If the following features of the atopic reaction were placed in their correct order which would come fourth?

The answer is A. Atopy (anaphylactic, immediate or type 1 hypersensitivity) occurs when IgE binds to mast cells and causes degranulation; antigen is absorbed (C) and the immune response produces specific IgE (E) which binds by its Fc component to mast cells (D); subsequent exposure to the antigen (A) results in antigen trapping by the IgE Fab components on the mast cells with subsequent degranulation (B).