new BLOODvessels) that occurs when both HEALING
and tumor progression (such as in cancer) takes
place. Researchers are exploring ways to target
chemokines as a means of shutting down angio-
genesis, which has the potential to starve tumors.
See also IMMUNOTHERAPY; LEUKOCYTE; LYMPHOCYTE;
MACROPHAGE; TUMOR NECROSIS FACTORS(TNFS).
clusters of differentiation A system of classify-
ing lymphocytes according to the collections of
antigens on the surface of their cell membranes,
also called CD markers. Each CD has a specific role
in cell signaling and communication, guiding cell
function and response. CDs are critical to the nor-
mal function of the IMMUNE SYSTEM. Some of the
major CDs are
- CD-1, which populates B-cell lymphocytes and
macrophages and has a role in ANTIGENpresen-
tation - CD-2, which populates T-cell lymphocytes and
natural killer (NK) cells and activates T-cells - CD-3, which populates T-cell lymphocytes and
facilitates antigen binding (the ability of T-cell
lymphocytes to receive biochemical messages) - CD-4, which populates T-helper cells (T-cell
lymphocytes that direct IMMUNE RESPONSE to
INFECTION) and is a key marker for monitoring
the progression of HIV/AIDS - CD-5, which populates B-cell lymphocytes that
produce IMMUNOGLOBULINM (IgM) - CD-7, which populates T-cell lymphocytes in
acute lymphocytic LEUKEMIA (ALL) and is a
marker for STEM CELLleukemias - CD-8, which populates T-suppressor cells (T-cell
lymphocytes that end the immune response)
and is a key marker for monitoring the progres-
sion of HIV/AIDS
CD-4 AND HIV/AIDS
CD-4 has become an important marker in track-
ing the progression of HIV/AIDS, as HIV-1 and
HIV-2 bind with this ANTIGENto gain access to
the body. CD-4 receptors are abundant on cer-
tain T-cell lymphocytes called T-helper cells (also
called T 4 cells). In health, CD-4 coordinates
numerous aspects of the IMMUNE RESPONSE. Whenpathogens such as HIV bond with CD-4 recep-
tors, they block the ability of CD-4 to signal
other immune cells. This communication failure
disrupts the IMMUNE SYSTEM’s ability to mount an
effective immune response. HIV also uses the T-
helper cells to replicate itself, further spreading
INFECTION. In combination, these events allow
OPPORTUNISTIC INFECTIONthat can overwhelm the
body.See also ANTIBODY; CYTOKINES; HUMAN LEUKOCYTE
ANTIGENS (HLAS); B-CELL LYMPHOCYTE; LYMPHOCYTE;
MACROPHAGE; MAJOR HISTOCOMPATABILITY COMPLEX
(MHC); MONOCLONAL ANTIBODIES (MABS); NATURAL
KILLER(NK) CELL; PHENOTYPE; T-CELL LYMPHOCYTE.colony-stimulating factors (CSFs) Molecules
that stimulate the growth of leukocytes (white
BLOODcells) in the BONE MARROW. The body pro-
duces minute quantities of CSFs to regulate LEUKO-
CYTEproduction, maintaining the various types of
leukocytes at appropriate levels to meet the needs
of immune function. CSF production increases
during INFECTION and other demands for higher
quantities of white blood cells.
In the 1990s researchers isolated the genes that
encode CSFs, permitting the use of recombinant
technology to create synthetic versions of CSFs for
therapeutic applications. Today doctors administer
CSFs to rapidly restore white blood cell production
after IMMUNOABLATIONduring the course of treat-
ment for some forms of LEUKEMIAand certain other
cancers for which BONE MARROW TRANSPLANTATIONis
a treatment option, and some chemotherapeutic
regimens that are known to be very ablative to the
white blood cells. Immunoablation uses high-DOSE
CHEMOTHERAPYor RADIATION THERAPYto destroy the
diseased bone marrow. During the approximately
six weeks it takes for the transplanted bone mar-
row to begin producing new blood cells, the per-
son has no immune function and is extremely
vulnerable to infection. CSF therapy dramatically
shortens this period of vulnerability, stimulating
leukocyte production within days of the bone
marrow transplantation.
See also CYTOKINES; GENE; HEMATOPOIESIS; IMMUNE
RESPONSE; IMMUNOSUPPRESSIVE THERAPY; RECOMBINANT
DNA.254 The Immune System and Allergies