Cytokines: Interleukins
125
I
L
-
1
01
7
81
6
0N
o
t
g
l
y
c
o
s
y
l
a
t
e
d
b
u
t
contains one site
of N-linked
glycosylation
2
(5-cysteines)
D
1 (5/4)
110 kDa binding protein
IL-11
199
178
0
(2-cysteines)
M1
9
1
5
0
k
D
a
α
-chain
130 kDa ß-chain - (gp130)
IL-12
Two similar chains
p35
253
197
N-linked
3
(7-cysteines)
D (Heterodimer)
3
5
related to gp130 named IL-12R
β
1
&IL-12R
β
2
p40
326
306
N-linked
5
IL-13
132
112
N-linked
2
M
5
Two IL-13R
α
chains (HR family)
in combination with
components shared with IL-4
IL-14
498
483
N-linked
?
M
IL-15
162
114
N-linked
2
M
4
SpeciFc IL-15R
α
chain, with
IL-2R
β
&IL-2R
γ
shared with
IL-2
A growing number of additional interleukins have now been characterized; however, by and large, these belong to the previously characterized interleukin
families. ±or instance, several IL-1 homologs have been identiFed, the genes of which are all on chromosome 2 close to IL-1
α
,IL-1
β
, and IL-1ra genes; in
contrast, the gene for IL-18, an IL-1 paralog, is located on chromosome 11. Genes for IL-10 paralogs IL-19, IL-20, and IL-24 are located at chromosome
1q32 along with the IL-10 gene, while those for IL-22 and IL-26 are located on chromosome 12q15, close to the I±N
γ
gene. IL-10 and related paralogs are
all V-shaped homodimers with topology resembling that of I±N
γ
. Receptors for IL-10 family members are constituted by speciFc pairs of class II cytokine
receptor chains. IL-28 and IL-29 are related to both IL-10 and type I I±N families; however, their genes resemble the intron–exon structure of IL-10-type
genes rather than the intronless type I I±N genes and are located on chromosome 19q13, away from either IL-10- and paralog genes, located as above, or
type I I±N genes on chromosome 9. The receptor for IL-28/29 is a distinct class II cytokine receptor pair composed of IL-10R
β
and CR±2-12 and different
from type I I±N receptors. IL-21 is a 4-helix cytokine most closely to IL-15; IL-23 and IL-27 are heterodimers structurally related to IL-12, IL-23 sharing with
IL-12 its p40 subunit and thus one of its receptors, IL-12R
β
1.
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