Rationale:
Acute respiratory distress syndrome is defined by the presence of systemic
hypoxia and consequent on disordered neutrophilic
inflammation. Local mechanisms limiting the duration and magnitude of this neutrophilic response remain poorly understood. Objectives: To test the hypothesis that during acute
lung inflammation tissue production of proresolution type 2
cytokines (IL-4 and IL-13) dampens the proinflammatory effects of
hypoxia through suppression of HIF-1α (hypoxia-inducible factor-1α)-mediated neutrophil adaptation, resulting in resolution of
lung injury. Methods: Neutrophil activation of IL4Ra (
IL-4 receptor α) signaling pathways was explored ex vivo in human
acute respiratory distress syndrome patient samples, in vitro after the culture of human peripheral blood neutrophils with recombinant
IL-4 under conditions of
hypoxia, and in vivo through the study of IL4Ra-deficient neutrophils in competitive chimera models and wild-type mice treated with
IL-4. Measurements and Main Results:
IL-4 was elevated in human BAL from patients with
acute respiratory distress syndrome, and its receptor was identified on patient blood neutrophils. Treatment of human neutrophils with
IL-4 suppressed HIF-1α-dependent hypoxic survival and limited proinflammatory transcriptional responses. Increased neutrophil apoptosis in
hypoxia, also observed with
IL-13, required active STAT signaling, and was dependent on expression of the
oxygen-sensing
prolyl hydroxylase PHD2. In vivo, IL-4Ra-deficient neutrophils had a survival advantage within a hypoxic inflamed niche; in contrast, inflamed lung treatment with
IL-4 accelerated resolution through increased neutrophil apoptosis. Conclusions: We describe an important interaction whereby IL4Rα-dependent type 2
cytokine signaling can directly inhibit hypoxic neutrophil survival in tissues and promote resolution of neutrophil-mediated
acute lung injury.