Interleukin 27 (IL-27) is a member of the IL-12 cytokine family. It is a heterodimeric cytokine that is encoded by two distinct genes, Epstein-Barr virus-induced gene 3 (EBI3) and IL-27p28. IL-27 is expressed by antigen presenting cells and interacts with a specific cell-surface receptor complex known as IL-27 receptor (IL-27R). [1] [2] [3] [4] [5] This receptor consists of two proteins, IL-27Rɑ and gp130. IL-27 induces differentiation of the diverse populations of T cells in the immune system and also upregulates IL-10.
When IL-27 binds to the IL-27 receptor, signaling pathways including JAK-STAT and p38 MAPK pathways are turned on. [6] [2] There are two types of responses, pro-inflammatory and anti-inflammatory, which involve different types of cells, such as macrophages, dendritic cells, T cells, and B cells. [3] The response that is activated is very much dependent on the external surrounding of IL-27. [1] [2] [3]
There are many different subsets of T cells, such as Th1, Th2, Th17, Tr1, and Treg cells; IL-27 is greatly involved in differentiation through inducing or suppressing of each T cell subset. [1] [2] [4] [5] Th1 cells, which express IFNγ, are generated by IL-27 through STAT1 dimerization and nuclear localization which subsequently leads to the expression of T-bet and signature Th1 genes. Th2 cells, which express IL-4, are inhibited by IL-27 through the transcription factor GATA-3. Th17 cells, which express IL-17, IL-22, and granulocyte macrophage colony-stimulating factor (GM-CSF), are inhibited by IL-27 through STAT1 and expression of transcription factor RORγt. Tr1 cells, which express IL-10, are induced by IL-27 through the transcription factor c-Maf. Treg cells are inhibited by IL-27 through STAT1 and STAT3. [2] [4] [5]
IL-10 acts in an anti-inflammatory manner by suppressing inflammatory responses. [7] One way that IL-27 can have an anti-inflammatory response is through the expression of IL-10. IL-27 has been found to be involved in the production of IL-10 by stimulating the various subsets of T cells, especially Tr1 cells. Also involved are the STAT1 and STAT3 transcription factors that bind specifically to the receptor subunits, IL-27ɑ and glycoprotein. IL-27 is able to activate STAT3 signaling, which eventually leads to an increase of IL-10 secretion from Treg cells. [1]
The T helper cells (Th cells), also known as CD4+ cells or CD4-positive cells, are a type of T cell that play an important role in the adaptive immune system. They aid the activity of other immune cells by releasing cytokines. They are considered essential in B cell antibody class switching, breaking cross-tolerance in dendritic cells, in the activation and growth of cytotoxic T cells, and in maximizing bactericidal activity of phagocytes such as macrophages and neutrophils. CD4+ cells are mature Th cells that express the surface protein CD4. Genetic variation in regulatory elements expressed by CD4+ cells determines susceptibility to a broad class of autoimmune diseases.
Cell-mediated immunity or cellular immunity is an immune response that does not involve antibodies. Rather, cell-mediated immunity is the activation of phagocytes, antigen-specific cytotoxic T-lymphocytes, and the release of various cytokines in response to an antigen.
Interleukin 12 (IL-12) is an interleukin that is naturally produced by dendritic cells, macrophages, neutrophils, and human B-lymphoblastoid cells (NC-37) in response to antigenic stimulation. IL-12 belongs to the family of interleukin-12. IL-12 family is unique in comprising the only heterodimeric cytokines, which includes IL-12, IL-23, IL-27 and IL-35. Despite sharing many structural features and molecular partners, they mediate surprisingly diverse functional effects.
The interleukin 4 is a cytokine that induces differentiation of naive helper T cells (Th0 cells) to Th2 cells. Upon activation by IL-4, Th2 cells subsequently produce additional IL-4 in a positive feedback loop. IL-4 is produced primarily by mast cells, Th2 cells, eosinophils and basophils. It is closely related and has functions similar to IL-13.
Nuclear factor of activated T-cells (NFAT) is a family of transcription factors shown to be important in immune response. One or more members of the NFAT family is expressed in most cells of the immune system. NFAT is also involved in the development of cardiac, skeletal muscle, and nervous systems. NFAT was first discovered as an activator for the transcription of IL-2 in T cells but has since been found to play an important role in regulating many more body systems. NFAT transcription factors are involved in many normal body processes as well as in development of several diseases, such as inflammatory bowel diseases and several types of cancer. NFAT is also being investigated as a drug target for several different disorders.
