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sia test (historical) 652 side chain theory
Ventral view of a rabbit in which the localized Shwartzman reaction was
induced with endotoxin. Note hemorrhage and necrosis.
Shwartzman reaction may be induced by two sequential
exposures to LPS or IL-1.
sia test (historical)
A former qualitative test for macroglobulinemia in which
patient serum was placed in water in one tube and in saline
in another tube. Precipitation of the serum in water attributable
to the low water solubility of immunoglobulin M (IgM)
but not in saline constituted a positive test.
sialophorin (CD43)
A principal glycoprotein present on the surfaces of thymocytes,
T cells, selected B lymphocytes, neutrophils, platelets,
and monocytes. Monocyte and lymphocyte sialophorin
is a 115-kDa polypeptide chain. The platelet and neutrophil
sialophorin is a 135-kDa polypeptide chain that differs from
the first form only in carbohydrate content. Galactose β1–3
galactosamine in O-linked saccharides bound to threonine
or serine amino acid residues represents a site of attachment
for sialic acid in thymocytes in the medulla and in mature
T cells. Incomplete sialylation of thymocytes in the thymic
cortex accounts for their binding to peanut lectin. The more
thoroughly sialylated structures on T cells and thymocytes
in the medulla fail to bind lectin. In humans, the sialophorin
molecule is composed of 400 amino acid residues: a
235-residue extracellular domain, a 23-residue transmembrane
portion, and a 123-residue domain in the cytoplasm.
Antibodies specific for CD43 can activate T cells. The
T cells of patients with Wiskott–Aldrich syndrome have
defective sialophorin.
sicca complex
A condition characterized by dryness of mucous
membranes, especially of the eyes, producing
keratoconjunctivitis attributable to decreased tearing that
results from lymphocytic infiltration of the lachrymal
glands, and by dry mouth (xerostomia), associated with
decreased formation of saliva as a result of lymphocytic
infiltration of the salivary glands producing obstruction of
the duct. Sicca complex is most frequently seen in patients
with Sjögren’s syndrome, but it also may be seen in sarcoidosis,
amyloidosis, hemochromatosis, vitamin A and C
deficiencies, scleroderma, and hyperlipoproteinemia types
IV and V.
sicca symptoms
Symptoms marked by dry eyes leading to blurry vision, dry
mouth (xerostomia) and dry throat, leading to swallowing
difficulties, and dry nose and skin.
Paul Ehrlich’s side-chain theory, developed in 1900, was the first selective
theory of antibody synthesis. Although elaborate in detail, the essential
feature of the theory was that cells of the immune system possess the
genetic capability to react to all known antigens and that each cell on the
surface bears receptors with surface haptophore side chains. On combination
with antigen, the side chains would be cast off into the circulation and
new receptors would replace old ones. These cast-off receptors represented
antibody molecules in the circulation. Although far more complex than this
explanation, the importance of the theory was in the amount of research
stimulated trying to disprove it. Nevertheless, it was the first effort to
account for the importance of genetics in immune responsiveness at a time
when Mendel’s basic studies had not yet been rediscovered by De Vries.
side chain theory
In 1899, Paul Ehrlich postulated that a cell possessed highly
complex chemical aggregates with attached groupings or
side chains whose normal function was to anchor nutrient