Inflammatory cytokine

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An inflammatory cytokine or proinflammatory cytokine is a type of signaling molecule (a cytokine) that is secreted from immune cells like helper T cells (Th) and macrophages, and certain other cell types that promote inflammation. They include interleukin-1 (IL-1), IL-6, IL-12, and IL-18, tumor necrosis factor alpha (TNF-α), interferon gamma (IFNγ), and granulocyte-macrophage colony stimulating factor (GM-CSF) and play an important role in mediating the innate immune response. Inflammatory cytokines are predominantly produced by and involved in the upregulation of inflammatory reactions.

Contents

Excessive chronic production of inflammatory cytokines contribute to inflammatory diseases, that have been linked to different diseases, such as atherosclerosis and cancer. Dysregulation has also been linked to depression and other neurological diseases. A balance between proinflammatory and anti-inflammatory cytokines is necessary to maintain health. Aging and exercise also play a role in the amount of inflammation from the release of proinflammatory cytokines.

Therapies to treat inflammatory diseases include monoclonal antibodies that either neutralize inflammatory cytokines or their receptors.

Definition

An inflammatory cytokine is a type of cytokine (a signaling molecule) that is secreted from immune cells and certain other cell types that promotes inflammation. Inflammatory cytokines are predominantly produced by T helper cells (Th) and macrophages and involved in the upregulation of inflammatory reactions. [1] Therapies to treat inflammatory diseases include monoclonal antibodies that either neutralize inflammatory cytokines or their receptors. [2]

Inflammatory cytokines include interleukin-1 (IL-1), IL-12, and IL-18, tumor necrosis factor alpha (TNF-α), interferon gamma (IFNγ), and granulocyte-macrophage colony stimulating factor (GM-CSF). [3]

Function

Inflammatory cytokines play a role in initiating the inflammatory response and to regulate the host defence against pathogens mediating the innate immune response. [4] Some inflammatory cytokines have additional roles such as acting as growth factors. [5] Pro-inflammatory cytokines such as IL-1β, IL-6, and TNF-α also trigger pathological pain. [1] While IL-1β is released by monocytes and macrophages, it is also present in nociceptive DRG neurons. IL-6 plays a role in neuronal reaction to an injury. TNF-α is a well known proinflammatory cytokine present in neurons and the glia. TNF-α is often involved in different signaling pathways to regulate apoptosis in the cells.[ citation needed ] Excessive chronic production of inflammatory cytokines contribute to inflammatory diseases. [2] that have been linked to different diseases, such as atherosclerosis and cancer. Dysregulation of proinflammatory cytokines have also been linked to depression and other neurological diseases. A balance between proinflammatory and anti-inflammatory cytokines is necessary to maintain health. Aging and exercise also play a role in the amount of inflammation from the release of proinflammatory cytokines. [6]

Negative impacts

Due to its proinflammatory action, a proinflammatory cytokine tends to make the disease itself or the symptoms correlated to a disease worse by causing fever, inflammation, tissue destruction, and in some cases, even shock and death. [7] Excessive amounts of proinflammatory cytokines have been shown to cause detrimental effects [2]

In the kidney

A proinflammatory cytokine affects functions of transporters and ion channels from the nephron. As a result, there is a change in the activity of the potassium ion (K+) channels that changes the transepithelial transport of solutes and water in the kidney. [8] The kidney proximal tubule cells produce proinflammatory cytokines in response to lipopolysaccharide. Proinflammatory cytokines affect the renal K+ channels. IFNγ causes delayed suppression and acute stimulation of the 40 pS K+ channel. Also, transforming growth factor beta 1 (TGF-β1) activates the calcium-activated potassium channel (KCa3.1) which could be involved the detrimental effects of renal fibrosis.[ citation needed ]

Graft-vs-host disease

Graft-versus-host disease (GvHD) targets JAK 1 and 2, the human tyrosine kinase protein required for signaling in multiple cytokines. When these kinases are activated, signal proteins of the signal transducer and activator of transcription (STAT) protein family – which include transcription factors for target genes that serve proinflammatory roles – are phosphorylated. [9] The severity of GvHD is highly variable and is influenced by the amount of native cells present in the environment along with other regulatory T cells, TH1, TH2, or TH17 phenotypes. [10] Both CD4+ and CD8 IL-17 producing T cells have been shown to cause aTH1, causing tissue inflammation and resulting in severe GVHD. [11]

