Deletion of IL-4 Receptor Alpha on Dendritic Cells Renders BALB/c Mice Hypersusceptible to Leishmania major Infection

Abstract

In BALB/c mice, susceptibility to infection with the intracellular parasite Leishmania major is driven largely by the development of T helper 2 (Th2) responses and the production of interleukin (IL)-4 and IL-13, which share a common receptor subunit, the IL-4 receptor alpha chain (IL-4Rα). While IL-4 is the main inducer of Th2 responses, paradoxically, it has been shown that exogenously administered IL-4 can promote dendritic cell (DC) IL-12 production and enhance Th1 development if given early during infection. To further investigate the relevance of biological quantities of IL-4 acting on DCs during in vivo infection, DC specific IL-4Rα deficient (CD11ccreIL-4Rα-/lox) BALB/c mice were generated by gene targeting and site-specific recombination using the cre/loxP system under control of the cd11c locus. DNA, protein, and functional characterization showed abrogated IL-4Rα expression on dendritic cells and alveolar macrophages in CD11ccreIL-4Rα-/lox mice. Following infection with L. major, CD11ccreIL-4Rα-/lox mice became hypersusceptible to disease, presenting earlier and increased footpad swelling, necrosis and parasite burdens, upregulated Th2 cytokine responses and increased type 2 antibody production as well as impaired classical activation of macrophages. Hypersusceptibility in CD11ccreIL-4Rα-/lox mice was accompanied by a striking increase in parasite burdens in peripheral organs such as the spleen, liver, and even the brain. DCs showed increased parasite loads in CD11ccreIL-4Rα-/lox mice and reduced iNOS production. IL-4Rα-deficient DCs produced reduced IL-12 but increased IL-10 due to impaired DC instruction, with increased mRNA expression of IL-23p19 and activin A, cytokines previously implicated in promoting Th2 responses. Together, these data demonstrate that abrogation of IL-4Rα signaling on DCs is severely detrimental to the host, leading to rapid disease progression, and increased survival of parasites in infected DCs due to reduced killing effector functions.

IL-4–producing B cells regulate T helper cell dichotomy in type 1- and type 2-controlled diseases

“…As expected, global IL-4Rα −/− knockout mice controlled both LV39 and IL81 infection in the footpad in the acute phase (Fig. S1C) in line with previous reports (21,25). Challenging with soluble L. major antigen (SLA) in 6 wk-infected mb1 cre IL-4Rα -/lox BALB/c mice resulted in increased delayed-type hypersensitivity (DTH) (Fig.…”

“…As expected following L. major infection ( Fig. 1 A and B), littermate IL-4Rα -/lox BALB/c mice developed rapidly growing necrotic lesions (N12/14), leading to fulminant cutaneous leishmaniasis within 8 wk of infection, similar to WT BALB/c (IL-4Rα +/+ mice) (21,25,26), whereas the healer C57BL/6 strain controlled tissue pathology without development of necrosis (N0/14) and ulceration (19,21,25,26 …”

“…Another source of early IL-4 after L. major infection is attributed to the CD4 + T cells expressing the Vβ4Vα8 T cell receptor that recognizes the Leishmania antigen LACK (Leishmania homolog of receptors for activated C kinase) (36). Importantly, progressive infection in susceptible strains is attributed to sustained IL-4 production and an inability to redirect this early Th2 response toward a protective Th1 response (18,20,25). Collectively, B cells could become activated by directly responding to antigen, releasing this early IL-4, and in an autocrine loop, enhancing the…”

“…These discrepancies have been attributed to strain differences in the source of parasites, parasite dose, and the embryonic stem cells used to generate IL-4 knockout mice. Moreover, apart from a Th2-promoting role, IL-4 has also been reported to instruct DCs to secrete IL-12 for protective Th1 responses to L. major LV39 (25,52) and shown to instruct protective immunity and successful chemotherapy to L. donovani infection (53). Altogether, these reports and the work presented here highlight that IL-4 plays a dynamic, multifaceted role in the spectrum of human leishmaniasis, and these differing roles must be considered in targeting this cytokine in a treatment or vaccine.…”

“…We observed that parasite replication in the footpad of B-IL-4 −/− and IL-4 −/− chimeras was controlled to a greater degree than in the LN compared with μMT B-WT chimeras. The footpad has a higher frequency of iNOS-secreting macrophages and DCs to host parasites than the LN and is capable of killing intracellular parasites (25,27), which might account for a slower but effective control in the LN. This was further accompanied by strikingly reduced detrimental type 2 antibody (Fig.…”