Encyclopedia of Health and Medicine

B
B-cell lymphocyte A type of white BLOOD cell
(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 RESPONSE upon detecting their presence,
and PLASMA cells, 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 LYMPH, 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 immediately
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.
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bronchus-associated lymphoid tissue (BALT)
Loosely organized clusters of LYMPH tissue beneath
the epithelium (tissue that forms the mucous lining)
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 BLOOD cells)
kill
• T-cell lymphocytes, which destroy PATHOGENbearing
cells
• B-cell lymphocytes, which produce the ANTI-
BODY IMMUNOGLOBULIN A (IgA), that helps keep
BACTERIA and 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-
GEN dispensation
BALT, like collections of accessory lymphoid tissue
elsewhere in the body, reinforces the presence
of the IMMUNE SYSTEM in areas where the body is
vulnerable to invasion of pathogens (viruses, bacteria,
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 INFLUENZA and PNEUMONIA.
For further discussion of BALT within the context
of the structures and functions of the immune
system, please see the overview section “The
Immune System and Allergies.”