<prompt> The most important cells in type I hypersensitivity:MacrophagesMast cellsNeutrophilsLymphocytes  <response>: Ans. is b i.e., Mast cellsRef: Ananthanarayan, 9the, p. 162; Robbins 7the, p. 206 Priming Ag - Antigen presenting cell - T cell - Th 2 - B cell - IgE - Mast cell coated with IgE Fc. Shocking dose - IgE Fab binds to Ag - Mast cell degranulation. Primary mediator Histamine, Serotonin, chemotactic factor and secondary factor PG and cytokines - Typical manifestations like Anaphylaxis etc. 