Cytokines & Chemokines

Interleukin-16 (IL-16) is a CD8+ T cell-derived cytokine that induces chemotaxis of CD4+ T cells and CD4+ monocytes and eosinophils. Analysis by gel filtration suggests that, under physiological conditions, human IL-16 exists predominantly as a noncovalently linked multimer, but that some IL-16 may exist as a monomer. However, only the multimeric form appears to possess chemotactic activity, suggesting that receptor cross-linking may be required for activity. IL-16 also induces expression of IL-2 receptor (IL-2R) and MHC class II molecules on CD4+ T cells. Human and murine IL-16 show significant cross-species reactivity.

Interleukin-17 is a potent pro-inflammatory cytokine produced by activated memory T cells. There are at least six members of the IL-17 family in humans and in mice. As IL-17 shares properties with IL-1 and TNF-alpha; it may induce joint inflammation and bone and cartilage destruction. This cytokine is found in synovial fluids of patients with rheumatoid arthritis; and produced by rheumatoid arthritis synovium. It increases IL-6 production; induces collagen degradation and decreases collagen synthesis by synovium and cartilage and proteoglycan synthesis in cartilage. IL-17 is also able to increase bone destruction and reduce its formation. Blocking of interleukin-17 with specific inhibitors provides a protective inhibition of cartilage and bone degradation.

Interleukin-18 is a secreted protein and it belongs to the IL-1 family. IL-18 is a proinflammatory cytokine and produced by macrophages and other cells. This cytokine can induce the IFN-gamma production of T cells. The combination of this cytokine and IL12 has been shown to inhibit IL-4 dependent IgE and IgG1 production; and enhance IgG2a production of B cells. IL-18 binding protein (IL18BP) can specifically interact with this cytokine; and thus negatively regulate its biological activity. After stimulation with IL-18; natural killer (NK) cells and certain T cells release another important cytokine called interferon-γ (IFN-γ) or type II interferon that plays an important role in activating the macrophages or other cells.

Human Interleukin 31 (IL-31) is a cytokine containing a four-helix bundle structure. It shares several structural and functional characteristics with IL-6, Oncostatin M, LIF, and Cardiotrophin-1. Human IL-31 cDNA encodes a 164 amino acid precursor that contains a 23 amino acid signal peptide and a 141 amino acid mature protein. Human and mouse IL-31 share 24% sequence identity in the mature region. IL-31 is mainly associated with activated T cells and is preferentially expressed by type 2 helper T cells (Th2). IL-31 signals via a heterodimeric receptor complex composed of a gp130 related molecule termed IL-31RA (also GPL and GLMR) and an Oncostatin M receptor (OSM Rβ). The IL-31 receptor is constitutively expressed by keratinocytes and upregulated by IFNγ on monocytes. GPL/OSMR signaling is a strong activator of STAT3 and STAT5, and can also activate STAT1, Jak1, and Jak2 signaling pathways. IL-31 regulated immune responses have been implicated in skin physiology and inflammatory skin

Interleukin-4 (IL-4) is a pleiotropic cytokine that regulates diverse T and B cell responses including cell proliferation; survival and gene expression. IL-4 is produced by mast cells; T cells; and bone marrow stromal cells. IL-4 regulates the differentiation of naive CD4+ T cells into helper Th2 cells; characterized by their cytokine-secretion profile that includes secretion of IL-4; IL-5; IL-6; IL-10; and IL-13; which favor a humoral immune response. Another dominant function of IL-4 is the regulation of immunoglobulin class switching to the IgG1 and IgE isotypes. Excessive IL-4 production by Th2 cells has been associated with elevated IgE production and allergic response.

Interleukin-33 (IL-33) was initially discovered as a nuclear factor NF-HEV abundantly expressed in high endothelial venules. It is a 30-32 kD pro-inflammatory protein with intracellular and extracellular activities and a chromatin-associated cytokine of the IL-1 family with high sequence and structural similarity to IL-1 and IL-18. IL-33 is highly and selectively expressed by high endothelial venule endothelial cells (HEVECs) in human tonsils; Peyers's patches; and lymph nodes. It contains a bipartite nuclear localization signal at the C-terminus; and is targeted to the nucleus when ectopically expressed in human umbilical vein endothelial cells (HUVECs) and HeLa cells. The C-terminal fragment; corresponding to mature IL-33; binds and triggers signaling. IL-33 mediates its biological effects via Toll-interleukin 1 (IL-1) receptor (TIR) domain-containing receptor ST2; activates NF-kappaB and MAP kinases; and drives production of T(H)2-associated cytokines from in vitro polarized T(H

Interleukin-18 is a secreted protein and it belongs to the IL-1 family. IL-18 is a proinflammatory cytokine and produced by macrophages and other cells. This cytokine can induce the IFN-gamma production of T cells. The combination of this cytokine and IL12 has been shown to inhibit IL-4 dependent IgE and IgG1 production; and enhance IgG2a production of B cells. IL-18 binding protein (IL18BP) can specifically interact with this cytokine; and thus negatively regulate its biological activity. After stimulation with IL-18; natural killer (NK) cells and certain T cells release another important cytokine called interferon-γ (IFN-γ) or type II interferon that plays an important role in activating the macrophages or other cells.

IL-5 is expressed in eosinophils, NK cells, TC2 CD8+ T cells, mast cells, CD45+ CD4+ T cells, gamma delta T cells and IL-1 beta activated endothelial cells. IL-5 acts as a growth and differentiation factor for both B cells and eosinophils. Relative to B cells, IL-5 appears to induce the differentiation of activated conventional B-2 cells into Ig-secreting cells. In addition, it induces the growth of B-1 progenitors as well as IgM production by B-1 cells.IL-5 appears to perform a number of functions on eosinophils. These include the down modulation of Mac-1,the upregulation of receptors for IgA and IgG,the stimulation of lipid mediator (leukotriene C4 and PAF) secretion and the induction of granule release.IL-5 also promotes the growth and differentiation of eosinophils.

Interleukin-13 is also known as IL-13. It is a protein that in humans is encoded by the IL13 gene. Interleukin-13 is an immunoregulatory cytokine produced primarily by activated Th2 cells.It is involved in several stages of B-cell maturation and differentiation. It up-regulates CD23 and MHC class II expression, and promotes IgE isotype switching of B cells. This cytokine down-regulates macrophage activity, thereby inhibits the production of pro-inflammatory cytokines and chemokines. This cytokine is found to be critical to the pathogenesis of allergen-induced asthma but operates through mechanisms independent of IgE and eosinophils.