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Interleukin 1 alpha (IL-1α) is a member of the IL-1 family and a dual-function cytokine. Both the unprocessed precursor and a processed IL-1α protein signal through IL-1 receptor type 1 (IL-1R1). Various cells, including keratinocytes, thymic epithelium, hepatocytes, endothelial cells, fibroblasts, and the epithelial cells of mucous membranes, have high levels of intracellular IL-1α precursor. The precursor is also expressed on the surface of monocytes and B lymphocytes (Netea et al.). IL-1α recruits infiltrating cells to a site of injury during necrosis and plays an important role during processes of sterile inflammation (Cohen et al.; Rider et al.). During hypoxia, IL-1α contributes to angiogenesis (Carmi et al.). Studies in mice show that IL-1α is produced by microglia-like cells after ischemic brain injury, which contributes to the inflammation (Luheshi et al.).

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Fibroblast growth factor 21 (FGF-21) is a member of the FGF family. Using β-Klotho as a cofactor, FGF-21 signals through FGF receptor 1c and 4 to activate PI3K and MAPK pathways (Mattila and Härkönen; Kharitonenkov et al.). FGF-21 expression is regulated by tissue-specific peroxisome proliferator-activated receptors (PPARs). Upon PPAR-α stimulation FGF-21 is produced in the liver, and activation of PPAR-γ leads to FGF-21 production in adipose tissue. FGF-21 promotes insulin-independent glucose uptake and lipid accumulation in primary human adipocytes and in mouse 3T3-L1 cells. In pancreatic islets and INS-1 cells it inhibits glucose-mediated glucagon release and stimulates insulin production. FGF-21 does not induce proliferation in immortalized cell lines, unlike other FGFs (Kharitonenkov and Shanafelt). FGF-21 regulates thermogenesis in white and brown adipose tissue, and metabolic processes in cells of pancreatic origin (Kharitonenkov et al.).

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Fibroblast growth factor 6 (FGF-6) is a heparin-binding member of the FGF family, regulators of cell proliferation, differentiation, and function. FGF-6 binds and signals through the FGF receptors 1c, 2c, and 4 (Ornitz et al.). FGF-6 is a potent mitogen for fibroblasts, vascular endothelial cells, and prostate carcinoma cells (Asada et al.; Pizette et al.; Ropiquet et al.). FGF-6 is primarily expressed in epithelial and mesenchymal cell lineages. During development, FGF-6 is expressed in skeletal muscle, consistent with its role in muscle differentiation and regeneration (Floss et al.). FGF-6 has also been shown to promote chondrogenesis in embryonic somites in conjunction with transforming growth factor beta 2 (TGF-β2; Grass et al.).

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Macrophage inflammatory protein-1 alpha (MIP-1 alpha), also known as CCL3, is a member of the CC family of chemokines and is most closely related to CCL4 or MIP-1 beta. Mouse MIP-1 alpha signal through CCR1, CCR3, CCR5, and D6 receptors (Menten et al.). MIP-1 alpha exhibits a variety of proinflammatory activities in vitro, including leukocyte chemotaxis, cytokine production, and mast cell activation, and it inhibits the proliferation of hematopoietic stem cells in vitro and in vivo (Cook). MIP-1 alpha plays a critical role in macrophage recruitment into wounds and in tissue repair (DiPietro et al.). It has been demonstrated that blockade of the CCL3/MIP-1 alpha-CCR1 pathway blocks the recruitment of CCR1-expressing CD4+ T cells to the liver, showing a therapeutic potential for treating T cell-mediated liver diseases (Ajuebor et al.).

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Interleukin 2 (IL-2) is a monomeric cytokine that was originally identified as a T cell growth factor (Gaffen and Liu). It binds to heterotrimeric receptors consisting of CD25, CD122, and CD132. Upon binding, it activates JAK3-, STAT5-, and AKT-dependent signaling pathways, which results in cellular proliferation and survival (Ma et al.). The majority of IL-2 is secreted by activated CD4+ and CD8+ T cells, although B cells and dendritic cells were found to produce IL-2 in small amounts. IL-2 downregulates immune responses to prevent autoimmunity during thymic development, influences the development of CD4+CD25+ regulatory T cells, and affects development of follicular helper T cells. IL-2 also controls inflammation by inhibiting Th17 differentiation (Banchereau et al.). High IL-2 levels in serum are associated with progression of scleroderma, rheumatoid arthritis, and gastric and non-small cell lung cancer, though no known disease can be directly attributed to the lack or excess of IL-2 (Gaffen and Liu).

