Figure 3. Eosinophil - mast cell interactions.

Schematic representation of interactions between eosinophils and mast cells. Eosinophils release pre-formed mediators including stem cell factor (SCF), nerve growth factor (NGF), and leukotrienes C₄ and E₄ (LTC₄/E₄); these mediators elicit a functional response through activation of specific receptors on mast cells, including c-KIT receptor (CD117), tropomyosin-receptor kinase A (Trak A), and leukotriene receptors (LTC₄R and LTE₄R). Mast cell degranulation promoted by allergens via cross-linking of high-affinity immunoglobulin E receptors (FcεRI) results in release of histamine that can acts on eosinophils through the histamine receptor 4 (HR₄). Activated mast cells also regulate eosinophil function via the activation of cytokine receptors, leukotriene receptors (LTB₄R and LTC₄R), prostaglandin D₂ (PGD₂) receptor (CRTH2), chemokine receptors (CXCRs) and other G-protein coupled receptors (GPCRs). Mast cells and eosinophils also maintain inhibitory immunoreceptor tyrosine-based inhibition motif (ITIM)-bearing receptors (IRs) and Siglecs, both of which serve to downregulate immune responses (128).