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privileged site 594 progressive systemic sclerosis
Private antigen
Public antigen
Public and private antigens.
privileged site
Anatomical location protected from immune effector
mechanisms because of the absence of normal lymphatic
drainage. Antigenic substances such as tissue allografts
may be placed in these sites without evoking immune
responses. Privileged sites include the anterior chamber
of the eye, the cheek pouch of the Syrian hamster, and the
central nervous system. Tissue allografts in these locations
enjoy a period of protection from immunologic rejection,
as the diffusion of antigen from graft sites to lymphoid
tissues is delayed. Immune privilege alters the induction of
immunity to antigens first encountered via privileged sites
and also inhibits the expression of certain forms of alloimmunity
in these same sites.
pro-B cell (progenitor B cell)
Cells that have displayed B cell surface marker proteins
but have not yet completed heavy chain gene rearrangement.
They are divided into early and late pro-B cells.
The earliest stage of B cell development in which a heavy
chain D gene segment rearranges to a J gene segment. D H
to J H joining takes place at the early pro-B cell state and is
followed by V H to DJ H joining at the late pro-B cell stage.
Pro-B cells fail to produce immunoglobulin and express B
lineage-restricted surface markers that include CD19 and
CD10.
probe hybridization (tissue typing)
A technique used in tissue typing for organ transplantation
in which total DNA is isolated from a subject’s cells and
PCR is conducted with primers that permit generic amplification
of all HLA alleles. Hybridization to allele-specific
probes permits the identification of sequences of interest.
pro-C3
A polypeptide single chain split into C3 α and β (amino
terminal) chains.
pro-C4
A polypeptide single chain split into C4 α, β (amino terminal)
and γ (carboxyl terminal) chains.
pro-C5
A polypeptide single chain split into C5 α and β (amino
terminal) chains.
procomplementary factors
Serum components of selected species such as swine that
resemble complement in their action and confuse evaluation
of complement fixation tests.
prodrug
A therapeutic agent that is biologically inactive until
metabolized in the body to yield an active drug.
productive infection
An infection in which a pathogenic microorganism proliferates
even in the presence of an immune response against it.
productive rearrangement
Immunoglobulin and T cell receptor gene DNA rearrangements
that yield a gene capable of governing the production
of a functional polypeptide chain.
productivity testing
An assay that involves developing B or T cells of a specific
V(D)J combination’s functionality by transcribing the newly
constructed gene and translating its mRNA. Along with accessory
proteins of the pre-B cell receptor or pre-T cell receptor,
the chain of interest is expressed on the cell surface and sends
a signal to the cell confirming successful recombination.
proenzyme
An inactive enzyme precursor (or zymogen) frequently triggered
by enzymatic cleavage in a molecular cascade as in
the activation of complement.
professional APC
Refer to professional antigen-presenting cells.
professional antigen-presenting cells
Dendritic cells, macrophages, and B cells capable of initiating
responsiveness of naïve T lymphocytes to antigen.
These cells display antigenic peptide fragments in association
with the proper class of major histocompatibility
complex (MHC) molecules and also bear costimulatory
surface molecules. Dendritic cells are the most important
professional antigen-presenting cells (APCs) for initiating
primary T lymphocyte responses.
progenitor cell
A cell no longer containing the capacity for self renewal and
which is committed to the generation of a specific cell lineage.
programmed cell death
Apoptosis in which death is activated from within a dying
cell. It occurs in lymphocytes deprived of growth factors or
costimulators. It is also known as “death by neglect” and
“passive cell death,” in which mitochondrial cytochrome c
is released into the cytoplasm, caspase-9 is activated, and
apoptosis is initiated. Refer to apoptosis.
progressive multifocal leukoencephalopathy
A central nervous system disease characterized by demyelination,
very little inflammation associated with patches
of cortical degeneration, oligodendrogliocytes, intranuclear
viral inclusions, aberrant large astrocytes, and reactive
fibrillary astrocytes. This condition occurs in immunosuppressed
individuals such as those with AIDS or latent virus
infections such as measles. Papovavirus (DNA type, often
JC) usually causes it.
progressive systemic sclerosis
A connective tissue or collagen-vascular disease in
which the skin and submucosal connective tissue become
thickened and scarred. Collagen deposition in the skin is
increased. The disease is slowly progressive and chronic and
may involve internal organs. The female-to-male ratio is
2:1. Although the etiology is unknown, patients demonstrate
antinuclear antibodies, rheumatoid factor, and polyclonal
hypergammaglobulinemia. No demonstrable immunoglobulin
is found at the dermal–epidermal junction. Patients
may have altered cellular immunity. The epidermis is thin,