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Thrombopoietin (TPO) is a key regulator of megakaryocytopoiesis and thrombopoiesis in vitro and in vivo. TPO stimulates the proliferation and maturation of megakaryocytes and has an important role in regulating the level of circulating platelets in vivo (Bartley et al.; de Sauvage et al.; Foster et al.; Sohma et al.). TPO also promotes the survival, self-renewal, and expansion of hematopoietic stem cells and primitive multilineage progenitor cells. It is commonly used with other cytokines such as stem cell factor (SCF) and Flt3/Flk-2 ligand to promote expansion of primitive hematopoietic cells in culture (Hitchcock and Kaushansky). The TPO receptor, c-Mpl, is expressed at all stages of megakaryopoiesis, from hematopoietic stem and progenitor cells to mature platelets (Ng et al.).

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Thymus-expressed chemokine (TECK), or CCL25, is a member of the CC family of chemokines that regulates the movement of lymphocytes in the thymus and in the small intestine. TECK induces chemoattraction by binding the chemokine receptor CCR9, which is expressed on immature pre-T cells and thymocytes (Youn et al.; Uehara et al.). In the thymus, TECK is produced by stromal cells, whereas in the small intestine TECK is primarily produced by epithelial cells (Vicari et al.; Bowman et al.; Kunkel et al.). CCR9 is a G protein-coupled receptor and is expressed on most thymocytes, but not on natural killer cells, monocytes, eosinophils, basophils, and neutrophils (Wu et al). In Jurkat cells, binding of TECK to CCL9 has been shown to increase levels of intracellular calcium (Cheng-Rong et al). TECK/CCR9 signaling has also been linked to many cancers, as these molecules have been shown to mediate anti-apoptotic processes by activating the PI3K/AKT signaling pathway, weakening the effect of cytotoxic T cells by regulating STAT signaling. Additionally, TECK induces metastasis by increasing the expression of MMP2 and MMP9 (Tu et al.).

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Interleukin 6 (IL-6) is a pleiotropic growth factor with a wide range of biological activities in immune regulation, hematopoiesis, and oncogenesis. IL-6 is produced by a variety of cell types including T cells, B cells, monocytes and macrophages, fibroblasts, hepatocytes, vascular endothelial cells, and various tumor cell lines. On its own or in combination with other factors such as IL-2 and interferon-γ, IL-6 stimulates the proliferation of B cells, T cells, and hybridoma cells (Nordan et al.; Van Snick et al.; Gauldie et al.; Mihara et al.; Tanaka et al). In combination with cytokines such as IL-3, GM-CSF, and SCF, IL-6 has been shown to promote hematopoietic progenitor cell proliferation and differentiation in vitro. IL-6 signals through a cell surface type I cytokine receptor complex consisting of the ligand-binding IL-6α (CD126) and the signal-transducing gp130 subunits. The binding of IL-6 to its receptor system includes activation of the JAK/STAT signaling pathway (Mihara et al.; Peters et al; Tanaka et al.).

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Interleukin 1 alpha (IL-1α) is a member of the IL-1 family and a dual-function cytokine. Both the unprocessed precursor and a processed IL-1α protein signal through IL-1 receptor type 1 (IL-1R1). Various cells, including keratinocytes, thymic epithelium, hepatocytes, endothelial cells, fibroblasts, and the epithelial cells of mucous membranes have high levels of intracellular IL-1α precursor, which is also expressed on the surface of monocytes and B lymphocytes (Netea et al.). IL-1α recruits infiltrating cells to a site of injury during necrosis and plays an important role during processes of sterile inflammation (Rider et al.; Cohen et al.). During hypoxia, IL-1α contributes to angiogenesis (Carmi et al.). IL-1α is produced by microglia-like cells after ischemic brain injury, which contributes to the inflammation (Luheshi et al.).

