B

B-cell lymphocyte A type of white BLOODcell
(LEUKOCYTE) responsible for ANTIBODY-MEDIATED
IMMUNITY(also called humoral immunity). B-cell
lymphocytes are so named because they come to
maturity in the BONE MARROW(in contrast to T-cell
lymphocytes, which come to maturity in the THY-
MUS). B-cell lymphocytes produce antibodies in
reaction to the presence of antigens. The bone
marrow generates millions of B-cell lymphocytes
each day. Each B-cell lymphocyte is specific for a
unique ANTIGEN.
B-cell lymphocytes may be memory B-cells,
which “remember” specific antigens to mobilize a
rapid IMMUNE RESPONSEupon detecting their pres-
ence, and PLASMAcells, which produce antibodies.

• Plasma cells generate antibodies in response to
  the presence of antigens.


• Memory B-cells remain in the circulation of the
  blood and LY M P H, carrying inactive antibodies.
  Each memory B-cell has antibodies specific to a
  particular antigen the immune response has
  previously encountered. When the memory B-
  cell encounters the antigen again, it immedi-
  ately begins producing antibodies.

Health conditions that affect B-cell lymphocytes
include cancers, such as certain types of LEUKEMIA
and lymphoma, and acquired immune and
AUTOIMMUNE DISORDERS.
For further discussion of B-cell lymphocytes
within the context of the structures and functions
of the immune system, please see the overview
section “The Immune System and Allergies.”
See also CELL-MEDIATED IMMUNITY; HIV/AIDS; T-CELL
LYMPHOCYTE.

biological response modifier See IMMUNOTHERAPY.

bronchus-associated lymphoid tissue (BALT)

Loosely organized clusters of LY M P Htissue beneath

the epithelium (tissue that forms the mucous lin-

ing) of the bronchi (inner airways) in the LUNGS.

These clusters of lymph tissue have preventive,

protective, and cleanup responsibilities within the

IMMUNE RESPONSE. They contain

• macrophages and dendritic cells, which are
  phagocytic cells that consume the debris of
  pathogens other leukocytes (white BLOODcells)
  kill


• T-cell lymphocytes, which destroy PATHOGEN-
  bearing cells


• B-cell lymphocytes, which produce the ANTI-
  BODY IMMUNOGLOBULINA (IgA), that helps keep
  BACTERIAand viruses from adhering to mucous
  tissues, such as the lining of the nasal sinuses
  and the bronchi


• M cells (folded, M-shaped cells that engulf
  pathogens and transport them to phagocytes),
  which participate in the various stages of ANTI-
  GENdispensation

BALT, like collections of accessory lymphoid tis-

sue elsewhere in the body, reinforces the presence

of theIMMUNE SYSTEMin areas where the body is

vulnerable to invasion of pathogens (viruses, bac-

teria, and other potentially harmful substances). A

specific role of BALT is to provide an extra layer of

immune protection to block or limit access by

viruses that cause infections specific to the lungs,

such as INFLUENZAand PNEUMONIA.

For further discussion of BALT within the con-

text of the structures and functions of the immune

system, please see the overview section “The

Immune System and Allergies.”

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