Type 2 immune responses are defined by the cytokines interleukin 4 (IL-4), IL-5 and IL-13 and the cellular and physiological changes that these cytokines induce, including IgE production, eosinophilia, mast cell degranulation, mucus secretion and smooth muscle contraction. Together these responses provide a "weep and sweep" reflex that is optimised to expel parasitic worms. The same response can also be pathological when mis-timed or activated inappropriately. Current understanding of the orchestration and regulation of type 2 immunity is rapidly advancing, with recent identification of participating innate cells and elucidation of the cytokine signals responsible for their activation. In vivo, the outcome of cytokine signalling is critically dependent on timing, location and context. In this commentary, we describe the spatiotemporal control of type 2 cytokine signalling, consider its implications for bystander cells, and discuss its significance during co-infection.
Keywords: Bystander cells; Co-infection; Cytokine location; Cytokine signalling; IL-4.
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