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progressive transformation of germinal centers (PTGC) 595 prophylactic immunization
dermal appendages atrophy, and rete pegs are lost. Collagen
deposition is markedly increased in the reticular dermis,
and fibrosis and hyalinization of arterioles are present. The
gastrointestinal tract may also reveal increased collagen
deposition in the lamina propria, submucosa, and muscularis
layers. At the onset, 90% of affected individuals experience
Raynaud’s phenomenon. Skin changes are usually the
initial manifestations, with involvement of the hands, feet,
forearms, and face or possibly diffuse involvement of the
trunk. A variation of the disease called CREST syndrome
consists of calcinosis, Raynaud’s disease, esophageal
dysmotility, sclerodactyly, and telangiectasia. This form of
the disease may become stabilized for a number of years.
The skin may exhibit a tight, smooth, waxy appearance
in the sclerotic phase with no wrinkles or folds apparent.
Ulcers may develop on the fingertips in many patients with
a mask-like appearance of the face with thin lips. The skin
may become atrophic or return to a normal soft structure.
The lungs may be involved, leading to dyspnea on exertion.
Pulmonary fibrosis may lead to cor pulmonale. The principal
immunologic findings include antinuclear antibodies
with a speckled or nucleolar pattern, anticentromere antibodies
(in individuals with known CREST syndrome), and
the development of antibodies specific for acid-extractable
nuclear antigen. Approximately one third of the individuals
with diffuse involvement of the trunk reveal antibodies
specific for topoisomerase (anti-Scl-70 antibodies).
progressive transformation of germinal centers (PTGC)
Germinal center enlargement in the presence of follicular
hyperplasia and loss of the distinct boundary between the
mantle zone and the germinal center. Transformed germinal
centers contain small lymphocytes with diffuse immunoblasts
and histiocytes and often occur in one enlarged
lymph node in young men. It is not believed to be neoplastic
or portend development of lymphoma although it may be
observed in some patients with nodular lymphocyte-
predominant Hodgkin disease.
progressive vaccinia
An adverse reaction to smallpox vaccination in children
with primary cell-mediated immunodeficiency, such as
severe combined immunodeficiency. The vaccination lesion
spreads from the site of inoculation and covers extensive
areas of the body surface, leading to death.
prokaryote
An organism that contains one linear chromosome rather
than a true nucleus.
prokaryotes, immunity in
Numerous antimicrobial agents synthesized and released
extracellularly by bacteria exert specific effects on the bacteria.
The agents include (1) enzymatically synthesized antibiotics;
(2) post-translationally modified peptide antibiotics; (3)
protein antibiotics such as bacteriocins, protein exotoxins, and
bacteriolytic enzymes; and (4) intemperate or temperate bacterial
viruses. After these agents enter bacterial cells, they must
remain unchanged to exert their actions. Bacteriocins released
by bacteria may inhibit the growth of other sensitive closely
related bacteria, yet the strain producing the bacteriocin is usually
able to resist its effect through specific immunity peptides
or proteins. Antibiotic-synthesizing strains protect themselves
from their own products by forming immunity proteins.
Immunity to bacteriophage is the failure of an infected bacterial
cell to be reinfected by a phage of the same type. Colicins
and bacteriophages and many other substances facilitate
bacterial strain competitiveness. Immunity mechanisms are
very specific and depend on protein–protein, protein–DNA,
or RNA–DNA interactions. Numerous mechanisms confer
immunity to prokaryotic organisms against specific bactericidal
agents. Immunity also refers to replicons carrying
transposons. A duplicate of a transposon fails to insert into a
replicon already carrying a copy of the same transposon.
promiscuous binding
A docking site that accepts several different ligands with
related affinity manifests promiscuous binding.
promoter
(1) The DNA molecular site where RNA polymerase
attaches and transcription is initiated. The promoter is
frequently situated adjacent to the operator, and upstream
from it is an operon. A TATA box and a promoter are
both required for immunoglobulin gene transcription.
(2) In tumor biology, a promoter mediates the second or
promotion stage in the process of carcinogenesis. It may
be a substance that can induce a tumor in an experimental
animal that was previously exposed to a tumor initiator, but
the promoter alone is not carcinogenic.
properdin (factor P)
A globulin in normal serum that has a central role in activation
of the alternative complement pathway. Additional
factors such as magnesium ions are required for properdin
activity. Properdin is an alternative complement pathway protein
that is significant in resistance against infection. It combines
with and stabilizes the C3 convertase of the alternate
pathway which is designated C3bBb. It is a 441-amino acid
residue polypeptide chain with two points where N-linked
oligosaccharides may become attached. Electron microscopy
reveals it to have a cyclic oligomer conformation. Molecules
are composed of six repeating 60-residue motifs that are
homologous to 60 amino acids at C7, C8α, and C8β amino
carboxyl terminal ends and the C9 amino terminal end.
properdin deficiency
An X-linked recessive disorder involving increased susceptibility
to infections by Neisseria microorganisms. Males
with the deficiency reveal 2% or less of normal serum levels
of properdin. In some heterozygous females, the serum
properdin level may be only 50%, while in others serum
properdin levels are normal.
properdin pathway
An early synonym for alternative pathway of complement
activation.
properdin system
An early term for the alternative complement pathway that
consists of several proteins that are significant in resistance
against infection. The first protein to be discovered was
properdin. The properdin system also consists of factor
B, a 95-kDa β 2 globulin also known as C3 proactivator,
glycine-rich β glycoprotein, or β 2 glycoprotein II. Properdin
factor D is a 25-kDa α globulin also called C3 proactivator
convertase or glycine-rich β glycoproteinase. The properdin
system or alternative pathway does not require the
participation of antibody to activate complement. It may be
activated by endotoxin or other substances. See alternative
complement pathway.
prophylactic immunization
Prevention of disease through active or passive immunization.
Active immunization usually induces longer lasting protection.
P