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Sips distribution 656 Sjögren’s syndrome
Plot of Sips distribution function.
Sips distribution
Frequency distribution of antibody association constants
in a heterogeneous mixture. The Sips distribution is very
similar to Gaussian (normal) distribution. It is employed to
analyze data from antigen–antibody reactions measured by
equilibrium dialysis.
Sips plot
Data representation produced in assaying ligand binding to
antibodies by plotting log r/(n – r) against log c. A straight line
signifies that the data are in agreement with the Sips equation.
The slope signifies heterogeneity of antibody affinity.
sirolimus
A powerful immunosuppressive drug derived from a soil
fungus, Streptomyces hygroscopicus, on Rapa Nui (Easter
Island), also known as rapamycin. It binds immunophilins
and inhibits calcineurin and resembles FK506 in structure,
but has a different mechanism of action. It does not
inhibit interleukin synthesis by activated T cells; it blocks
responses of T cells to cytokines. It suppresses B and T
lymphocyte proliferation, lymphokine synthesis, and T
cell responsiveness to interleukin-2 (IL2). It is a powerful
inhibitor of B cell proliferation and immunoglobulin
synthesis. It blocks the mononuclear cell proliferative
response to colony-stimulating factors. It is effective as an
immunosuppressant when used alone or in combination
with other agents such as corticosteroids, cyclosporine,
tacrolimus, and mycophenolate mofetil in preventing rejection
of solid organ allografts. It may be useful in treating
steroid-refractory acute and chronic graft-vs.-host disease
in hematopoietic stem cell transplant recipients. Sirolimuseluding
coronary stents have been used effectively to reduce
restenosis in patients with advanced coronary artery disease,
due to its antiproliferative effects. Myelosuppression,
hepatotoxicity, diarrhea, and hypertriglyceridemia are toxic
effects. To achieve clinical immunosuppression, rapamycin
is effective at concentrations one eighth those required
for FK506 and 1% of the levels required for cyclosporin.
An immunosuppressive agent that inhibits T lymphocyte
activation and proliferation that occurs following antigenic
and cytokine (IL2, IL4, and IL15) stimulation by a mechanism
distinct from other immunosuppressive agents. It also
inhibits antibody production. Sirolimus binds to immunophilin
in cells, FK binding protein-12 (FKBP-12), to form
an immunosuppressive complex. The sirolimus:FKBP-12
complex affects calcineurin activity. It binds to and inhibits
activation of mTOR, the mammalian target of rapamycin,
an important regulatory kinase. This blockage suppresses
cytokine-driven T cell proliferation, resulting in inhibition
of G 1 to the S phase of the cell cycle. It prolongs survival
of allografts of kidney, heart, skin, islet, small bowel, pancreatic–duodenal,
and bone marrow transplants, reverses
acute rejection of heart and kidney allografts in rats, and
prolongs graft survival in presensitized rats. In selected
studies, the immunosuppressive effect lasted up to 6 months
after therapy was discontinued, representing an alloantigenspecific
tolerization effect. It has also been used in animal
models of autoimmune disease.
SIRS
Abbreviation for soluble immune response suppressor.
site-directed mutagenesis
A laboratory procedure that involves the substitution of
amino acids in a protein whose function is defined for the
purpose of localizing a certain activity.
SIV (simian immunodeficiency virus)
A lentivirus of primates that resembles human immunodeficiency
virus 1 (HIV-1) and HIV-2 in morphology and
attraction to cells that bear CD4 molecules such as lymphocytes
and macrophages. SIV also shares with these human
viruses the additional genes lacking in other retroviruses,
including vip, rev, upr, tat, and nef. SIV induces the classic
cytopathologic alterations of the type produced by HIV,
and can also induce chronic disease following a lengthy
latency. SIVmac239 is an SIV clone that induces a disease
resembling acquired immune deficiency syndrome (AIDS)
in monkeys.
SIV mac
Simian immunodeficiency virus capable of infecting
macaque monkeys.
Sjögren’s syndrome. Salivary gland. Antibody to ductal epithelium.
Sjögren’s syndrome
A condition in which immunologic injury to the lacrimal
and salivary glands leads to dry eyes (keratoconjunctivitis
sicca) and dry mouth (xerostomia). The condition may
occur alone as sicca syndrome (primary form) or with an
autoimmune disease such as rheumatoid arthritis (secondary
form). The lacrimal and salivary glands show extensive
lymphocytic infiltration and fibrosis. Most of the infiltrating
cells are CD4 + T cells, but some B cells (plasma cells)
that form antibody are present. Approximately 75% of the
patients form rheumatoid factor. The lupus erythematosus