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sarcoma 636 scavenger receptors
Open lung biopsy showing sarcoidosis.
geographically in the southeastern United States. It exhibits
a decrease in circulating T cells. Decreased delayedtype
hypersensitivity is manifested as anergy to common
skin test antigens. Increased antibody formation leads to
polyclonal hypergammaglobulinemia. A marked cellular
immune response is observed in local areas of disease activity.
Tissue lesions consist of inflammatory cells and granulomas
composed of activated mononuclear phagocytes such
as epithelioid cells, multinucleated giant cells, and macrophages.
Activated T cells are present at the periphery of
the granuloma. CD4 + T cells appear to be the immunoregulatory
agents governing granuloma formation. Mediators
released from T cells nonspecifically stimulate B cells,
resulting in the polyclonal hypergammaglobulinemia. The
granulomas are typically noncaseating, distinguishing them
from those produced in tuberculosis. Patients may develop
fever, polyarthritis, erythema nodosum, and iritis. They also
may experience loss of weight, anorexia, weakness, fever,
sweats, nonproductive cough, and increasing dyspnea on
exertion. Pulmonary symptoms occur in more than 90% of
patients. Angiotensin-converting enzyme is increased in the
sera of sarcoid patients. Disease activity is monitored by
measuring the level of this enzyme in serum. The subcutaneous
inoculation of sarcoidosis lymph node extracts into
patients diagnosed with sarcoidosis leads to a granulomatous
reaction in the skin 3 to 4 weeks after inoculation. This
served as a diagnostic test of questionable value (known
as the Kveim reaction) in the past. Sarcoidosis symptoms
can be treated with corticosteroids, but only after disease
progression occurs. Sarcoidosis is a relatively mild disease,
with 80% of cases resolving spontaneously and only 5%
dying of complications. Evidence indicates oligoclonal
expansion of αβ T cell subsets and predominant expression
of type 1 cytokines—interferon-γ (IFN-γ) and interleukin-2
(IL1-2)—at sites of inflammation, suggesting that sarcoidosis
is an antigen-driven, Th1-mediated immune disorder.
sarcoma
A malignant neoplasm arising from connective tissue cells
including muscle, bone or cartilage.
Sca-1
Abbreviation for stem cell antigen 1.
SCABs (single-chain antigen-binding proteins)
Polypeptides that join the light chain variable sequence of
an antibody to the heavy chain variable sequence of the
antibody. All monoclonal antibodies are potential sources
of SCABs. They are smaller and less immunogenic than
intact heavy chains with immunogenic constant regions.
Their potential uses include imaging and treatment of
cancer, in cardiovascular disease, as biosensors, and for
chemical separations.
scarlet fever
A condition associated with production of erythrogenic
toxin by group A hemolytic streptococci associated with
pharyngitis. Patients develop strawberry-red tongues and
generalized erythematous blanching areas that do not occur
on the palms, the soles of the feet, or in the mouth. They
may also develop Pastia’s lines (petechiae in linear patterns).
Scatchard analysis
A mathematical analytical method to determine the affinity
and valence of a receptor–ligand interaction in equilibrium
binding.
Scatchard equation
An expression for the union of a univalent ligand with an
antibody molecule (r/c = Kn – Kr). To obtain the average
number of ligand molecules to which an antibody molecule
may bind at equilibrium, the bound ligand molar
concentration is divided by the antibody molar concentration
designated as r. The free ligand molar concentration is
represented by c; antibody valence by n; and the association
constant by K.
d
(Ag)
d
d
(Ag)
Scatchard plot
A graphic representation of binding data obtained by
plotting r/c against r (refer to Scatchard equation). The
purpose of this plot is to determine intrinsic association
constants and ascertain how many noninteracting binding
sites each molecule contains. A straight line with a slope of
–K indicates that all the binding sites are the same and are
independent. The plot should also intercept on the r axis of
n. A nonlinear plot signifies that the binding sites are not
the same and are not independent. The degree to which the
sites are occupied is reflected by the slope (–K). An average
association constant for ligand binding to heterogeneous
antibodies is the reciprocal of the amount of free ligand
needed for half saturation of antibody sites.
scavenger receptors
Structures on macrophages and other cell types that
bind a variety of ligands and delete them from the blood.
Scavenger receptors are especially abundant on Kupffer’s
cells of the liver.
d
Scatchard plot.
=–K
x - intercept