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signal sequence 654 single cysteine motif-1 (SCM-1)
signal sequence
Refer to signal hypothesis.
signal transducer and activator of transcription (STAT)
A protein signaling molecule and transcription factor in
response to cytokines binding to type I and type II cytokine
receptors. STATs exist as inactive monomers in cell cytoplasm
and are transported to cytoplasmic tails of cross linked
cytokine receptors where they are tyrosine-phosphorylated by
Janus kinases (Jaks). Phosphorylated STAT proteins dimerize
and migrate to nuclei where they bind to specific sequences in
the promoter regions of various genes and activate their transcription.
Different cytokines activate different STATs.
signal transduction
Process whereby signals received on cell surfaces, such as
by the binding of antigen to its receptor, are transmitted into
cell nuclei, resulting in altered gene expression.
silencer sequence
Blocks transcription of the T cell receptor α chain. This
sequence is found 5′ to the α chain enhancer in non-T cells
and in those with γδ receptors.
silencers
Nucleotide sequences that downregulate transcription,
functioning in both directions over a distance.
silica adjuvants
Silica crystals and hydrated aluminum silicate (bentonite)
were occasionally used in the past to enhance immune
responses to certain antigens. They were considered to exert
a central action on the immune system rather than serving as
depot adjuvants, although bentonite can delay the distribution
of antigen from its site of inoculation by surface adsorption.
silicate autoantibodies
Autoantibodies stimulated by silicone plastic polymers used
for breast implants in cosmetic and reconstructive surgery,
vascular prostheses, and joint repair and replacement.
Silicone-induced human adjuvant diseases characterized
by autoimmune-disease-like symptoms, granulomas, and
serological abnormalities have been reported since 1964.
Some individuals with breast and joint implants reportedly
developed delayed-type hypersensitivity to silicone plastic
as interpreted by refractile particles in phagocytes and
passage between lymphocytes and macrophages. Women
who develop implant ruptures or leakage of silicone gel
implants may develop high titers of silicone autoantibodies
as measured using silicate-coated plates in enzyme
immunoassay (EIA). Only 4% of 249 patients with silicone
breast implants developed immunoglobulin G (IgG) binding
to fibronectin–laminin adsorbed to silicone and only 2%
showed IgG binding to silicone film alone. Thus, patients
occasionally develop antibodies against fibronectin and
laminin denatured by silicone. Whereas 30% of 40 of
symptomatic women with silicone breast implants formed
IgG antibodies that reacted with bovine serum albumin
(BSA)-bound silicate, 9% (8 of 91) of asymptomatic patients
with silicone breast implants also formed these antibodies
in low concentrations.
silicosis
The inhalation of silica particles over a prolonged period
produces a chronic, nodular, densely fibrosing pneumoconiosis
that has an insidious onset and progresses even in the
absence of continued exposure to silica dust. Lymphocytes
and alveolar macrophages are quickly attracted to the
particles that are phagocytized by the macrophages. Some
macrophages remain in the interstitial tissue or pulmonary
lymphatic channels. Interaction of macrophages and
silica particles leads over time to collagenous fibrosis and
fibrosing nodules. The silica dust–macrophage interaction
may cause the secretion of interleukin-1 (IL1) that recruits
T helper cells producing IL2, which induces proliferation
of T lymphocytes that in turn produce a variety of
lymphokines. Thus, immunocompetent cells mediate the
collagenous reaction. Activated T cells interact with B lymphocytes
that synthesize increased amounts of IgG, IgM,
rheumatoid factor, antinuclear antibodies, and circulating
immune complexes. Collagenous silicotic nodules may
coalesce, producing fibrous scars. The disease may be complicated
by rheumatoid arthritis, pulmonary tuberculosis,
emphysema, and other diseases. No increased incidence of
lung cancer is associated with silicosis.
simian immunodeficiency virus (SIV)
This virus causes a disease resembling human acquired
immune deficiency syndrome (AIDS) in rhesus monkeys.
The SIV sequence reveals significant homology with human
immunodeficiency virus 2 (HIV-2), a cause of AIDS in
western Africa.
Simonsen phenomenon
A graft-vs.-host reaction in chick embryos that develop
splenomegaly following inoculation of immunologically
competent lymphoid cells from adult chickens. Splenic
lymphocytes are increased and represent a mixture of both
donor and host lymphocytes.
simple allotype
An allotype that differs from another allotype in the
sequence of amino acids at one or several positions. Alleles
at one genetic locus often encode simple allotypes.
Simulect (basiliximab)
A chimeric (murine–human) monoclonal antibody (IgG 1k),
produced by recombinant DNA technology that functions
as an immunosuppressive agent, specifically binding to
and blocking the interleukin-2 receptor α (IL2Rα; also
known as CD25 antigen) chain on the surfaces of activated
T lymphocytes. Based on the amino acid sequence, the
calculated molecular weight of the protein is 144 kDa. It is
a glycoprotein obtained from fermentation of an established
mouse myeloma cell line genetically engineered to express
plasmids containing the human heavy and light chain constant
region genes and mouse heavy and light chain variable
region genes encoding the RFT5 antibody that binds
selectively to IL2Rα. Basiliximab (the active ingredient) is
water-soluble. The Simulect product is a sterile lyophilisate
available in 6-mL colorless glass vials. Each vial contains
20 mg basiliximab, 7.21 mg monobasic potassium phosphate,
0.99 mg disodium hydrogen phosphate (anhydrous),
1.61 mg sodium chloride, 20 mg sucrose, 80 mg mannitol,
and 40 mg glycine to be reconstituted in 5 mL of sterile
water for injection, USP. No preservatives are added.
single chain Fv fragment
A genetically engineered structure consisting of a heavy
chain V region linked by a stretch of synthetic peptide to a
light chain V region.
single cysteine motif-1 (SCM-1)
A member of the γ (C) family of chemokines. cDNA clones
derived from human peripheral blood mononuclear cells
stimulated with PHA encode SCM-1, which is significantly
related to the α and β chemokines. It has only the second