B cell

Also from Answers.com... Herpes What is Herpes? Learn the signs and symptoms.

Any of the lymphocytes that mature in the bone marrow and, when stimulated by a particular antigen, differentiate into plasma cells. Also called B lymphocyte.

[b(ursa-dependent) cell, after the bursa of Fabricius, a gland in birds where the cells mature and the first such tissue found in vertebrates.]

1. See beta cell.
2. A type of lymphocyte that, when stimulated by a particular antigen, differentiates into plasma cells that synthesize the antibodies that circulate in the blood and react with the specific antigens. Also called B lymphocyte.

The noun has one meaning:

Meaning #1: a lymphocyte derived from bone marrow that provides humoral immunity; it recognizes free antigen molecules in solution and matures into plasma cells that secrete immunoglobulin (antibodies) that inactivate the antigens
  Synonym: B lymphocyte