IL4 and infection: Once this process takes place, MCs undergo degranulation to release mediators such as histamine, IL-4 and IL-13 that are involved in activating alternative macrophages (M2), TNF-α, CXCL1, and CXCL2, resulting in neutrophil accumulation at the site of infection, and prostaglandin D2 causing IL-33 cleavage, which in turn increases the induction of Type 2 innate lymphoid cells via the CRTH2 receptor.