In cystic fibrosis

A proinflammatory cytokine causes hyperinflammation, the leading cause of lung tissue destruction in cystic fibrosis. [12] With such a strong inflammatory response and an elevated number of immune cells, lungs of cystic fibrosis patients cannot clear the bacteria and become more susceptible to infections. A high prevalence (40-70%) of patients with cystic fibrosis show signs of asthma, possibly due to the primary deficiency in the cystic fibrosis transmembrane conductance regulator (CFTR). [13] CFTR-deficient T-helper cells create an inflammatory environment that has high concentrations of TNF-α, IL-8, and IL-13, which contributes to increased contractility of airway smooth muscle.[ citation needed ]

In cardiovascular disease

Atherosclerosis induces a dysfunctional endothelium, which recruits immune cells that form lesions. Proinflammatory mediators cause inflammation after ligands in the heart vasculature activate immune cells. [14] Recent studies have shown the ability of exercise to control oxidative stress and inflammation in cardiovascular disease.[ citation needed ]

In adipose tissue metabolism and obesity

A proinflammatory cytokine may be present in adipose tissues. Adipocytes generate TNF-α and other interleukins. Cytokines derived from adipose tissue serve as remote regulators such as hormones. Studies have shown that TNF-α and IL-6 concentrations are elevated in obesity. [15] [16] [17] Obesity leaves an excess of nutrients for the body, thereby causing adipocytes to release more proinflammatory cytokines. Classically activated macrophages in the visceral fat accumulate in the fat tissues and continuously release proinflammatory cytokines, causing chronic inflammation in obese individuals.[ citation needed ]

In osteoarthritis

TNF-α, IL-1 and IL-6 have been found to play a pivotal role in cartilage matrix degradation and bone resorption in osteoarthritis. [18] Animal studies indicate that inflammatory cytokines may stimulate chondrocytes to release cartilage-degrading protease in osteoarthritis. This finding does not, however, necessarily translate to Homo sapiens , as osteoarthritis in humans is considered to be more complex than any animal model. [19]

Fatigue

Cytokines have key roles in inflammation, which is seen as a causal mechanism in fatigue. [20] [21]

Clinical implications

Reducing the biological activity of proinflammatory cytokine can reduce the brunt of attack from diseases. [7]

Blocking IL-1 or TNF-α has been highly successful in helping patients with rheumatoid arthritis, inflammatory bowel disease, [22] or graft-vs-host disease (GvHD). [7] However, the strategy has not yet been successful in humans with sepsis. [7] Therapeutic effects of acupuncture may be related to the body's ability to suppress a range of proinflammatory cytokines such as tumor necrosis factor alpha (TNF-α), IL-1B, IL-6, and IL-10. [23]

Estrogen has been shown to promote healing by decrease the production of various proinflammatory cytokines like IL-6, [24] TNF-α, [25] and macrophage migration inhibitory factor (MIF). Increased MIF levels are often found at the site of chronic non-healing ulcers, with those levels dropping significantly with successful healing. A 2005 review of current experimental data shows that "estrogen regulates healing almost exclusively via MIF down-regulation and identifies novel MIF-regulated gene targets and clusters associated with aberrant healing." By down-regulating MIF, estrogen can promote healing, as correlated by clinical studies on aging skin and skin wounds. Unfortunately, estrogen-therapy has known carcinogenic effects [26] as mentioned by the American Cancer Society (increased incidences of breast cancer in women who undergo HRT). However, scientists could make important discoveries in the future by studying "downstream effects on genes/factors that mediate the effects of estrogen on healing." [27]

Histone deacetylate inhibitors (HDACi) can suppress proinflammatory cytokine production and reduce GvHD.[ citation needed ]

Some research also suggest an immunoregulatory effect of vitamin D, which has been shown to reduce the secretion of specific inflammatory cytokines. [28] [29]

Related Research Articles

<span class="mw-page-title-main">Inflammation</span> Physical effects resulting from activation of the immune system

Inflammation is part of the biological response of body tissues to harmful stimuli, such as pathogens, damaged cells, or irritants. The five cardinal signs are heat, pain, redness, swelling, and loss of function.

