coagglutinin

[kō′ə-glōōtn-ĭn]
n.
  1. A substance that does not agglutinate an antigen, but induces the agglutination of an antigen that is appropriately coated with a univalent antibody.
The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.