Table 2.

Key immunologic definitions

Term	Definition
Affinity maturation	Process by which activated B cells can produce Igs with increased affinity; it is a direct result of somatic hypermutation
Somatic hypermutation	Cellular mechanism involving a programmed process of mutation affecting the variable regions of Ig genes
Activation-induced cytidine deaminase	Enzyme that creates DNA mutations during somatic hypermutation and affinity maturation
CD89	Also called FcαRI; is the human receptor binding the IgA heavy chain constant region
Chimeric IgA	IgA composed of domains from distinct species (e.g., mouse and human)
Germline sequence	Inherited sequence before undergoing somatic mutation