Platelet-macrophage cooperation drives IL-33-dependent type 2 lung immunopathology in a sex-biased manner

Background: Platelets amplify lung type 2 inflammation (T2I), but the underlying mechanisms remain incompletely understood. Objective: To elucidate the platelet-driven T2I mechanisms, particularly the role of platelet-derived leukotriene C4 (LTC4). Methods: We assessed lung T2I to Alternaria alternata extract (Alt) in vivo using mice with targeted deletions of Ltc4s in platelets, macrophages, or mast cells; Il33 in macrophages, hematopoietic cells, or alveolar type 2 (AT2) cells; and cysteinyl leukotriene receptors. Exogenous administration of LTC4 and IL-33 in naïve mice complemented the genetic models. Sex- and age-matched mice were randomly assigned, and histopathological evaluations were performed under blinded conditions. Results: Platelets promoted IL-33 expression in perivascular macrophages and induced transcellular LTC4 synthesis. Although platelet Ltc4s was not needed to induce IL-33+macrophages, it promoted both IL-33+AT2 cell and group 2 innate lymphoid cell (ILC2) expansions in a sex-biased manner. Platelet depletion abrogated Alt-induced increases in IL-33 and AT2 cell expansion. Platelet-adherent macrophages expressed higher IL-33 than non-adherent counterparts. Platelet-specific Ltc4s deletion reduced eosinophil, ILC2, and AT2 cell expansion in females in a delayed manner. Macrophage-specific Il33 deletion eliminated platelet-driven IL-33 increases and attenuated AT2 cell expansion selectively in females. Exogenous LTC4 and IL-33 synergistically induced IL-33+macrophages and expanded AT2 cells. Conclusion: Adherent platelets rapidly upregulate IL-33 expressing macrophages, and platelet-derived LTC4 sustains IL-33-driven expansion of AT2 cells and ILC2s, driving sex-biased amplification of T2I. This platelet-macrophage axis may contribute to sex differences in type 2 inflammatory airway diseases such as asthma.