gamma globulin

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

• noun A protein fraction of blood serum containing many antibodies that protect against bacterial and viral infectious diseases.
• noun A solution of gamma globulin prepared from human blood and administered for passive immunization against measles, German measles, hepatitis A, and other infections.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun A fraction of blood serum containing the most antibodies.
• noun A class of proteins in the blood, identified by their position after serum protein electrophoresis. The most significant gamma globulins are antibodies.

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

• noun a plasma protein containing the immunoglobulins that are responsible for immune responses