Thymic stromal lymphopoietin (TSLP) is a protein belonging to the cytokine family. It is known to play an important role in the maturation of T cell populations through activation of antigen presenting cells.
TSLP is produced mainly by non-hematopoietic cells such as fibroblasts, epithelial cells and different types of stromal or stromal-like cells.[ citation needed ] These cells are located in regions where TSLP activity is required.
TSLP production has been observed in various species, including humans and mice. In humans TSLP is encoded by the TSLP gene. [5] [6] Alternative splicing of this gene results in two transcript variants. [6]
It mainly impacts myeloid cells and induces the release of T cell-attracting chemokines from monocytes [ citation needed ] and enhances the maturation of myeloid (CD11c+) dendritic cells. [7] TSLP has also been shown to activate the maturation of a specific subset of dendritic cells located within the epidermis, called Langerhans cells. [8] Within the thymus TSLP activation of both myeloid and plasmacytoid (CD123+) dendritic cells results in the production of regulatory T cells. [9] [10]
TSLP signals through a heterodimeric receptor complex composed of the thymic stromal lymphopoietin receptor CRLF2 and the IL-7R alpha chain. After binding STAT5 phosphorylation is induced, resulting in the expression of upstream transcription factors. [11]
TSLP expression is linked to many disease states including asthma, [12] inflammatory arthritis, [13] atopic dermatitis, [8] eczema, eosinophilic esophagitis and other allergic states. [14] [15] The factors inducing the activation of TSLP release are not clearly defined.
Expression of TSLP is enhanced under asthma-like conditions (aka Airway HyperResponsiveness or AHR model in the mouse), conditioning APCs in order to orient the differentiation of T cells coming into the lungs towards a TH2 profile (T helper 2 pathway).[ citation needed ] The TH2 cells then release factors promoting an inflammatory reaction following the repeated contact with a specific antigen in the airways [ citation needed ].
TSLP-activated Langerhans cells of the epidermis induce the production of pro-inflammatory cytokines like TNF-alpha by T cells potentially causing atopic dermatitis. [8] It is thought that understanding the mechanism of TSLP production and those potential substances that block the production, one may be able to prevent or treat conditions of asthma and/or eczema. [16]
The TSLP signaling axis is an attractive therapeutic target. Amgen's Tezepelumab, a monoclonal antibody which blocks TSLP, is currently in phase III clinical trials for the treatment of asthma. [17] Fusion proteins consisting of TSLPR and IL-7Rα which can trap TSLP with excellent affinity have also been designed. [18] Additional approaches towards TSLP/TSLPR inhibition include peptides derived from the TSLP:TSLPR interface, [19] natural products [20] and computational fragment-based screening. [21]
Dendritic cells (DCs) are antigen-presenting cells of the mammalian immune system. Their main function is to process antigen material and present it on the cell surface to the T cells of the immune system. They act as messengers between the innate and the adaptive immune systems.
Plasmacytoid dendritic cells (pDCs) are a rare type of immune cell that are known to secrete large quantities of type 1 interferon (IFNs) in response to a viral infection. They circulate in the blood and are found in peripheral lymphoid organs. They develop from bone marrow hematopoietic stem cells and constitute < 0.4% of peripheral blood mononuclear cells (PBMC). Other than conducting antiviral mechanisms, pDCs are considered to be key in linking the innate and adaptive immune systems. However, pDCs are also responsible for participating in and exacerbating certain autoimmune diseases like lupus. pDCs that undergo malignant transformation cause a rare hematologic disorder, blastic plasmacytoid dendritic cell neoplasm.
Interleukin 21 (IL-21) is a protein that in humans is encoded by the IL21 gene.
Interleukin 33 (IL-33) is a protein that in humans is encoded by the IL33 gene.
Interleukin-25 (IL-25) – also known as interleukin-17E (IL-17E) – is a protein that in humans is encoded by the IL25 gene on chromosome 14. IL-25 was discovered in 2001 and is made up of 177 amino acids.
Cluster of differentiation 80 is a B7, type I membrane protein that is in the immunoglobulin superfamily, with an extracellular immunoglobulin constant-like domain and a variable-like domain required for receptor binding. It is closely related to CD86, another B7 protein (B7-2), and often works in tandem, binding to the same receptors to prime T cells.
