anticomplement

[ăn′tē-kŏmplə-mənt, ăn′tī-]
n.
  1. A substance that neutralizes the action of a complement by combining with it and preventing its union with an antibody.
The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.