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Mediate calcium phosphate clearance and prevent ectopic calcification with fetuin A, a plasma glycoprotein that forms soluble complexes with calcium and phosphate (Heiss et al.; Price and Lin). Belonging to the cystatin superfamily of cysteine protease inhibitors (Brown and Dziegielewska), fetuin A has also been shown to play a role in lipid transport, acting as a carrier (Kumbla et al.). In cell-based assays, it has been suggested that fetuin A protects against lethal systemic infection through the inhibition of high mobility group box 1 (HMGB1) protein accumulation and release (Li et al.). Fetuin A acts as a natural antagonist against specific TGF-β and BMP signaling proteins, blocking osteogenic differentiation of rat bone marrow cells (Demetriou et al.). This protein contains a His-residue tag at the carboxyl end of the polypeptide chain. For consistency and reproducibility across your applications, fetuin A from STEMCELL comes lyophilised with ≥94% purity, and endotoxin levels are verified to be ≤1.0 EU/μg protein.

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Neurotrophin-4 (NT-4) is a member of the nerve growth factor family which includes neurotrophin-3 (NT-3), brain-derived neurotrophic factor (BDNF), and nerve growth factor (NGF), all of which promote the differentiation, growth, and survival of peripheral and central nervous system neurons (Eide et al.). NT-4 binds and activates tropomyosin receptor kinase B (TrkB) at the cell surface; in doing so, it acts as a survival factor for certain populations of sensory neurons (Berkemeier et al.; Skaper). It has been shown that NT-4, together with BDNF, promotes neurite extension and maturation, as well as maintenance of differentiated cerebellar granule cells (Gao et al.).

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Leukemia inhibitory factor (LIF) is an interleukin 6 class cytokine that regulates a broad variety of developmental functions. After LIF binds to LIF receptor (LIFR), LIFR associates with gp130 and activates JAK/STAT and MAPK signaling (Auernhammer and Melmed; Suman et al.). LIFR activation of STAT3 is essential for maintaining the mouse embryonic stem cell phenotype (Niwa et al.). Produced by the endometrium, LIF plays an important autocrine and paracrine role in implantation by regulating proliferation, invasion, and differentiation of trophoblasts following blastocyst attachment (Auernhammer and Melmed; Suman et al.). Human LIF can be used for the maintenance of mouse embryonic stem cells, however mouse LIF cannot bind to the human receptor, thus rendering mouse LIF inactive (Dahéron et al.). LIF is produced by CD4+ and activated regulatory T cells, and promotes Foxp3 expression, while repressing Th17 lineage-specific genes (Metcalfe). LIF is also secreted by mesenchymal stromal cells, where it supports hematopoiesis and immune modulation (Nasef et al.).

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Monokine induced by interferon-gamma (MIG), or CXCL9, is a member of the CXC chemokine family. MIG is closely related to two other chemokines: CXCL10 and CXCL11, all of which signal through the CXCR3 receptor (Ding et al.). MIG is secreted by a variety of immune cells including T cells, NK cells, dendritic cells, macrophages, and eosinophils, as well as non-immune cells including hepatic stellate cells, preadipocytes, thyrocytes, endothelial cells, tumor cells, fibroblasts, and glial cells of the central nervous system. MIG has also been shown to act as a chemoattractant for activated T cells and for tumor-infiltrating leukocytes (TILs), but not for neutrophils or for monocytes. MIG has also been reported to be both a tumor suppressor and tumor promoter in various types of cancer.

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Heparin-binding epidermal growth factor (EGF)-like growth factor (HBEGF) is a member of the EGF family (Nishi and Klagsbrun). HBEGF promotes blastocyst adhesion to the uterine wall (Iwamoto and Mekada). It also plays a role in smooth muscle cell hyperplasia and brain injury (Nishi and Klagsburn). HBEGF produced by CD4+ T cells promotes wound healing by stimulating migration and proliferation of keratinocytes, fibroblasts, and smooth muscle cells (Blotnick et al.). It binds to EGFR, ErbB4, ErbB2, and ErbB3, activating the PI3K/AKT signaling cascade (Iwamoto and Mekada). HBEGF is produced in a variety of cells, where it contributes to physiological and pathological processes. HBEGF is overexpressed in ovarian, breast, gastric, colorectal, pancreatic, and endometrial cancers, which likely contributes to pathogenesis (Miyata et al.).

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SARS-CoV-2 Recombinant Spike Protein, aa319-541 is expressed in Pichia pastoris and is one of four structural proteins encoded by the SARS-CoV-2 genome. The Spike Protein plays a key role in attachment to host cells allowing invasion through clathrin-mediated endocytosis. The spike protein can be cleaved by host cell proteases after aa685 to yield the N-terminal S1 subunit, and C-terminal S2 region. The S1 subunit is responsible for interacting with the host cell receptor (angiotensin-converting enzyme II) through a receptor-binding domain that is highly conserved with SARS-CoV. The S1 subunit has two conformations: a ‘down’ conformation in which the receptor is inaccessible, and an ‘up’ conformation in which the receptor is accessible. These conformational changes are key for monoclonal antibody drugs and vaccine development. At the amino terminus of the polypeptide chain, SARS-CoV-2 Recombinant spike protein contains a polyhistidine tag and a SUMOstar site.

