Antibodies.

Antibodies are proteins produced by the B lymphocyte white blood cells of the immune system of human and nonhuman animals in response to the introduction of foreign material such as viruses, bacteria, or parasites and their molecules. A particular B lymphocyte, or B cell, and its progeny cells (clones) produce a singular antibody molecule that binds specifically to a structural determinant on a specific foreign molecule (antigen). A given antigen may elicit different antibodies from a number of genetically distinct B lymphocytes, each of which produces a single type of antibody that binds to a select part of the foreign molecule. Such diverse antibody production is called polyclonal response, and the products are called polyclonal antibodies.