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interleukin-2 receptor α subunit (IL2Rα) 401 interleukin-4 (IL4; B cell growth factor)
required for stimulation are effective when both receptors
are present on cell surfaces. Antibodies against p55 or p70
can block IL2 binding. Powerful antigenic stimulation such
as in transplant rejection may lead to the shedding of p55
IL2 receptors into the serum. The gene encoding the p55
chain is located on chromosome 10p14 in humans. IL2, IL1,
IL6, IL4, and TNF may induce IL2R expression.
interleukin-2 receptor subunit (IL2R)
The 55-kDa polypeptide subunit of IL2R with a K d of 10 –8
M. The α subunit is responsible for increasing the affinity
between cytokine and receptor; however, it has no role in
signal transduction. It is expressed only on antigen stimulation
of T cells, usually within 2 hours. Following long-term
T cell activation, the α subunit is shed, making it a potential
candidate as a serum marker of strong or prolonged antigen
stimulation. The gene encoding IL2Rα is located on chromosome
10p14 in humans.
α
1
cys 192
Interleukin-2.
β γ
1
: Cysteine
: Motif
WSXWS
Motif
251 Serine-rich
Region
Acidic
SH2
Homology
Subdomain
Region
347
Schematic representation of interleukin-2 receptor αβγ subunit (IR-2Rαβγ.)
525
interleukin-2 receptor subunit (IL2R)
The complete IL2 receptor consists of two distinct polypeptides:
IL2α, induced upon activation, and IL2βγ, present on
:
:
1
resting T cells. Upon expression of all three proteins, affinity
increases to 10 –11 M and very low (physiologic) levels
of IL2 are capable of stimulating cells. IL2R is found on T
lymphocytes, natural killer (NK) cells, and B lymphocytes,
although NK cells do not express IL2Rα. IL2, IL1, IL6,
IL4, and TNF may induce IL2R expression.
interleukin-2 receptor subunit (IL2R)
The 70- to 74-kDa subunit of IL2R with a K d of 10 –9 M.
The β subunit is a member of the cytokine receptor family
type I due to its tryptophan–serine–X–tryptophan–serine
(WSXWS) domain. It is a constitutive membrane protein
coordinately expressed with IL2Rγ.
interleukin-2 receptor subunit (IL2R)
A heterodimer found on resting T cells. Only T cells expressing
IL2R are capable of growth in response to IL2, as this is
the portion of the receptor responsible for signal transduction.
interleukin-2 receptor subunit (IL2R)
This subunit is also a type I (WSXWS) receptor associated
with IL4 and IL7 receptors as well as IL2Rγ. Mutations in the
γ subunit have been found in some cases of severe combined
immunodefiency syndrome (SCIDS) with X-linked inheritance,
resulting in decreased proliferation of B and T cells.
interleukin-3 (IL3)
A 20-kDa lymphokine synthesized by activated CD4 + T
helper lymphocytes that acts as a colony-stimulating factor
by facilitating proliferation of some hematopoietic cells and
promoting proliferation and differentiation of other lymphocytes.
It acts by binding to high and low affinity receptors,
inducing tyrosine phosphorylation and colony formation
of erythroid, myeloid, megakaryocytic, and lymphoid
hematopoietic cells. It also facilitates mast cell proliferation,
the release of histamine, and T lymphocyte maturation
through induction of 20α-hydroxysteroid dehydrogenase.
The gene encoding IL3 is situated on the long arm of chromosome
5. The IL3 gene in humans encodes a 152-amino
acid long protein, and the naturally occurring form of IL3
is glycosolated. IL3 facilitates natural immune defenses
against disease.
interleukin-3 receptor
A low-affinity IL3-binding α subunit (IL3α; CD123)
that associates with a β subunit to produce a high affinity
IL3 receptor. The IL3α subunit has an N terminal region
consisting of 100-amino acid residues, a cytokine receptor
domain, and a fibronectin III domain containing the
WSXWS motif. The truncated cytoplasmic domain is
associated with the inability to signal. The β subunit has
two homologous segments in the extracellular region. A
cytokine receptor domain followed by a fibronectin domain
is present in each segment. The human α chain contains six
potential N-linked glycosylation sites, whereas the β chain
has three. Tyrosine and serine/threonine phosphorylation of
numerous cellular proteins occurs rapidly following union
of IL3 with its receptor. The β subunit is requisite for signal
transduction.
interleukin-4 (IL4; B cell growth factor)
A 20-kDa cytokine that induces differentiation of naïve
helper T (Th0) cells to Th2 cells, subsets of CD4 + helper T
lymphocytes, that subsequently become the main producers
of the cytokine and may also be synthesized by activated
mast cells. Among its numerous biological functions are
the stimulation of activated B cell and T cell proliferation
and the differentiation of CD4 + T cells into Th2 cells. It is a
I