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Interleukin 12 (IL-12p70) is a heterodimeric cytokine composed of p35 and p40 subunits. IL-12 is produced by monocytes, macrophages, dendritic cells, neutrophils and B cells in response to bacterial products and cytokines such as IFN-γ. The IL-12 receptor is expressed on T, NK, and dendritic cells. Upon binding, IL-12 initiates signaling via the JAK/STAT signaling pathway and stimulates NK, B, and T cells to produce IFN-γ (Watford et al.). It also regulates cytokine synthesis, proliferation of T and NK cells, and stimulates differentiation of CD4+ and CD8+ T cells (Germann and Rüde). Mice that are deficient in IL-12 are susceptible to many intracellular pathogens and have impaired IFN-γ secretion, Th1 differentiation and NK cytolytic activity; however, Th2 development and IL-4 production are enhanced (Watford et al.).

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Human Interleukin 4 (IL-4) is important for immune responses to helminth infection as well as in allergic responses (Olpihant et al.). The IL-4 receptor consists of a heterodimer of IL-4Ra and common gamma chain. IL-4 receptor engagement leads to the activation of JAK1/3 and the recruitment of STAT6 and IRS1/2 (Nelms et al.). IL-4 drives immunoglobulin class switching in B cells (to IgE, IgG4), mast cell hyperplasia, mucus production, and the differentiation of naïve T cells into Th2 cells, which produce IL-4, IL-5, IL-10, and IL-13 (Bao et al.; Nelms et al.; Olpihant et al.). In addition to Th2 cells, IL-4 is produced by CD4+ NK T cells, γ/δ T cells, activated basophils, eosinophils, and mast cells. Human IL-4 does not cross-react with mouse cells (Park et al.).

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Fractalkine (CX3CL1) is a unique chemokine belonging to the CX3C family, and is characterized by a C-X3-C cysteine motif within the chemokine domain, near the amino terminus of the protein (Bazan et al.). The chemokine domain is connected to an extended mucin-like stalk, followed by a transmembrane region, and a C-terminal intracellular domain (Imai et al.; Jones et al.). The protein signals through interaction with a single receptor, CX3CR1, expressed on monocytes, natural killer cells, T cells, microglia, and smooth muscle cells. Fractalkine is upregulated in endothelial cells by inflammatory signals and is synthesized as a membrane-bound molecule that mediates cell migration and adhesion (White and Greaves). Cleavage at the base of the stalk by metalloproteinases generates a soluble chemokine, which functions as a potent chemoattractant of target cells (Garton et al.; Apostolakis and Spandidos). Fractalkine has been implicated in pathology of inflammatory diseases, such as atherosclerosis and other vascular diseases, and has anti-apoptotic functions (White and Greaves).

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Interleukin 6 receptor (IL-6R) alpha is a type I transmembrane glycoprotein that forms a complex with type I transmembrane signal transducer protein gp130 (CD130) and mediates the biological activities of IL-6. IL-6 binds to the membrane-bound non-signaling IL-6R alpha (mIL-6R), and the complex binds to two molecules of gp130 and leads to ‘classical’ IL-6-signal transduction, which includes activation of JAK/STAT, ERK, and PI3K signal transduction pathways (Scheller et al.). In contrast, a soluble form of IL-6R alpha (sIL-6R), which comprises the extracellular portion of the receptor, binds to the secreted IL-6 to form a complex that promotes bioavailability of IL-6. The complex of IL-6 and sIL-6R can bind to gp130 on cells that do not express the IL-6R and are unresponsive to IL-6. This process is known as trans-signaling (Hunter and Jones; Rose-John S). sIL-6R regulates both local and systemic IL-6-mediated events. Elevated levels of sIL-6R have been documented in several disease conditions such as rheumatoid arthritis, myeloma, and Crohn’s disease (Jones et al.; Mihara et al.).