Cluster of Differentiation 86 is a protein expressed on dendritic cells, macrophages, B-cells, and other antigen-presenting cells. Along with CD80, CD86 provides costimulatory signals necessary for T-cell activation and survival. Depending on the ligand bound, CD86 can be used to signal for self-regulation and cell-cell association, or for attenuation of regulation and cell-cell disassociation.
Chemokine ligand 18 (CCL18) is a small cytokine belonging to the CC chemokine family. The functions of CCL18 have been well studied in laboratory settings, however the physiological effects of the molecule in living organisms have been difficult to characterize because there is no similar protein in rodents that can be studied. The receptor for CCL18 has been identified in humans only recently, which will help scientists understand the molecule's role in the body.
OX40L is the ligand for OX40 and is stably expressed on many antigen-presenting cells such as DC2s, macrophages, and activated B lymphocytes.
Toll-like receptor 6 is a protein that in humans is encoded by the TLR6 gene. TLR6 is a transmembrane protein, member of toll-like receptor family, which belongs to the pattern recognition receptor (PRR) family. TLR6 acts in a heterodimer form with toll-like receptor 2 (TLR2). Its ligands include multiple diacyl lipopeptides derived from gram-positive bacteria and mycoplasma and several fungal cell wall saccharides. After dimerizing with TLR2, the NF-κB intracellular signalling pathway is activated, leading to an pro-inflammatory cytokine production and activation of innate immune response. TLR6 has also been designated as CD286.
C-C chemokine receptor type 7 is a protein that in humans is encoded by the CCR7 gene. Two ligands have been identified for this receptor: the chemokines ligand 19 (CCL19/ELC) and ligand 21 (CCL21).
Programmed death-ligand 1 (PD-L1) also known as cluster of differentiation 274 (CD274) or B7 homolog 1 (B7-H1) is a protein that in humans is encoded by the CD274 gene.
LIGHT, also known as tumor necrosis factor superfamily member 14 (TNFSF14), is a secreted protein of the TNF superfamily. It is recognized by herpesvirus entry mediator (HVEM), as well as decoy receptor 3.
Triggering receptor expressed on myeloid cells 1 is a protein that in humans is encoded by the TREM1 gene.
Killer cell lectin-like receptor subfamily B, member 1, also known as NK1.1, KLRB1, NKR-P1A or CD161, is a human gene.
Cytokine receptor-like factor 2 is a protein that in humans is encoded by the CRLF2 gene. It forms a ternary signaling complex with TSLP and interleukin-7 receptor-α, capable of stimulating cell proliferation through activation of STAT3, STAT5 and JAK2 pathways and is implicated in the development of the hematopoietic system. Rearrangement of this gene with immunoglobulin heavy chain gene (IGH), or with P2Y purinoceptor 8 gene (P2RY8) is associated with B-progenitor- and Down syndrome- acute lymphoblastic leukemia (ALL).
Interleukin-7 receptor subunit alpha (IL7R-α) also known as CD127 is a protein that in humans is encoded by the IL7R gene.
Chemorepulsion is the directional movement of a cell away from a substance. Of the two directional varieties of chemotaxis, chemoattraction has been studied to a much greater extent. Only recently have the key components of the chemorepulsive pathway been elucidated. The exact mechanism is still being investigated, and its constituents are currently being explored as likely candidates for immunotherapies.
Interleukin-23 (IL-23) is a heterodimeric cytokine composed of an IL12B (IL-12p40) subunit and the IL23A (IL-23p19) subunit. IL-23 is part of IL-12 family of cytokines. A functional receptor for IL-23 has been identified and is composed of IL-12R β1 and IL-23R. Adnectin-2 is binding to IL-23 and compete with IL-23/IL-23R. mRNA of IL-23R is 2,8 kB in length and includes 12 exons. The translated protein contains 629 amino acids, which is a type I penetrating protein includes signal peptide, an N-terminal fibronectin III-like domain and an intracellular part contains 3 potential tyrosine phosphorylation domains. There are 24 variants of splicing of IL-23R in mitogen-activated lymphocytes. IL-23R has some single nucleotide polymorphisms in the domain of binding IL-23 so there can be differences in activation of Th17. There is also variant of IL-23R which has just extracellular part and it´s known as soluble IL-23R. This form can compete with membrane form to bind IL-23 and there can be difference in activation of Th17 immune response and regulation of inflammation and immune function.
In cell biology, TH9 cells are a sub-population of CD4+T cells that produce interleukin-9 (IL-9). They play a role in defense against helminth infections, in allergic responses, in autoimmunity, and tumor suppression.