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interfollicular region 398 interleukin-1 receptor (IL1R)
γ is acid-labile and is formed mainly by T lymphocytes
stimulated by antigen or mitogen. This immune interferon
was known as type II in the past. Whereas the ability of
interferon to prevent infection of noninfected cells is species-specific,
it is not virus-specific. Essentially, all viruses
are subject to its inhibitory action. Interferons induce
formation of a second inhibitory protein that prevents viral
messenger RNA translation. In addition to interferon γ
formation by T cells activated with mitogen, natural killer
cells also secrete it. Interferons are not viricidal.
interfollicular region
Tissue separating lymphoid follicles situated in a group; it
exhibits a predominance of mature T cells encircling high
endothelial venules (HEVs).
interleukin (IL)
A general term for numerous cytokines synthesized by leukocytes.
Includes multiple secreted proteins that facilitate
inflammation exchange among leukocytes and activate signaling
that regulates hematopoietic cell growth, differentiation,
and function.
Interleukin-1α.
interleukin-1 (IL1)
The two proteins comprising the IL1 molecule and designated
IL1α and IL1β belong to the interleukin-1 superfamily
of cytokine molecules. The molecules identified within
the IL1 superfamily include IL18 and cytokines encoded
by six more genes with structural homology to IL1α, IL1β,
or IL1RA. These latter six members are terned IL1F5
through IL1F10. IL1α, IL1β, and IL1RA are now known as
IL1F1, IL1F2, and IL1F3. IL33 is an additional member of
the IL1 family; it is also known as IL1F11. Macrophages,
monocytes and dendritic cells synthesize IL1α and IL1β,
which constitute significant parts of the body’s inflammatory
response to infection. These cytokines elevate adhesion
molecule expression on endothelial cells to facilitate
transmigration of leukocytes to sites of infection and reset
the hypothalamus thermoregulatory center, which causes
an elevation in body temperature manifested as fever. Thus,
IL1 is an endogenous pyrogen. IL1 also plays a significant
role in regulation of hematopoiesis. IL1 is a cytokine synthesized
by activated mononuclear phagocytes stimulated
by ribopolysaccharide or by interaction with CD4 + T lymphocytes.
It is a monokine and a mediator of inflammation,
sharing many properties in common with tumor necrosis
factors (TNFs). IL1, IL6, and TNF-α induce a variety
Interleukin-1β.
of inflammatory responses early during infection. IL1 is
composed of two principal polypeptides of 17 kDa, each
with isoelectric points of 5.0 and 7.0. They are designated
IL1α and IL1β, respectively. Genes found on chromosome
2 encode these two molecular species. They have the same
biological activities and bind to the same receptors on cell
surfaces. Both IL1α and IL1β are derived by proteolytic
cleavage of 33-kDa precursor molecules. IL1α acts as a
membrane-associated substance, whereas IL1β is found free
in the circulation. IL1 receptors are present on numerous
cell types. IL1 may activate adenylate cyclase, elevating
cAMP levels and then activating protein kinase A, or it may
induce nuclear factors that serve as cellular gene transcriptional
activators. IL1 may induce synthesis of enzymes
that generate prostaglandins, which may in turn induce
fever, a well known action of IL1. The actions of IL1 differ
according to whether it is produced in lower or higher concentrations.
At low concentrations, the effects are mainly
immunoregulatory. IL1 acts with polyclonal activators to
facilitate CD4 + T lymphocyte proliferation and B lymphocyte
growth and differentiation. It stimulates multiple
cells to act as immune or inflammatory response effector
cells. It also induces further synthesis of itself and of IL6
by mononuclear phagocytes and vascular endothelium. It
resembles TNF in inflammatory properties. IL1 secreted
in greater amounts produces endocrine effects as it courses
through the peripheral blood circulation. For example, it
produces fever and promotes the formation of acute phase
plasma proteins in the liver. It also induces cachexia.
Natural inhibitors of IL1 may be produced by mononuclear
phagocytes activated by immune complexes in humans. The
inhibitor is biologically inactive and prevents the action of
IL1 by binding with its receptor, serving as a competitive
inhibitor. Corticosteroids and prostaglandins suppress IL1
secretion. IL1 was formerly called lymphocyte-activating
factor (LAF).
interleukin-1 receptor (IL1R)
An 80-kDa receptor found on T lymphocytes, chondrocytes,
osteoblasts, and fibroblasts that binds IL1α and
IL1β. Helper/inducer CD4 + T lymphocytes are richer in
IL1R than suppressor/cytotoxic (CD8 + ) T cells. IL1R has