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escue graft 618 resting lymphocytes
Reptile immunity.
seasonal temperature and other environmental conditions;
otherwise, it may reveal degrees of degeneration. The
spleen is the most significant peripheral lymphoid organ
in reptiles. It becomes lymphopoietic much later than the
thymus in lizards, snakes, and tortoises; 50 to 70% of reptile
splenic lymphocytes are thymus-derived and located in
thymus-dependent areas. Reptiles do not develop germinal
centers and nodules found in mammalian secondary lymphoid
organs. T and B cell-like cells differ in their sensitivity
to environmental conditions. Gut-associated lymphoid
tissue (GALT) develops in lizards, snakes, and chelonians.
Reptiles do not have tonsils, Peyer’s patches, or appendices;
they have numerous lymphoid aggregates in the mucosa
and submucosa along the gut. In lizards, the esophageal
lymphoid aggregates containing T cell-like lymphocytes
are greatly affected by seasonal and environmental conditions,
whereas the B cell-like cells and GALT in reptiles
are resistant to changes in season. The spleen and GALT
carry out humoral immune mechanisms. Although reptiles
do not have true lymph nodes, their lymphoid systems are
homologous to those of mammals except for high sensitivity
to ambient conditions. Reptile lymphocytes are strongly
responsive to plant mitogens. Lizards and snakes reject skin
grafts in a manner similar to mammals. Reptiles also manifest
major functional markers of the major histocompatibility
complex (MHC). They produce at least two classes
of immunoglobulin (Ig) that resemble IgM and a second
immunoglobulin of lower molecular weight that is antigenically
related to the 7S Ig of birds and amphibians. All
reptiles can mount powerful immune responses to various
antigens that include bacteria, protozoa, erythrocytes, and
proteins. Body temperature is a critical regulator of immune
function. Reptiles, in contrast to fish and amphibians, are
restricted in the temperature range over which immune
responses can occur.
rescue graft
A replacement graft for an original graft that failed.
reservoir
A host or carrier that harbors pathogenic microorganisms
without being injured itself; it serves as a source of infection
for others. Also termed reservoir host or reservoir of infection.
resident macrophage
A macrophage normally present at a tissue location without
being induced to migrate there.
respiratory burst
A process used by neutrophils and monocytes to kill certain
pathogenic microorganisms. It involves increased oxygen
consumption with the generation of hydrogen peroxide
and superoxide anions. This occurs also in macrophages
that kill tumor cells. Respiratory burst is characterized
by an abrupt elevation in oxygen consumption, followed
by metabolic events in neutrophils and mononuclear cells
preceding bacteriolysis. Partial reduction of oxygen by this
process provides microbicidal oxidants. The initial event
is a one-electron reduction of oxygen by membrane-bound
oxidase to form a superoxide. The hexose monophosphate
shunt reaction that accompanies this reduction liberates an
H + that unites with the oxygen to produce H 2O 2. Following
neutrophil degranulation, NADPH-dependent oxidases
fixed to granule membranes activate the formation of inorganic
radicals and myeloperoxidase action, leading to the
generation of hypochlorous acid, causing the oxidation of
nucleic acids, amino acids, and thiols of the microbe. The
respiratory burst is reflected in the increased use of oxygen
by NADPH oxidases to maintain this antimicrobial activity.
respiratory disease viruses
Influenza, paramyxoviruses, rhinoviruses, pneumoviruses,
enteroviruses, coronaviruses, and mastadenoviruses that
induce infections of the respiratory tract in humans.
respiratory syncytial virus (RSV)
A frequent cause of severe chest infections in young children
who develop wheezing; a paramyxovirus.
respiratory syncytial virus (RSV) immunity
RSV is responsible for 70% of bronchiolitis cases, a common
cause of infant hospitalization. Immunoglobulin G
(IgG), IgM, and IgA antibodies are formed and can be
detected by enzyme immunoassay (EIA). Some heterologous
antibody responses occur in primary and recurrent
infections with groups A and B RSV. Diagnosis of acute
RSV infection is made by antigen detection in nasopharyngeal
secretions by fluorescent antibody or EIA methods.
responder animals
Guinea pigs immunized by DNP–PLL or DNP–GL produce
significant amounts of anti-DNP antibodies and develop
delayed-type hypersensitivity reactions to the conjugate.
Conversely, nonresponder animals produce few or no anti-
DNP antibodies and do not develop delayed-type hypersensitivity.
The capacity to respond to DNP–PLL antigen is
a function of a dominant autosomal gene. All guinea pigs
of strain 13 are nonresponders, whereas strain 2 guinea
pigs and (2 × 13) F 1 hybrids are responders. The immune
response gene present in strain 2 but absent in strain 13 is
called the PLL gene.
resting lymphocytes
Under light microscopy, resting lymphocytes appear as a
distinct and homogeneous population of round cells, each
with a large spherical or slightly kidney-shaped nucleus that
occupies most of the cell and is surrounded by a narrow
rim of basophilic cytoplasm with occasional vacuoles. The