complement fixation

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

• noun The binding of active serum complement to an antigen-antibody pair. It is the basis for various diagnostic tests to detect the presence of a specific antigen or antibody.

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

• noun an immune response in which an antigen-antibody combination inactivates a complement (so it is unavailable to participate in a second antigen-antibody combination)