immune reaction

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun The reaction resulting from the recognition and binding of an antigen by its specific antibody or by a previously sensitized lymphocyte.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun All the changes in a tissue that result from the action of a foreign substance introduced into an organism

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a bodily defense reaction that recognizes an invading substance (an antigen: such as a virus or fungus or bacteria or transplanted organ) and produces antibodies specific against that antigen