The Foxp3 ⁺ regulatory T-cell population requires IL-4Rα signaling to control inflammation during helminth infections

Abstract

Forkhead box P3 (Foxp3 ⁺) regulatory T (Treg)-cell function is controlled by environmental cues of which cytokine-mediated signaling is a dominant component. In vivo, interleukin-4 (IL-4)-mediated signaling via IL-4 receptor alpha (IL-4Rα) mediates Treg cell transdifferentiation into ex-Foxp3 T helper 2 (Th2) or T helper 17 (Th17) cells. However, IL-4-mediated signaling also reinforces the Foxp3 Treg compartment in vitro. We generated Foxp3-specific IL-4Rα-deficient mice and demonstrated differential efficiency of IL-4Rα deletion in male (approximately 90%) and female (approximately 40%) animals, because of cyclic recombinase (Cre)-mediated X-linked foxp3 inactivation. Irrespective of the degree of IL-4Rα deletion within the Foxp3 ⁺ Treg cell population, mice showed exacerbation of immune effector responses with aggravated tissue pathology in tissue-dwelling helminth infections ( Schistosoma mansoni or Nippostrongylus brasiliensis). Mechanistically, IL-4Rα deletion in males and females led to a reduced expression of Foxp3 and subsequently an impaired accumulation of Foxp3 ⁺ Treg cells to inflamed tissues. In-depth cellular typing by flow cytometry revealed that the impairment of IL-4Rα-mediated signaling during helminth infections decreased the ability of central Treg cells to convert into effector Treg (eTreg) cells and caused a significant down-regulation of markers associated with Treg cell migration (C-X-C motif chemokine receptor 3 [CXCR3]) and accumulation in inflamed tissues (GATA binding protein 3 [GATA3]) as well as survival (B cell lymphoma 2 [Bcl-2]). These findings unprecedentedly, to our knowledge, uncover a role for IL-4Rα signaling in the positive regulation of Foxp3 ⁺ Treg cell function in vivo. Complementing our past knowledge on a widely reported role for IL-4Rα signaling in the negative regulation and transdifferentiation of Foxp3 ⁺ Treg cells in vivo, our present findings reveal the host requirement for an intact, but not reduced or potentiated, IL-4Rα-mediated signaling on Foxp3 ⁺ Treg cells to optimally control inflammation during helminth infections.

Author summary

Host soluble mediators such as cytokines play a key role in the regulation of the immune response. Forkhead box P3 (Foxp3 ⁺) regulatory T (Treg) cells, which are involved in maintaining self-tolerance and immune system homeostasis, are influenced by cytokines, including interleukin-4 (IL-4). However, opposing reports have emerged on the effect of this cytokine on Treg cells. Some evidence suggests IL-4 inhibits Treg cells, whereas other studies indicate a supportive role for this cytokine in Treg cell biology and function. To unambiguously address this question, we generated mice with IL-4 receptor specifically removed from the Treg cell population. Our newly generated mice did not show any sign of spontaneous inflammation during homeostasis, but when challenged with an experimental infection by parasitic worms, deletion of the IL-4 receptor from the Treg cell population led to increased inflammation and aggravated tissue pathology. Several defects such as poor activation, reduced promigratory marker expression, and reduced survival were apparent in Treg cells with impaired IL-4 responsiveness. Our evidence presents a strong case for a supportive role of IL-4 via IL-4 receptor in the biology and optimal regulatory function of Treg cells during worm infections.