The principal anti-inflammatory cytokines and cytokine inhibitors are listed in Tables 1, 2. The functional definition of an anti-inflammatory cytokine is the ability of the cytokine to inhibit the synthesis of IL-1, tumor necrosis factor (TNF), and other major proinflammatory cytokines.
Table 1: Cytokines with anti-inflammatory activities
|Il-1ra||Specific inhibitor of IL-1α and IL-1β mediated cellular activation at the IL-1 cellular receptor level|
|IL-4||Promotes Th2 lymphocyte development; inhibition of LPS-induced proinflammatory cytokines synthesis|
|IL-6||Inhibition of TNF and IL-1 production by macrophages|
|IL-10||Inhibition of monocyte/macrophage and mrutrophil cytokine production and inhibition of TH1-type lymphocyte responses|
|IL-11||Inhibits proinflammatory cytokines response by monocyte/macrophages and promotes Th2 lymphocyte response|
|IL-13||Shares homology with IL-4 and shares IL-4 receptor; attenuation of monocyte/macrophage function|
|TGF-β||Inhibition of monocyte/macrophage MHC, class II expression and proinflammatory cytokines synthesis|
Table 2: Soluble Cytokin Receptors With Anti-inflammatory Activities
|Solube receptor||Major Activities|
|Solube TNF receptor p55 (sTNFRI or sTNFRp55)||Binds to TNF trimers in the circulation, preventing membrane-bound TNF receptor-TNF ligand interactions|
|Solube TNF receptor p75(sTNFRII or sTNFRP75)||Binds to TNF trimers in the circulation, preventing membrane-bound TNF receptor-TNF ligand interactions|
|Soluble IL-1 receptor type 2 (sIL-1RII)||Binds to circulating IL-1 ligands in the plasma, preventing IL-1β from binding to the IL-1 receptor type 1|
|Membrane-bound IL-1 receptor type 2 (mIL-1RII)||Decoy receptor that lacks intracellular signaling function and competes with type 1 IL-1R for IL-1 ligand binding at the cell membrane|
|IL-18 binding protein (IL-18BP)||Solube extracellular domain of IL-18 receptor that function as a decoy receptor and binds circulating IL-18|
IL-1ra is a 152-amino-acid protein that functions as a specific inhibitor of the two other functional members of the IL-1 family, IL-1a and IL-1 b. IL-1ra blocks the action of IL-1a and IL-1b functional ligands by competitive inhibition at the IL-1 receptor level. IL-1ra binds with equal or greater affinity than does IL-1a and IL-1 b to the type 1 (80 kd) membrane-bound IL-1 receptor. IL-1ra does not bind with high affinity to the type II (68 kd) IL-1 receptor.
IL-1ra is produced by monocytes and macrophages and is released into the systemic circulation in >100-fold excess than either IL-1a or IL-1 b after lipopolysaccharide (LPS) stimulation in human volunteers. The synthesis of IL-1ra and IL-1 b are differentially regulated at their own promoter sites. Although bacterial LPS stimulates the synthesis of both IL-1b and IL-1ra, other stimuli cause differential release of IL-1ra and IL-1 b. The anti-inflammatory cytokines IL-4, IL-6, IL-10, and IL-13 inhibit the synthesis of IL-1 b, yet they stimulate the synthesis of IL-1ra.
Because IL-1 is such a prominent proinflammatory cytokine in a multitude of systemic inflammatory states, IL-1ra has been extensively studied in clinical trials as a specific IL-1 inhibitor. Despite convincing evidence that IL-1 plays an important role in the pathogenesis of bacterial sepsis, the results of IL-1ra therapy in large phase III clinical trials for severe sepsis have been disappointing. Nonetheless, IL-1ra continues to be a promising new treatment for the management of patients with refractory forms of rheumatoid arthritis.
IL-4 is a highly pleiotropic cytokine that is able to influence Th cell differentiation. Early secretion of IL-4 leads to polarization of Th cell differentiation toward Th2-like cells. Th2-type cells secrete their own IL-4, and subsequent autocrine production of IL-4 supports cell proliferation. The Th2- cell secre-infections is not adequately defined and will necessitate additional clinical investigation. IL-4 is able to affect a variety of structural cells. It can potentiate proliferation of vascular endothelium and skin fibroblasts yet decrease proliferation of adult human astrocytes and vascular smooth muscle cells. In addition, IL-4 induces a potent cytotoxic response against tumors. In a study of 63 patients with stage IV non-small cell lung cancer, data on treatment with recombinant human IL-4 seemed to suggest a possible dose-related response. IL-4 may act by stabilizing disease and modifying tumor growth rates in addition to inducing tumor shrinkage and cell death without causing severe side effects, suggesting a possible adjuvant role for IL-4 in the treatment of malignant diseases.
