Encyclopedia of Health and Medicine

254 The Immune System and Allergies
new BLOOD vessels) 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 angiogenesis,
which has the potential to starve tumors.
See also IMMUNOTHERAPY; LEUKOCYTE; LYMPHOCYTE;
MACROPHAGE; TUMOR NECROSIS FACTORS (TNFS).
clusters of differentiation A system of classifying
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 normal
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 ANTIGEN presentation
• 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 IMMUNOGLOBULIN M (IgM)
• CD-7, which populates T-cell lymphocytes in
acute lymphocytic LEUKEMIA (ALL) and is a
marker for STEM CELL leukemias
• CD-8, which populates T-suppressor cells (T-cell
lymphocytes that end the immune response)
and is a key marker for monitoring the progression
of HIV/AIDS
CD-4 AND HIV/AIDS
CD-4 has become an important marker in tracking
the progression of HIV/AIDS, as HIV-1 and
HIV-2 bind with this ANTIGEN to gain access to
the body. CD-4 receptors are abundant on certain
T-cell lymphocytes called T-helper cells (also
called T 4 cells). In health, CD-4 coordinates
numerous aspects of the IMMUNE RESPONSE. When
pathogens such as HIV bond with CD-4 receptors,
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 INFECTION that 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
BLOOD cells) in the BONE MARROW. The body produces
minute quantities of CSFs to regulate LEUKO-
CYTE production, 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 IMMUNOABLATION during the course of treatment
for some forms of LEUKEMIA and certain other
cancers for which BONE MARROW TRANSPLANTATION is
a treatment option, and some chemotherapeutic
regimens that are known to be very ablative to the
white blood cells. Immunoablation uses high-DOSE
CHEMOTHERAPY or RADIATION THERAPY to destroy the
diseased bone marrow. During the approximately
six weeks it takes for the transplanted bone marrow
to begin producing new blood cells, the person
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.