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infectious mononucleosis syndromes 388 inflammatory mediator
EBV. Splenomegaly and chemical hepatitis may also be
present.
infectious mononucleosis syndromes
Conditions induced by viruses that produce an acute and
striking peripheral blood monocytosis and lead to symptoms
resembling those of infectious mononucleosis induced by
Epstein–Barr virus. Examples include herpes virus, cytomegalovirus,
HIV-1, HHV-6, and Toxoplasma gondii infections.
infectious tolerance
A state in which induced peripheral tolerance to a given
antigen is transmitted from an anergic T cell population to
a population of normal T cells that are rendered tolerant to
the same antigen. This phenomenon may be mediated by
regulatory T cells. Infectious tolerance was described in the
1970s. Animals rendered tolerant to foreign antigens were
found to possess suppressor T lymphocytes associated with
the induced unresponsiveness. Thus, self tolerance was postulated
to be based on the induction of suppressor T cells.
Noel Rose referred to this concept as clonal balance rather
than clonal deletion. Self antigens are considered to normally
induce mostly suppressor rather than helper T cells,
leading to a negative suppressor balance in the animal body.
Three factors with the potential to suppress immune reactivity
against self include nonantigen-specific suppressor T
cells, antigen-specific suppressor T cells, and anti-idiotypic
antibodies. Rose suggested that suppressor T lymphocytes
leave the thymus slightly before the corresponding helper T
cells. Suppressor T cells specific for self antigens are postulated
to be continuously stimulated and usually in greater
numbers than the corresponding helper T cells.
infertility, immunological
Infertility in 12 to 25% of cases in which infertile couples
are unable to conceive even though they manifest no significant
abnormalities upon physical examination. These cases
of unexplained infertility may be caused by autoimmune
responses to organ-specific antigens of the reproductive
tracts of both males and females and isoimmune reactions
of females against semen components. Immune responses
may cause or contribute to infertility in approximately 10%
of these couples.
inflammation
A defense reaction of living tissue to injury. Plays an
integral role in both innate and adaptive immunity.
Inflammatory cells phagocytize antigen, generate chemical
signals that facilitate wound healing, and secrete
cytokines and chemokines that attract and regulate
lymphocytes. The literal meaning of the word is burning,
and it originates from the cardinal symptoms of rubor,
calor, tumor, and dolor, the Latin terms equivalent to redness,
heat, swelling, and pain, respectively. Inflammation
is beneficial for the host and essential for survival of the
species, although in some cases the response is exaggerated
and may be itself injurious. Inflammation is the
result of multiple interactions that have as a first objective
localization of the process and removal of the irritant.
This is followed by a period of repair. Inflammation
is not necessarily of an immunologic nature, although
immunologic reactions are among the immediate causes
inducing inflammation and the immunologic status of
the host determines the intensity of the inflammatory
response. Inflammation tends to be less intense in infants,
whose immune systems are not fully mature. The causes
of inflammation are numerous and include living microorganisms
such as pathogenic bacteria and animal parasites
that act mainly by the chemical poisons they produce and
less by mechanical irritation; viruses that become offenders
after they multiply in the host and cause cell damage;
and fungi that grow at the surface of the skin but produce
little or no inflammation in the dermis. Other causes of
inflammation include physical agents such as trauma, thermal
and radiant energy, and chemical agents that represent
a large group of exogenous or endogenous causes including
immunologic offenders. Mediators of inflammation
include kinins, acute phase proteins, leukotrienes, prostaglandins,
and vasoactive amines including histamine.
Refer to inflammatory response.
inflammatory bowel disease (IBD)
A general term that applies to ulcerative colitis, Crohn’s
disease, and idiopathic inflammatory bowel disease that
resembles the other two. There is a hereditary predisposition
to IBD. Intestinal epithelial cells express HLA-DR
(MHC class II) antigens in Crohn’s disease, ulcerative
colitis, and infectious colitis patients that may render the
antigens capable of becoming autoantigen-presenting cells.
Inflammatory bowel disease patients may become sensitized
to cow’s milk antigens, developing IgG and IgM antibodies
against this protein. Leukotrienes have been shown
to be of greater significance than prostaglandins in mediating
inflammation in ulcerative colitis. Mucocutaneous
conditions such as oral ulcers, epidermolysis bullosa
acquisita, erythema nodosa, etc., and eye diseases such
as uveitis and iridocyclitis may be associated with IBD.
Some IBD patients may also have cirrhosis, chronic active
hepatitis, or joint involvement such as ankylosing spondylitis.
IBD patients may have abdominal pain, fever, and
diarrhea. Granulomas may develop in the gut wall, and
lymphocytes that stain for IgA in the cytoplasm are often
abundant. Autoantibodies reactive with fetal colon antigens
may be present. IBD develops in gene knockout mice
lacking interleukin-2 (IL2), IL10, or the TCR-α chain.
Inflammation is mediated in part through the action of
cytokines that include IL1α, IL1β, IL6, or tumor necrosis
factor α (TNF-α). IL1α and IL1β induce fever, stimulate
acute phase protein synthesis, and activate the immune system.
TNF-α and IL6 enhance cellular catabolism, induce
acute phase proteins, and stimulate pyrogenic activity.
TNF-α can induce IL1 and IL6. TNF-α and IL2 stimulate
prostaglandin I 2 (PGIL 2), prostaglandin E (PGE 2), and
platelet-activating factor (PAF) secretion.
inflammatory CD4 T cell
Armed effector T H1 cell that synthesizes interferon γ
(IFN-γ) and tumor necrosis factor (TNF) cytokines when it
recognizes antigen. Its principal function is to activate macrophages.
Selected T H1 cells may also mediate cytotoxicity.
inflammatory cells
Cells of the blood and tissues that participate in acute and
chronic inflammatory reactions. They include polymorphonuclear
neutrophils, eosinophils, and macrophages.
inflammatory macrophage
A macrophage in a peritoneal exudate induced by thioglycolate
broth or mineral oil injection into the peritoneal
cavity of an experimental animal.
inflammatory mediator
A substance that participates in an inflammatory reaction.