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

Abstract

e Cutaneous leishmaniasis, caused mainly by Leishmania 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 by Leishmania major. Furthermore, T cells from L. major-susceptible BALB/c but not L. 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 to L. major infection 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 with L. major infection. Contrary to our hypothesis, transgenic expression of CXCR3 ( Leishmaniasis affects over 12 million people worldwide and, according to recent estimates, almost 2 million people are affected annually (1). It is therefore a major global health problem and has been classified by the World Health Organization as a neglected tropical disease. The most common form of the disease is cutaneous leishmaniasis (CL), which is caused by Leishmania major, Leishmania tropica, or Leishmania aethiopica in the Old World and by Leishmania mexicana species complex or Leishmania (Viannia) braziliensis species complex in the New World. CL is characterized by the development of large papular or nodular lesions at the infection site, which often become ulcerated and may persist for months or even years. In some patients, lesions can become chronic, leading to disfiguring mucosal leishmaniasis. There are currently no vaccines available for the disease, and resistance to first-line drugs is becoming increasingly common (2, 3).In murine models of CL, it is well established that protective host immunity depends on the generation and recruitment of appropriate Th1 immune cells to the site of infection. The hallmark of Th1 responses is the production of gamma interferon (IFN-␥), which activates mononuclear phagocytes, increases the production of reactive nitrogen species (RNS), and enhances parasite killing (4, 5). CXCR3 is a chemokine receptor which is preferentially expressed on Th1 cells and activated CD8 ϩ T cells and coordinates their recruitment to inflammatory sites where they exert their effector function. CXCR3 is regulated by the transcription factor T-bet, a master regulator of Th1 responses. CXCR3 has been shown to be important in immunity to intracellular parasites which require a Th1 immune response for protection, including L. major. Genetic deletion of cxcr3 in C57BL/6 (BL/6) mice, which are naturally resistant to L. major, renders them susceptible to localized infection. Although these mice are able to generate a Th1 immune response in the draining lymph nodes, they are unable to control parasite growth in the lesion due to defective CD4 ϩ and CD8 ϩ T cell migration to the site of infection (6). More recent studies have s...

Transgenic T cell-specific expression of CXCR3 enhances splenic and hepatic T cell accumulation but does not affect the outcome of visceral leishmaniasis

“…These results indicated that CXCR3 is important for trafficking of activated T cells into infection sites for the generation of leishmanicidal immune response. Surprisingly when CXCR3 Tg mice were infected with L. major , these mice developed larger lesions characterized by a Th2 skewed immune response [11]. In addition to highlighting the complex role for CXCR3 in progression of leishmaniasis, these studies suggest that resistance is dependent on which T cell subsets undergo CXCR3-mediated activation and home into the lymph nodes and sites of infection.…”

“…CXCR3 transgenic mice (CXCR3 Tg ) were generated by the procedure described previously [11]. C57BL/6 CXCR3 Tg were backcrossed to WT BALB/c mice for 10 generations to generate BALB/c CXCR3 Tg mice and BALB/c wild-type littermates (CXCR3 +/+ ).…”

“…Flow cytometry was performed on single cell suspensions prepared from spleens of CXCR3 Tg and CXCR3 +/+ mice as described previously [11]. Briefly, cells were blocked with normal mouse serum and incubated with conjugated antibodies against various cell surface markers including CD3, CD4, CD8, CXCR3 and CD69 (Biolegend).…”

“…Absorbance values were used to calculate the rate of alamarBlue reduction and thereby, T cell proliferation using online alamarBlue colorimetric calculator (AbD Serotec). At 72 h, culture supernatants were also collected to determine concentrations of cytokines such as IFN-γ, IL-4, IL-6, IL-10, and IL-13 using anti-mouse capture and detection antibodies (Biolegend) [11]. Recombinant mouse cytokines (BD Biosciences) were used as standards.…”

The IL-33/ST2 Axis in Immune Responses Against Parasitic Disease: Potential Therapeutic Applications

“…The most common form is cutaneous leishmaniasis (CL), which causes painless localized skin lesions leading to severe tissue damage and disfigurement without treatment (Varikuti et al, 2017). CL is caused by L. major, L. tropica and L. aethiopica in the old world (Asia and Africa) and L. mexicana and L. braziliensis in the New World (Central and South America) (Oghumu et al, 2015). The most severe form of the disease is Visceral Leishmaniasis (VL) which is mainly caused by L. donovani, L. chagasi and L. infantum (McGwire and Satoskar, 2014).…”