1. Antibody is a protein produced by the body's immune system in response to a foreign substance (antigen).

Notes: An antibody reacts specifically with the antigen that induced its formation and inactivates the antigen. The human bodies fight off an infection by producing antibodies.

2. A protein produced by the body’s immune system in response to a foreign substance (antigen). Our bodies fight off an infection by producing antibodies. An antibody reacts specifically with the antigen that triggered its formation and its function is to inactivate the antigen.