IL-6 has long been regarded as a proinflammatory cytokine induced by LPS along with TNF-a and IL-1. IL-6 is often used as a marker for systemic activation of proinflammatory cytokines. Like many other cytokines, IL-6 has both proinflammatory and anti-inflammatory properties. Although IL-6 is a potent inducer of the acute-phase protein response, it has anti-inflammatory properties as well. IL-6, like other members of the gp130 receptor ligand family, acts predominantly as an anti-inflammatory cytokine. IL-6 down-regulates the synthe-sis of IL-1 and TNF.
IL-6 attenuates the synthesis of the proinflammatory cytokines while having little effect on the synthesis of anti-inflammatory cytokines such as IL-10 and transforming growth factor- b (TGF- b). IL-6 induces the synthesis of glucocorticoids and promotes the synthesis of IL-1ra and soluble TNF receptor release in human volunteers. At the same time, IL-6 inhibits the production of proinflammatory cytokines such as GM-CSF, IFN- g, and MIP-2. The net result of these immunologic effects place IL-6 the anti-inflammatory cytokine group.
IL-10 is the most important anti-inflammatory cytokine found within the human immune response. It is a potent inhibitor of Th1 cytokines, including both IL-2 and IFN- g. This activity accounts for its initial designation as cytokine synthesis inhibition factor. In addition to its activity as a Th2 lymphocyte cytokine, IL-10 is also a potent deactivator of monocyte/macrophage proinflammatory cytokine synthesis. After engaging its high-affinity 110-kd cellular receptor, IL-10 inhibits monocyte/macrophage-derived TNF-a, IL-1, IL-6, IL-8, IL-12, granulocyte colony-stimulating factor, MIP-1 a, and MIP-2a.
IL-11 has been shown to attenuate IL-1 and TNF synthesis from macrophages by up-regulating inhibitory NF-kB (in-hibitory NF-kB) synthesis in monocyte/macrophage cell lines. Inhibitory NF- kB prevents NF- kB from translocating to the nucleus where NF- kB functions as a transcriptional activator for the proinflammatory cytokines. IL-11 has also been shown to inhibit the synthesis of IFN-g and IL-2 by CD41 T cells. IL-11 functions as a Th2-type cytokine, with induction of IL-4 and Inhibition of Th1-type cytokines. IL-11 does not induce the synthesis of IL-10 or TGF- b. This indicates that IL-11 is a direct inhibitor of Th1 lymphocytes and does not act indirectly through induction of IL-10.
IL-13 and IL-4 share a common cellular receptor (IL-4 type 1 receptor), and this accounts for many of the similarities between these two anti-inflammatory cytokines. IL-4 and IL-13 share only 20% to 25% primary amino acid homology, but the majora-helical regions that are essential for their activity are highly homologous. IL-13 can down-regulate the production of TNF, IL-1, IL-8, and MIP-1α by monocytes and has profound effects on expression of surface molecules on both monocytes and macrophages.
Like many cytokines, TGF-β has both pro- and anti-inflammatory effects. It functions as a biological switch, antagonizing or modifying the action of other cytokines or growth factors. The presence of other cytokines may modulate the cellular response to TGF-β, and the effect may differ depending on the activation state of the cell. TGF-β is capable of converting an active site of inflammation into one dominated by resolution and repair. TGF-b often exhibits disparate effects with immune-enhancing activity in local tissues and immune-suppressive activity in the systemic circulation. TGF-β1 suppresses the proliferation and differentiation of T cells and B cells and limits IL-2, IFN- g, and TNF production. TGF-β1 acts as a monocyte/macrophage deactivator in a manner similar to IL-10. However, TGF-βis less potent an inhibitor than IL-10 and has little or no effect on IL-1 production. The severe and uncontrolled inflammatory reactions observed in the TGF-β1 knockout mouse attests to the physiologic role of TGF-b as an endogenous anti-inflammatory cytokine.
There are also many soluble cytokine receptors as anti-inflammatory molecules. Such as: type 1 (p55) and type 2 (p75) receptors for human TNF-α.
1, Milligan ED, Sloane EM, Langer SJ, et al. Controlling neuropathic pain by adeno-associated virus
driven production of the anti-inflammatory cytokine, interleukin-10. Mol Pain 2005;1:9. [PubMed:
2, Uceyler N, Valenza R, Stock M, et al. Reduced levels of anti-inflammatory cytokines in patients with chronic widespread pain. Arthritis Rheum 2006;54:2656–2664. [PubMed: 16871547]
3, Wieseler-Frank J, Maier SF, Watkins LR. Glial activation and pathological pain. Neurochem Int 2004;45:389–395. [PubMed: 15145553]
4, Heijmans-Antonissen C, Wesseldijk F, Munnikes RJ, et al. Multiplex bead array assay for detection of 25 soluble cytokines in blister fluid of patients with complex regional pain syndrome type 1.Mediators Inflamm 2006;2006:28398. [PubMed: 16864900]
5, Roberts AB, Sporn MB. Physiological actions and clinical applications of transforming growth factor- beta (TGF-beta). Growth Factors 1993;8:1–9. [PubMed: 8448037]