Platelet-mast cell dialogue in innate immune response and inflammation

Emerging evidence identifies platelets as active participants in inflammation beyond their traditional hemostatic function. Mast cells, tissue-resident granulocytes, are key players in innate immunity. Recent studies reveal dynamic bidirectional interaction between these two cell types. An IL33-driven feed-forward circuit has been described, in which mast cell-derived leukotriene C₄ activates platelets through cysteinyl leukotriene receptor 2 (CysLT₂R), whereas platelet-derived nucleotides subsequently enhance mast cell activation through P2Y1-dependent signaling. This reciprocal exchange redefines platelets and mast cells as cooperative amplifiers of type 2 inflammation rather than isolated effectors. The model challenges classical hierarchical views of immune signaling, proposing reciprocity where feedback strength, not stimulus persistence, determines inflammatory stability. Several mechanistic questions emerge, including the physiological magnitude of platelet-derived ATP/ADP flux in vivo, the spatial context of platelet-mast cell interactions within airway microenvironments, and whether other epithelial alarmins such as IL-25 and thymic stromal lymphopoietin (TSLP) engage similar pathways. Conceptually, this bilateral circuitry positions platelets as integral components of cytokine-driven networks that sustain allergic and asthmatic inflammation. Therapeutically, it suggests opportunities to target CysLT₂R and P2Y1 signaling to locally dampen inflammatory amplification without impairing systemic hemostasis. In addition, platelets contribute to vascular leakage, shock, and tissue inflammation following cardiac surgery through perivascular mast cell activation mediated by platelet-activating factors. Moreover, mast cell and platelet-derived 5-hydroxyindoleacetic acid signal through the GPR35 receptor to promote eosinophil recruitment and fungal persistence during Cryptococcus neoformans infection. Collectively, these findings broaden our understanding of platelet function and underscore the importance of intercellular communication in maintaining or disrupting the balance between transient and chronic inflammation.