plasma cell

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

• noun Any of the antibody-secreting cells found in lymphoid tissue and derived from B cells upon lymphokine stimulation and reaction with a specific antigen.

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

• noun a form of lymphocyte that produces antibodies when reacted with a specific antigen; a plasmacyte

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

• noun a cell that develops from a B lymphocyte in reaction to a specific antigen; found in bone marrow and sometimes in the blood