining lymph nodes from BALB/c-CXCR3Tgmice showed enhanced Th2 and reduced Th1 cell accumulation associated with increased neutrophils and inflammatory monocytes. However, monocytes displayed an immature phenotype which correlated with increased parasite burdens. Interestingly, transgenic expression of CXCR3 on T cells did not impact the outcome ofL. majorinfection in C57BL/6 mice, which mounted a predominantly Th1 response and spontaneously resolved their infection similar to WT littermates. Our findings demonstrate that transgenic expression of CXCR3 on T cells increases susceptibility of BALB/c mice toL. major.