<span class="mw-page-title-main">Cytokine</span> Broad and loose category of small proteins important in cell signaling

Cytokines are a broad and loose category of small proteins important in cell signaling. Due to their size, cytokines cannot cross the lipid bilayer of cells to enter the cytoplasm and therefore typically exert their functions by interacting with specific cytokine receptors on the target cell surface. Cytokines have been shown to be involved in autocrine, paracrine and endocrine signaling as immunomodulating agents.

<span class="mw-page-title-main">Macrophage</span> Type of white blood cell

Macrophages are a type of white blood cell of the innate immune system that engulf and digest pathogens, such as cancer cells, microbes, cellular debris, and foreign substances, which do not have proteins that are specific to healthy body cells on their surface. This process is called phagocytosis, which acts to defend the host against infection and injury.

<span class="mw-page-title-main">Tumor necrosis factor</span> Protein

Tumor necrosis factor is an adipokine and a cytokine. TNF is a member of the TNF superfamily, which consists of various transmembrane proteins with a homologous TNF domain.

<span class="mw-page-title-main">Resistin</span> Mammalian protein found in Homo sapiens

Resistin also known as adipose tissue-specific secretory factor (ADSF) or C/EBP-epsilon-regulated myeloid-specific secreted cysteine-rich protein (XCP1) is a cysteine-rich peptide hormone derived from adipose tissue that in humans is encoded by the RETN gene.

Stromal cells, or mesenchymal stromal cells, are differentiating cells found in abundance within bone marrow but can also be seen all around the body. Stromal cells can become connective tissue cells of any organ, for example in the uterine mucosa (endometrium), prostate, bone marrow, lymph node and the ovary. They are cells that support the function of the parenchymal cells of that organ. The most common stromal cells include fibroblasts and pericytes. The term stromal comes from Latin stromat-, "bed covering", and Ancient Greek στρῶμα, strôma, "bed".

<span class="mw-page-title-main">Interleukin 8</span> Mammalian protein found in Homo sapiens

Interleukin 8 is a chemokine produced by macrophages and other cell types such as epithelial cells, airway smooth muscle cells and endothelial cells. Endothelial cells store IL-8 in their storage vesicles, the Weibel-Palade bodies. In humans, the interleukin-8 protein is encoded by the CXCL8 gene. IL-8 is initially produced as a precursor peptide of 99 amino acids which then undergoes cleavage to create several active IL-8 isoforms. In culture, a 72 amino acid peptide is the major form secreted by macrophages.

Lymphotoxin is a member of the tumor necrosis factor (TNF) superfamily of cytokines, whose members are responsible for regulating the growth and function of lymphocytes and are expressed by a wide variety of cells in the body.

<span class="mw-page-title-main">Interleukin 32</span> Protein-coding gene in the species Homo sapiens

Interleukin 32 (IL32) is proinflammatory cytokine that in humans is encoded by the IL32 gene. Interleukin 32 can be found in higher mammals but not in rodents. It is mainly expressed intracellularly and the protein has nine different isoforms, because the pre-mRNA can be alternatively spliced. The most active and studied isoform is IL-32γ. It was first reported in 2005, although the IL-32 gene was first described in 1992. It does not belong to any cytokine family because there is almost no homology with other cytokines.

<span class="mw-page-title-main">Interleukin 19</span> Protein-coding gene in the species Homo sapiens

Interleukin 19 (IL-19) is an immunosuppressive protein that belongs to the IL-10 cytokine subfamily.

<span class="mw-page-title-main">Alveolar macrophage</span>

An alveolar macrophage, pulmonary macrophage, is a type of macrophage, a professional phagocyte, found in the airways and at the level of the alveoli in the lungs, but separated from their walls.

<span class="mw-page-title-main">Macrophage migration inhibitory factor</span> Protein-coding gene in the species Homo sapiens

Macrophage migration inhibitory factor (MIF), also known as glycosylation-inhibiting factor (GIF), L-dopachrome isomerase, or phenylpyruvate tautomerase is a protein that in humans is encoded by the MIF gene. MIF is an important regulator of innate immunity. The MIF protein superfamily also includes a second member with functionally related properties, the D-dopachrome tautomerase (D-DT). CD74 is a surface receptor for MIF.

