Definition of "opsonin" [opsonin]

• An antibody or product of complement activation in blood serum that causes bacteria or other foreign cells to become more susceptible to the action of phagocytes. (noun)

American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.

• "I call opsonin, goes on in the system by ups and downs -- Nature being always rhythmical, you know -- and that what the inoculation does is to stimulate the ups or downs, as the case may be."
• "The "opsonin," or "relish," is something exuded into or produced in the blood fluid when the attacking microbe arrives."
• "In the absence of the relish (the Greek word for it used by Sir Almroth Wright, its discoverer, is "opsonin"), the eater-cells are sluggish -- too sluggish -- in their work."