A type II immunologic reaction is an antibody-antigen reaction. A good example is Rh incompatibility. These reactions are not IgE-mediated; they are mediated by IgG binding to a protein. In Rh incompatibility, the maternal IgG binds to the Rh protein on the infant's red blood cells. IgG reactions do not cause the symptoms seen in the child described in the vignette.

A type III immunologic reaction involves binding of IgG antibodies to an antigen, which triggers the complement cascade. An example of this type of reaction is serum sickness. Symptoms of this type of reaction are fever, joint pain, and swollen glands.

A type IV immunologic reaction is best exemplified by tuberculosis purified protein derivative test. This delayed type hypersensitivity reaction is mediated by T cells, not antibodies, and usually occurs 48 to 72 hours after the exposure. It is not characterized by rash, emesis, and irritability.

The child in the vignette is experiencing an IgE-mediated type I reaction to milk antigen in which IgE attaches to mast cells that bind with the milk antigen. Subsequent degranulation of the mast cells causes the symptoms described.