Anaphylaxis refers to

The general mechanism of immediate hypersensitivity involves a series of steps. An antigen induces the formation of IgE antibody, which binds firmly by its Fc poion to high-affinity IgE receptors on mast cells, basophils, and possibly eosinophils.Sometime later, an individual experiences a second exposure to the same antigen. This second exposure results in the cross-linking of the cell-bound IgE molecules and the release of pharmacologically active mediators.Jawetz 27e pg: 145