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steric hindrance 668 Streptococcus immunity
Stem cell.
Striational autoantibodies.
individual cells can differentiate and proliferate under favorable
conditions. Pluripotent stem cells (CFU-S) are capable
of differentiating into committed precursor cells of the granulocyte
and monocyte lineage (CFU-C), of erythropoietic
lineage (CFU-E and BFUE), and of megakaryocyte lineage
(CFU-Mg). Lymphocytes, like other hematopoietic cells,
are generated in bone marrow. The stem cell compartment
is composed of a continuum of cells that includes the most
primitive, with the greatest capacity for self renewal and the
least evidence of cell cycle activity, to the most committed
with a lesser capacity for self renewal and the most evidence
of cell cycle activity. Stem cells are multipotential precursors
with the capacity to yield differentiated cell types with different
functions and phenotypes; however, their proliferative
capacity is limited.
steric hindrance
Interference between the interaction of the paratope of an
antibody molecule with the homologous epitopes on antigen
molecules of varying sizes based on the shapes of the two
reactants. Whereas IgM molecules potentially have an
antigen-binding capacity of ten, only some of these may be
able to interact with relatively large antigen molecules bearing
epitopes because of their shapes. By contrast, relatively
small antigen molecules may permit their epitopes to bind
with more paratopes on IgM molecules. Steric hindrance
also refers to the blocking of ligand binding when a receptor
site is already occupied by another ligand.
steric repulsion
Refer to van der Waals forces and London forces.
steroid cell antibodies
Immunoglobulin G (IgG) antibodies that interact with
antigens in the cytoplasm of cells, producing steroids in the
ovary, testes, placenta, and adrenal cortex. Patients with
Addison’s disease along with ovarian failure or hypoparathyroidism
develop these antibodies that are rarely associated
with primary ovarian failure in which organ-specific
and nonorgan-specific autoantibodies are prominent.
stiff man syndrome (SMS)
Progressive involuntary axial and lower limb rigidity
that disappears during sleep. It results from an imbalance
between descending inhibitory γ amino butyric acid
(GABA)-ergic and excitatory aminergic pathways. Sixty
percent of SMS patients have circulating antibody against
glutamic acid decarboxylase (GAD), an enzyme that has
65- and 67-kDa isoforms. GAD is a major antigenic target
in insulin-dependent diabetes mellitus (IDDM). Antibody
levels to GAD are 100- to 500-fold higher in SMS than in
IDDM. SMS anti-GADs bind to both linear epitopes and
epitopes that depend on protein conformation. SMS is associated
with other autoimmune diseases including myasthenia
gravis, pernicious anemia, vitiligo, autoimmune adrenal
failure, ovarian failure, thyroid disease, and IDDM.
stimulated macrophage
A macrophage activated in vivo or in vitro. Activated macrophage
is the preferred term.
stochastic models
Designs characterized by chance events without external
direction or regulation.
Stormont test
A double intradermal tuberculin test.
strain
Genetically identical animals such as mice or rats used in
medical research.
street virus
A natural or genetically unmodified virus such as rabies
that can be isolated from animals.
streptavidin
A protein isolated from streptomyces that binds biotin. This
property makes streptavidin useful in the immunoperoxidase
reaction used extensively in antigen identification in
histopathologic specimens, especially in surgical pathologic
diagnosis.
Streptobacillus immunity
Although immune responses are induced in subjects
infected with Streptobacillus moniliformis, the exact
mechanisms and relative contribution of antibody remain
to be determined. In mouse experiments, antibody confers
only partial immunity to challenge with the microorganism.
Inactivated S. moniliformis vaccines induce only partial
protection against challenge.
streptococcal M protein
A cell wall protein of virulent Streptococcus pyogenes
microorganisms that interferes with phagocytosis and also
serves as a nephritogenic factor.
Streptococcus immunity
The most effective host resistance against pneumococcal
(Streptococcus pneumoniae) infection is the synthesis of
immunoglobulin G (IgG) or IgM that interacts with capsular
polysaccharide, opsonizing the bacteria for ingestion and
killing by professional phagocytes. Anticapsular antibody
develops following colonization or infection. Most individuals
have low resistance as reflected by their lack of antibodies
to most of the commonly infecting pneumococcal serotypes
even though normal adults may have sufficient antibodies