Interleukin 21 (IL-21) is a protein that in humans is encoded by the IL21 gene.
Interleukin-31 (IL-31) is a protein that in humans is encoded by the IL31 gene that resides on chromosome 12. IL-31 is an inflammatory cytokine that helps trigger cell-mediated immunity against pathogens. It has also been identified as a major player in a number of chronic inflammatory diseases, including atopic dermatitis.
Interleukin 30 (IL-30) forms one chain of the heterodimeric cytokine called interleukin 27 (IL-27), thus it is also called IL27-p28. IL-27 is composed of α chain p28 and β chain Epstain-Barr induce gene-3 (EBI3). The p28 subunit, or IL-30, has an important role as a part of IL-27, but it can be secreted as a separate monomer and has its own functions in the absence of EBI3. The discovery of IL-30 as individual cytokine is relatively new and thus its role in the modulation of the immune response is not fully understood.
Interleukin-26 (IL-26) is a protein that in humans is encoded by the IL26 gene.
Interleukin-22 (IL-22) is protein that in humans is encoded by the IL22 gene.
Interleukin 19 (IL-19) is an immunosuppressive protein that belongs to the IL-10 cytokine subfamily.
Signal transducer and activator of transcription 6 (STAT6) is a transcription factor that belongs to the Signal Transducer and Activator of Transcription (STAT) family of proteins. The proteins of STAT family transmit signals from a receptor complex to the nucleus and activate gene expression. Similarly as other STAT family proteins, STAT6 is also activated by growth factors and cytokines. STAT6 is mainly activated by cytokines interleukin-4 and interleukin-13.
T helper 17 cells (Th17) are a subset of pro-inflammatory T helper cells defined by their production of interleukin 17 (IL-17). They are related to T regulatory cells and the signals that cause Th17s to actually inhibit Treg differentiation. However, Th17s are developmentally distinct from Th1 and Th2 lineages. Th17 cells play an important role in maintaining mucosal barriers and contributing to pathogen clearance at mucosal surfaces; such protective and non-pathogenic Th17 cells have been termed as Treg17 cells.
T-box transcription factor TBX21, also called T-bet is a protein that in humans is encoded by the TBX21 gene. Though being for long thought of only as a master regulator of type 1 immune response, T-bet has recently been shown to be implicated in development of various immune cell subsets and maintenance of mucosal homeostasis.
Interleukin 35 (IL-35) is a recently discovered anti-inflammatory cytokine from the IL-12 family. Member of IL-12 family - IL-35 is produced by wide range of regulatory lymphocytes and plays a role in immune suppression. IL-35 can block the development of Th1 and Th17 cells by limiting early T cell proliferation.
The Interleukin-2 receptor alpha chain is a protein involved in the assembly of the high-affinity Interleukin-2 receptor, consisting of alpha (IL2RA), beta (IL2RB) and the common gamma chain (IL2RG). As the name indicates, this receptor interacts with Interleukin-2, a pleiotropic cytokine which plays an important role in immune homeostasis.
T helper 3 cells (Th3) are a subset of T lymphocytes with immunoregulary and immunosuppressive functions, that can be induced by administration of foreign oral antigen. Th3 cells act mainly through the secretion of anti-inflammatory cytokine transforming growth factor beta (TGF-β). Th3 have been described both in mice and human as CD4+FOXP3− regulatory T cells. Th3 cells were first described in research focusing on oral tolerance in the experimental autoimmune encephalitis (EAE) mouse model and later described as CD4+CD25−FOXP3−LAP+ cells, that can be induced in the gut by oral antigen through T cell receptor (TCR) signalling.
The Interleukin-1 family is a group of 11 cytokines that plays a central role in the regulation of immune and inflammatory responses to infections or sterile insults.
Type 1 regulatory cells or Tr1 (TR1) cells are a class of regulatory T cells participating in peripheral immunity as a subsets of CD4+ T cells. Tr1 cells regulate tolerance towards antigens of any origin. Tr1 cells are self or non-self antigen specific and their key role is to induce and maintain peripheral tolerance and suppress tissue inflammation in autoimmunity and graft vs. host disease.
Type 3 innate lymphoid cells (ILC3) are immune cells from the lymphoid lineage that are part of the innate immune system. These cells participate in innate mechanisms on mucous membranes, contributing to tissue homeostasis, host-commensal mutualism and pathogen clearance. They are part of a heterogeneous group of innate lymphoid cells, which is traditionally divided into three subsets based on their expression of master transcription factors as well as secreted effector cytokines - ILC1, ILC2 and ILC3.