isoprecipitin

[ī′sō-prĭ-sĭpĭ-tĭn]
n.
  1. An antibody that combines with and precipitates soluble antigenic material in the plasma or serum of another member, but not all members, of the same species.
The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.