Adipose tissue macrophages (ATMs) comprise tissue resident macrophages present in adipose tissue. Adipose tissue apart from adipocytes is composed of the stromal vascular fraction (SVF) of cells including preadipocytes, fibroblasts, vascular endothelial cells and variety of immune cells. The latter ones are composed of mast cells, eosinophils, B cells, T cells and macrophages. The number of macrophages within adipose tissue differs depending on the metabolic status. As discovered by Rudolph Leibel and Anthony Ferrante et al. in 2003 at Columbia University, the percentage of macrophages within adipose tissue ranges from 10% in lean mice and humans up to 50% in extremely obese, leptin deficient mice and almost 40% in obese humans. Increased number of adipose tissue macrophages correlates with increased adipose tissue production of proinflammatory molecules and might therefore contribute to the pathophysiological consequences of obesity.

Innate lymphoid cells (ILCs) are the most recently discovered family of innate immune cells, derived from common lymphoid progenitors (CLPs). In response to pathogenic tissue damage, ILCs contribute to immunity via the secretion of signalling molecules, and the regulation of both innate and adaptive immune cells. ILCs are primarily tissue resident cells, found in both lymphoid, and non- lymphoid tissues, and rarely in the blood. They are particularly abundant at mucosal surfaces, playing a key role in mucosal immunity and homeostasis. Characteristics allowing their differentiation from other immune cells include the regular lymphoid morphology, absence of rearranged antigen receptors found on T cells and B cells, and phenotypic markers usually present on myeloid or dendritic cells.

Neuroinflammation is inflammation of the nervous tissue. It may be initiated in response to a variety of cues, including infection, traumatic brain injury, toxic metabolites, or autoimmunity. In the central nervous system (CNS), including the brain and spinal cord, microglia are the resident innate immune cells that are activated in response to these cues. The CNS is typically an immunologically privileged site because peripheral immune cells are generally blocked by the blood–brain barrier (BBB), a specialized structure composed of astrocytes and endothelial cells. However, circulating peripheral immune cells may surpass a compromised BBB and encounter neurons and glial cells expressing major histocompatibility complex molecules, perpetuating the immune response. Although the response is initiated to protect the central nervous system from the infectious agent, the effect may be toxic and widespread inflammation as well as further migration of leukocytes through the blood–brain barrier may occur.

Macrophage polarization is a process by which macrophages adopt different functional programs in response to the signals from their microenvironment. This ability is connected to their multiple roles in the organism: they are powerful effector cells of the innate immune system, but also important in removal of cellular debris, embryonic development and tissue repair.

Microglia are the primary immune cells of the central nervous system, similar to peripheral macrophages. They respond to pathogens and injury by changing morphology and migrating to the site of infection/injury, where they destroy pathogens and remove damaged cells.

Otilimab is a fully human antibody which has been developed by the biotechnology company MorphoSys. It can also be referred to as HuCAL antibody, HuCAL standing for Human Combinatorial Antibody Library and being a technology used to generate monoclonal antibodies. Otilimab is directed against the granulocyte-macrophage colony stimulating factor (GM-CSF), a monomeric glycoprotein functioning as a cytokine promoting both proliferation and activation of macrophages and neutrophils.

<span class="mw-page-title-main">Dermal macrophage</span> Skin macrophages used for wound repair and hair growth

Dermal macrophages are macrophages in the skin that facilitate skin homeostasis by mediating wound repair, hair growth, and salt balance. Their functional role in these processes is the mediator of inflammation. They can acquire an M1 or M2 phenotype to promote or suppress an inflammatory response, thereby influencing other cells' activity via the production of pro-inflammatory or anti-inflammatory cytokines. Dermal macrophages' ability to acquire pro-inflammatory properties also potentiates them in cancer defence. M1 macrophages can suppress tumour growth in the skin by their pro-inflammatory properties. However, M2 macrophages support tumour growth and invasion by the production of Th2 cytokines such as TGFβ and IL-10. Thus, the exact contribution of each phenotype to cancer defence and the skin's homeostasis is still unclear.

Immune system contribution to regeneration of tissues generally involves specific cellular components, transcription of a wide variety of genes, morphogenesis, epithelia renewal and proliferation of damaged cell types. However, current knowledge reveals more and more studies about immune system influence that cannot be omitted. As the immune system exhibits inhibitory or inflammatory functions during regeneration, the therapies are focused on either stopping these processes or control the immune cells setting in a regenerative way, suggesting that interplay between damaged tissue and immune system response must be well-balanced. Recent studies provide evidence that immune components are required not only after body injury but also in homeostasis or senescent cells replacement.

References

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  21. ↑
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