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immune response (Ir) genes 359 immunity to extracellular bacteria
characterized by the production of chemical mediators at the
site of injury. In addition to the adaptive immune response
described above, animals have innate or natural immunity present
from birth and designed to protect the host from injury or
infection without previous contact with the infectious agent or
antigen. It includes such protective factors as the skin, mucous
membranes, lysozyme in tears, stomach acid, and other factors.
Phagocytes, natural killer cells, and complement represent key
participants in natural innate immunity. The immune response
consists of a recognition stage in which the inducing agent is
identified as nonself or dangerous to self and an effector stage
aimed at elimination of the immunogen.
immune response (Ir) genes
Genes that regulate immune responsiveness to synthetic
polypeptide and protein antigens as demonstrated in
guinea pigs and mice. This property is transmitted as an
autosomal-dominant trait that maps to the major histocompatibility
complex (MHC) region. Ir genes control
helper T lymphocyte activation required for the generation
of antibodies against protein antigens. T lymphocytes
with specific receptors for antigen fail to recognize free
or soluble antigens, but they do recognize protein antigens
noncovalently linked to products of MHC genes termed
MHC class I and class II molecules. The failure of certain
animal strains to respond may be due to ineffective antigen
presentation in which processed antigen fails to bind
properly to MHC class II molecules or to an ineffective
interaction between the T cell receptor and the MHC class
II–antigen complex.
immune serum
An antiserum containing antibodies specific for a particular
antigen or immunogen. Such antibodies may confer protective
immunity.
immune serum globulin
Injectable immunoglobulin that consists mainly of IgG
extracted by cold ethanol fractionation from pooled plasma
from up to 1000 human donors. It is administered as a sterile
16.5 ± 1.5% solution to patients with immunodeficiencies
and as a preventive against certain viral infections including
measles and hepatitis A.
immune stimulatory complexes
Refer to ISCOMs.
immune suppression
Decreased immune responsiveness as a consequence of therapeutic
intervention with drugs or irradiation or arising from
a disease process that adversely affects the immune response,
such as acquired immune deficiency syndrome (AIDS).
immune surveillance
The policing function of immune system cells to identify
and destroy clones of transformed cells prior to their development
into neoplasms and to destroy tumors after they
develop. Indirect evidence for this concept has included
observations that the incidence of neoplasia increases
with age-associated decrease in immune competence, the
development of tumors in T cell-deficient subjects, and
increased incidence of tumor development in deliberately
immunosuppressed individuals, such as those receiving
organ allotransplants.
immune system
The molecules, cells, tissues, and organs associated with
adaptive immunity, such as the host defense mechanisms,
mainly against infectious agents.
Microorganism Cell Type
Extracellular bacteria Polymorphonuclear
neutrophils (PMNs)
Parasites
Eosinophils
Intracellular
Macrophages
microorganisms
(i.e., mycobacteria or
fungi)
Viruses
Lymphocytes, NK cells
Nonspecific cellular defense.
immune system anatomy
The lymphocyte is the cell responsible for immune response
specificity. The human mature lymphoid system is comprised
of 2 × 10 12 lymphocytes and various accessory cells that
include epithelial cells, monocytes/macrophages, and other
antigen-presenting cells. Accessory cells are requisite for
both maturation and effector functions of lymphocytes. The
thymus is the site of maturation of T cells, and the bone marrow
is the maturation site of B cells. These two tissues comprise
the primary lymphoid organs. The secondary lymphoid
organs consist of the cervical lymph nodes, ancillary lymph
nodes, spleen, mesenteric lymph nodes, and inguinal lymph
nodes. Mature lymphocytes migrate from the central lymphoid
organs by way of the blood vessels to the secondary or
peripheral tissues and organs, where they respond to antigen.
Peripheral lymphoid tissues comprise the spleen and lymph
nodes and mucosa-associated lymphoid tissue (MALT)
associated with the respiratory, genitourinary, and gastrointestinal
tracts making up 50% of the lymphoid cells of the
body. MALT consists of the adenoids, tonsils, and mucosaassociated
lymphoid cells of the respiratory, genitourinary,
and gastrointestinal tracts, and Peyer’s patches in the gut.
immune tolerance
Refer to immunologic tolerance.
immunity
Acquired or innate resistance or protection from a pathogenic
microorganism or its products or from the effects of
toxic substances such as snake or insect venom.
immunity deficiency syndrome
Synonym for immunodeficiency.
immunity in prokaryotes
Numerous antimicrobial agents synthesized and released
extracellularly by bacteria exert specific effects on bacteria.
They 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. Once these agents are inside bacterial
cells they must remain unchanged to exert their actions.
Bacteriocins released by bacteria may inhibit the growth of
other sensitive closely related bacteria. The strain producing
the bacteriocin is usually able to resist its effect through
specific immunity peptides or proteins.
immunity to extracellular bacteria
Neutrophil (PMN), monocyte, and tissue macrophage
phagocytosis leads to rapid microbial action against ingested
microbes from the extracellular environment. The capacity
of a microorganism to resist phagocytosis and digestion
in phagocytic cells is a principal feature of its virulence.
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