Von Pirquet (1906) coined the term "allergy" to describe the state of
altered reactivity that occurs after exposure of a human being or animal
to an antigenic stimulus. This altered reactivity can manifest itself as either
a hypersensitivity to antigen (whereby the allergic response leads to tissue
distruction) or a hyposensitivity such as specific tolerance (reviewed by
Habicht et al., 1973) or cell mediated suppression (reviewed by Gershon,
1974; Asherson and Zembala, 1975).