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interleukin-15 (IL15) 411 interleukin-17 (IL17)
IL14β. The il14 locus is situated near the gene for LCK on
chromosome 1 in humans.
interleukin-15 (IL15)
A T cell growth factor synthesized by mononuclear
phagocytes and other cells in response to viral infections.
It has many of the biological properties of IL2. Its principal
function is to stimulate the proliferation of natural
killer (NK) cells. IL15 enhances peripheral blood T cell
proliferation, and in vitro studies demonstrate its ability
to induce cytotoxic T cells. IL15 mRNA is expressed by
monocyte-enriched peripheral blood cell lines and placental
and skeletal muscle tissues. IL15 regulates T cell and NK
cell activation and proliferation. This cytokine shares many
biological activities with IL2. Both cytokines bind common
hematopoietin receptor subunits and may even compete for
the same receptor, and thus negatively regulate each other’s
activities. CD4 + memory cells are shown to be controlled by
a balance between this IL15 and IL2. IL15 induces activation
of JAKs as well as the phosphorylation and activation
of transcription factors STAT3, STAT5, and STAT6.
Murine studies suggest that IL15 may elevate expression
of apoptosis inhibitor BCL2L1/BCL-x(L), perhaps through
the transcription activation activity of STAT6, thereby
preventing apoptosis. IL15 may provide survival signals for
memory lymphocytes. NK cells fail to develop in transgenic
mice in which the IL15 receptor α (IL15Rα) gene has been
knocked out. Infectious mononucleosis infection appears
to be associated with the loss of IL15R expression by lymphocytes.
The IL2 and IL15 receptors also share a common
component for successful signal transduction. IL15 receptors
are widely expressed. IL15 plays a major role related to
NK cell development and cytolytic activity. The receptors
for IL15 on T cells contain IL2Rβ, γ c, one unique protein,
IL15Rα, and an alternate IL15 receptor designated IL15RX
and detected on mast cells. IL15 mediates its action by combination
with a heterotrimeric receptor composed of both β
and γ c chains of the IL2R as well as a unique IL15-binding
subunit known as IL15α. The IL15Rα chain is requisite
for high affinity binding but not signaling by IL15. IL2 and
IL15 have the same signaling pathways.
Interleukin-16.
interleukin-16 (IL16)
A 13.2-kDa protein containing 130-amino acid residues.
It is also called lymphocyte chemoattractant (LCA). It
activates a migratory response in CD4 + T cells and CD4 +
monocytes, eosinophils, and dendritic cells. Human IL16
also induces IL2 receptor expression by T lymphocytes.
IL16 has been found to suppress T cell proliferation and
mixed lymphocyte reactions. IL16 is structurally distinct
from chemokines and in the active form is a homotetramer
comprised of four 16-kDa chains. IL16 is produced as a
precursor peptide (pro-IL16) that requires processing by an
enzyme known as caspase-3 to become active. CD4 is the
cell signaling receptor for mature IL16. It is synthesized by
CD4 + T cells, mast cells, and eosinophils. Its gene is located
on human chromosome 15q26.1. CD4 may be a receptor
for IL16. IL16 is chemotactic for resting and activated T
cells, eosinophils, and monocytes. It facilitates CD4 + T cell
adhesion, expression of IL2Rα (CD25) and HLA-DR, and
cytokine synthesis. It suppresses antigen and alloantigen
(MLR)-induced lymphocyte proliferation. IL16 does not
competitively inhibit HIV–gp120 binding. It is a potent
survival factor and counters apoptotic effects of growthinducing
cytokines such as IL2. It has been found in bronchial
airway epithelial cells and fluids of asthmatics. It may
exacerbate allergic reactions. IL16 is a proinflammatory and
immunomodulatory cytokine.
Interleukin-17.
interleukin-17 (IL17)
IL17A belongs to the IL17 family of cytokines. Other family
members include IL17B, IL17C, IL17D, IL17E (IL25),
and IL17F. All members share similar protein structures
with four highly conserved cysteine residues relevant for
their three-dimensional shapes, although they exhibit no
sequence resemblance to other known cytokines. Amino
acids are 62 to 88% conserved between the human and
mouse homologs. The IL17 cytokine family has many
immune regulatory functions attributable to their induction
of numerous immune signaling molecules. IL17 participates
in the induction and mediation of proinflammatory
responses and is often associated with allergic phenomena.
It induces the synthesis of numerous other cytokines
including IL6, G-CSF, GM-CSF, IL1β, TGF-β, TNF-α and
chemokines including IL8, GRO-α, and MCP-1. It also
stimulates the synthesis of prostaglandins such as PGE 2
from numerous cell types such as fibroblasts, endothelial
cells, epithelial cells, keratinocytes, and macrophages.
A feature of IL17 cytokine-mediated responses includes
airway remodeling. Chemokine expression may attract
neutrophils. IL17 function is critical to the CD4 + T cell
subset called T helper 17 (Th17) cells. IL17 family members
have been associated with such immune or autoimmune
phenomena as asthma, lupus, allograft rejection and antitumor
immunity. The human IL17 gene cloned from CD4 + T
cells is 1874 base pairs in length. The IL17 family members
have a unique pattern of cellular expression. For example,
IL17A and IL17F are expressed by activated T cells that are
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