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superinfection immunity 671 suppressor T cell factor (TSF)
Antigen presenting
cell
on the MHC protein outside the peptide-binding groove and
with the CDR2 of selected TCRβ chains. Selected bacterial
toxins may stimulate all T lymphocytes that contain a certain
family of Vβ T cell receptor (TCR) genes. Superantigens
may induce proliferation of 10% of CD4 + T cells by combining
with the TCR Vβ and the MHC HLA-DR α-1 domain.
Superantigens are thymus-dependent (TD) antigens that do
not require phagocytic processing. Instead of fitting into
the TCR internal groove where a typical processed peptide
antigen fits, superantigens bind to the external regions of αβ
TCRs and simultaneously link to DP, DQ, or DR molecules
on antigen-presenting cells. Superantigens react with multiple
TCR molecules with similar peripheral structures. Thus,
they stimulate multiple T cells that augment protective T
and B cell antibody responses. This enhanced responsiveness
to antigens such as toxins produced by staphylococci
and streptococci is an important protective mechanism in an
infected individual. Several staphylococcal enterotoxins are
superantigens and may activate many T cells, resulting in the
release of large quantities of cytokines to produce a clinical
syndrome resembling septic shock.
superinfection immunity
The inability of two related organisms (for example, plasmids)
to invade a host cell at the same time.
superoxide anion
A free radical formed by the addition of an electron to an
oxygen molecule, causing it to become highly reactive. This
process takes place in inflammation or is induced by ionizing
radiation. The anion is formed by reduction of molecular
oxygen in polymorphonuclear neutrophils (PMNs) and
mononuclear phagocytes. The hexose monophosphate shunt
activation pathway enhances superoxide anion generation.
Superoxide anion interacts with protons, additional
superoxide anions, and hydrogen peroxide. Oxidation of one
superoxide anion and reduction of another may lead to the
formation of oxygen and hydrogen peroxide. Superoxide dismutase
found in phagocytes catalyzes this reaction. Injury
induced by superoxide anion is associated with age-related
degeneration. It may also serve as a mutagen with implications
for carcinogenesis. It plays a pivotal role in the ability
of mononuclear phagocytes and neutrophils to kill microorganisms
through their oxidative microbicidal functions.
ICAM-1
MHC
LFA-3
α helices
CD4 or CD8
LFA-1
CD2 TCR
Antigen peptide
Superantigen
T Cell
Cellular and molecular interactions in antigen presentation.
superoxide dismutase
An enzyme that defends an organism against oxygen-free
radicals by catalyzing the interactions of superoxide anions
with hydrogen ions to yield hydrogen peroxide and oxygen.
suppressin
A 63-kDa, single polypeptide chain molecule with multiple
disulfide linkages and a phagocytic index (PI) of 8.1. It is
produced by the pituitary and lymphocytes and is a negative
regulator of cell growth. It inhibits lymphocyte proliferation
and is more effective on T cells than on B cells.
Suppressin has properties similar to transforming growth
factor β (TGF-β), although it is structurally different.
Antisuppressin antibody leads to T or B cell proliferation.
suppression
Immunologic unresponsiveness that may be specific or
general and attributable to products produced by selected
lymphocytes or by the administration of immunosuppressive
drugs such as for organ transplantation.
suppressor CD4 + T cells
Refer to regulatory CD4 + T cells.
suppressor cell
A lymphoid cell subpopulation that can diminish or suppress
the immune reactivity of other cells. An example is
the CD8 + suppressor T lymphocyte subpopulation detectable
by monoclonal antibodies and flow cytometry in
peripheral blood lymphocytes.
suppressor/inducer T lymphocyte
A subpopulation of T lymphocytes that fail to induce
immunosuppression but are claimed to activate suppressor
T lymphocytes.
suppressor macrophage
Macrophage activated by its response to an infection or
neoplasm in the host from which it was derived. It can block
immunologic reactivity in vitro through production of prostaglandins,
oxygen radicals, and other inhibitors produced
via arachidonic acid metabolism.
suppressor T cell factor (TSF)
A soluble substance synthesized by suppressor T lymphocytes
that diminishes or suppresses the functions of
other lymphoid cells. The suppressor factor downregulates
immune reactivity. TSF is also an abbreviation for suppressor
T cell factor.
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