IL-4Rα Signaling in Keratinocytes and Early IL-4 Production Are Dispensable for Generating a Curative T Helper 1 Response in Leishmania major-Infected C57BL/6 Mice

Abstract

Experimental infection with the protozoan parasite Leishmania major has been extensively used to understand the mechanisms involved in T helper cell differentiation. Following infection, C57BL/6 mice develop a small self-healing cutaneous lesion and they are able to control parasite burden, a process linked to the development of T helper (Th) 1 cells. The local presence of IL-12 has been reported to be critical in driving Th1 cell differentiation. In addition, the early secretion of IL-4 was reported to potentially contribute to Th1 cell differentiation. Following infection with L. major, early keratinocyte-derived IL-4 was suggested to contribute to Th1 cell differentiation. To investigate a putative autocrine role of IL-4 signaling on keratinocytes at the site of infection, we generated C57BL/6 mice deficient for IL-4Rα expression selectively in keratinocytes. Upon infection with L. major, these mice could control their inflammatory lesion and parasite load correlating with the development of Th1 effector cells. These data demonstrate that IL-4 signaling on keratinocytes does not contribute to Th1 cell differentiation. To further investigate the source of IL-4 in the skin during the first days after L. major infection, we used C57BL/6 IL-4 reporter mice allowing the visualization of IL-4 mRNA expression and protein production. These mice were infected with L. major. During the first 3 days after infection, skin IL-4 mRNA expression was observed selectively in mast cells. However, no IL-4 protein production was detectable locally. In addition, early IL-4 blockade locally had no impact on subsequent Th1 cell differentiation and control of the disease. Taken together, the present data rule out a major role for skin IL-4 and keratinocyte IL-4Rα signaling in the development of a Th1 protective immune response following experimental infection with L. major.

Deletion of Interleukin-4 Receptor Alpha-Responsive Keratinocytes in BALB/c Mice Does Not Alter Susceptibility to Cutaneous Leishmaniasis

“…Previous studies have supported a role for IL-4 in driving a polarized Th1 response and conferring resistance to BALB/c mice during L. major infection ( 8 , 25 ). Conversely, during experimental cutaneous leishmaniasis in C57BL/6 mice with a global deletion of IL-4Rα, it was seen that the deletion had no impact on resistance in these mice ( 16 ). Dendritic cells are the primary source of IL-12 and initiate antigen-specific immunity to Leishmania ( 31 ).…”

“…As keratinocytes express surface IL-4 receptor, these cells are capable of both autocrine and paracrine stimulation ( 14 , 15 ). We recently demonstrated that C57BL/6 mice deficient for IL-4Rα-responsive keratinocytes were able to develop a protective Th1/type 1 effector response to L. major LV39 infection ( 16 ). However, considering that the impact of IL-4-mediated DC instruction was most pronounced in the susceptible BALB/c background in response to more virulent and less virulent strains of parasites, the role of early IL-4 signaling on keratinocytes needs to be investigated on a nonhealer BALB/c genetic background during cutaneous leishmaniasis to fully elucidate effector immune responses in response to infection with more virulent and less virulent L. major strains.…”

Mast cells as protectors of health

“…35 In addition to modulating DC maturation and granuloma formation, MC-derived IL-4 or TNF can contribute to this effect because these cytokines have been shown to directly promote T H 1 development. 100 In contrast, Paul et al 101 recently reported that MC-deficient mice independent of Kit mutations did not exhibit an altered progress of L major infection with regard to lesion sizes, parasite burden, or cytokine response compared with wild-type BALB/c or C57BL/6 mice, although effects on inflammatory cell recruitment were not studied. Information on the role of MCs in infected patients is not available.…”

Interleukin-4 Receptor Alpha: From Innate to Adaptive Immunity in Murine Models of Cutaneous Leishmaniasis

“…(B) Th1/Type 1-mediated protective immunity in C57BL/6 mice deficient for IL-4Rα-responsive keratinocytes. Similar to control C57BL/6 mice, KRT14 cre IL-4Rα −/lox C57BL/6 mice, generated by cre/ lox P targeting, controlled lesion development upon L. major LV39 and IL81 infection in the footpad or ear dermis, characterized by strong IFN-γ and IgG2c production and concomitantly reduced IL-4 and IgE ( 103 ). DC, dendritic cells; Mph, macrophage; LN, lymph node; Th1, T helper 1; Th2, T helper 2.…”

“…The use of both L. major LV39 and IL81 strains, injected subcutaneously in the footpad and ear, once again revealed unexpected results. In the absence of IL-4Rα-responsive keratinocytes, C57BL/6 mice controlled the development of inflammatory lesions upon infection with L. major LV39 and IL-81, which correlated with reduced parasite burdens and the expansion of Th1/type 1 cellular and humoral immune responses (Figure 5 B) ( 103 ). Collectively, the data obtained in both KRT14 cre IL-4Rα −/lox BALB/c and C57BL/6 mice mitigate an autocrine role for IL-4/IL-13 signaling on keratinocytes in the development of a non-healing Th2/type 2 or protective Th1/type 1 immune response, respectively, following experimental infection with L. major LV39 and IL-81 in mice.…”