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Fig. 1
The paradigm of classic- and trans-signaling of IL-6. IL-6 binds to the mem-
brane bound IL-6R, induces dimerization of gp130 and signaling (
left
). On cells not
expressing IL-6R, IL-6 can only act by binding to the sIL-6R. The complex of IL-6
and sIL-6R can bind to gp130 and induce dimerization and signaling (
right
). By this
trans-signaling pathway virtually every cell in the body can respond to IL-6
(IL-11), Leukemia Inhibitory Factor (LIF), Ciliary Neurotrophic
Factor (CNTF), Cardiotrophin-1 (CT-1), Cardiotrophin-like
Cytokine (CLC), Oncostatin M (OSM), and Interleukin-27 (IL-
27) (
7, 8
). These cytokines comprise the gp130 family of cytokines
(
8, 9
). Signaling of cytokines of the gp130 family is similar, but not
identical since the receptor complexes for LIF, CNTF, CT-1, CLC,
OSM, and IL-27 consist of heterodimeric complexes of gp130 and
LIF-R, OSM-R, or WSX-1 (
5, 6
).
Interestingly, gp130 is expressed on all cells of the body
whereas IL-6R is only found in some cells (
7
). Since neither IL-6
nor IL-6R alone have a measurable affinity for gp130, it follows
that cells, which do not express IL-6R cannot respond to the
cytokine IL-6 (
10
). Cells, which do not express IL-6R include
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