Signal Regulatory Protein α (SIRPα) is a monomeric approximately 90 kD type I transmembrane glycoprotein. The 504 amino acid human SIRPα contains two Ig-like C1-type domains and one Ig-like V-type domain. SIRPα can express in various tissues, mainly on brain and myeloid cells, including macrophages, neutrophils, dendritic and Langerhans cells. It also can detect in neurons, smooth muscle and endothelial cells. SIRPA is an immunoglobulin-like cell surface receptor for CD47. SIRPα acts as docking protein and induces translocation of PTPN6, PTPN11 and other binding partners from the cytosol to the plasma membrane. SIRPα shows adhesion of cerebellar neurons, neurite outgrowth and glial cell attachment. SIRPα engagement generally produces a negative regulatory signal; it may mediate negative regulation of phagocytosis, mast cell activation and dendritic cell activation
Thymic stromal lymphopoietin (TSLP) is a protein belonging to the cytokine family, contains 140 amino acids. It is known to play an important role in the maturation of T cell populations through activation of antigen presenting cells. TSLP induces the release of T-cell-attracting chemokines from monocytes and, in particular, enhances the maturation of CD11c+ dendritic cells. It can induce allergic inflammation by directly activating mast cells. TSLP is produced mainly by non-hematopoietic cells such as fibroblasts, epithelial cells and different types of stromal or stromal-like cells. These cells are located in regions where TSLP activity is required.
T cell immunoreceptor with Ig and ITIM domains (TIGIT), also called VSIG9 and Vstm3, is a member of the CD28 family within the Ig superfamily of proteins. TIGIT contains an immunoglobulin variable domain, a transmembrane domain and an immunoreceptor tyrosine-based inhibitory motif (ITIM), and is expressed on regulatory, memory, activated T cells and NK cells. TIGIT binds to CD155(PVR) that appear on dendritic cells (DC), macrophages and endothelium with high affinity, and CD112(PVRL2) with lower affinity, but not CD113 (PVRL3). TIGIT-Fc fusion protein could interact with PVR on DC and enhance the secretion of IL-10, but inhibit the macrophage activation. Mice lacking TIGIT show increased T cell responses and susceptibility to autoimmune challenges, while knockdown of TIGIT with siRNA in human memory T cells did not affect T cell responses.
T cell immunoglobulin and mucin domain 3 is a member of the TIM family of immune regulating molecules. Mature cynomolgus TIM3 consists of a 182 amino acid (aa)extracellular domain (ECD), a 21 aa transmembrane segment, and a 78 aa cytoplasmic tail. TIM3 is up-regulated on several populations of activated myeloid cells (macrophage, monocyte, dendritic cell, microglia, mast cell) and T cells (Th1, CD8+, NK, Treg). Its binding to Galectin9 induces a range of immunosuppressive functions which enhance immune tolerance and inhibit anti-tumor immunity. TIM3 ligation attenuates CD8+ and Th1 cell responses and promotes the activity of Treg and myeloid derived suppressor cells. TIM3 interactions with Galectin-9 can trigger immune stimulatory effects, such as the coactivation of NK cell cytotoxicity.
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