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A type 1 membrane glycoprotein belonging to the immunoglobulin superfamily, cluster of differentiation 200 (CD200) binds the CD200 receptor (CD200R) that is expressed on the surface of myeloid cells and T cells (Wright et al.), and has been shown to inhibit myeloid cell activity and macrophage cytokine production (Jenmalm et al.). Homologues of CD200 have been identified in viruses and can interact with CD200R to reduce macrophage pro-inflammatory cytokine production (Foster-Cuevas et al.). Studies have shown that the immunosuppressive effects of CD200 can promote acceptance of allogeneic tissue grafts in hosts (Gorczynski et al.), whereas dysregulation of CD200/CD200R can contribute to the development of autoimmune conditions, such as rheumatoid arthritis (Ren et al.). CD200 contains two immunoglobulin-like domains, a V-type domain and a smaller C2-type domain (Hatherley et al.). This protein contains a His-residue tag at the carboxyl end of the polypeptide chain. For consistency and reproducibility across your applications, cluster of differentiation 200 from STEMCELL comes lyophilised with ≥95% purity, and is verified by LAL analysis to ensure endotoxin levels are ≤1,0 EU/μg protein. Human recombinant CD200 at 2 μg/ml can bind human CD200R (His and hFc tag) with a linear range of 5 to 28 ng/ml, as determined by functional ELISA.

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Vascular endothelial growth factor (VEGF-165) is a heparin-binding homodimeric glycoprotein involved in embryonic vasculogenesis and angiogenesis. VEGF binds to VEGFR-1 (R1) and VEGFR-2 (R2), and activates Raf/MEK/ERK and PI3K/AKT pathways (Ferrara et al.). It plays an important role in neurogenesis both in vitro and in vivo (Storkebaum et al.). It has neurotrophic effects on neurons of the central nervous system and promotes growth and survival of dopaminergic neurons and astrocytes. VEGF also promotes growth and survival of vascular endothelial cells, monocyte chemotaxis, and colony formation by granulocyte-macrophage progenitor cells (Ferrara et al.). VEGF-165 contains two polypeptide chains of 165 amino acids each. This product is animal component-free.

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Platelet-derived growth factor (PDGF) is a dimeric glycoprotein consisting of two disulfide bridge-stabilized polypeptide chains, A and B, which are assembled as heterodimers (PDGF-AB) or homodimers (PDGF-AA and PDGF-BB) (Fretto et al.; Westermark and Heldin). PDGF signals through the receptor tyrosine kinases PDGFRalpha and PDGFRbeta. It has been shown that PDGF-induced migration involves signaling pathways involving MEK/ERK, EGFR, Src, and PI3K/AKT (Kim et al.). PDGF is a potent mitogen for cells of mesenchymal origin- like fibroblasts, glial cells, and vascular smooth muscle cells. PDGF has been implicated in pathogenesis of atherosclerosis, glomerulonephritis, cancer, and in the contraction of vascular smooth muscle cells of rat aortic tissues (Fretto et al.; Sachinidis et al.). It has been shown that PDGF-AB together with 5-Azacytidine (Catalog #72012), induces the conversion of mature bone and fat cells into tissue-regenerative multipotent stem cells (Chandrakanthan et al.).

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Heparin-binding epidermal growth factor (EGF)-like growth factor (HBEGF) is a member of the EGF family (Nishi and Klagsbrun). HBEGF promotes blastocyst adhesion to the uterine wall (Iwamoto and Mekada). It also plays a role in smooth muscle cell hyperplasia and brain injury (Nishi and Klagsburn). HBEGF produced by CD4+ T cells promotes wound healing by stimulating migration and proliferation of keratinocytes, fibroblasts, and smooth muscle cells (Blotnick et al.). It binds to EGFR, ErbB4, ErbB2, and ErbB3, activating the PI3K/AKT signaling cascade (Iwamoto and Mekada). HBEGF is produced in a variety of cells, where it contributes to physiological and pathological processes. HBEGF is overexpressed in ovarian, breast, gastric, colorectal, pancreatic, and endometrial cancers, which likely contributes to pathogenesis (Miyata et al.). This product is animal component-free.

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Human Interleukin 4 (IL-4) is important for immune responses to helminth infection as well as in allergic responses (Olpihant et al.). The IL-4 receptor consists of a heterodimer of IL-4Ra and common gamma chain. IL-4 receptor engagement leads to the activation of JAK1/3 and the recruitment of STAT6 and IRS1/2 (Nelms et al.). IL-4 drives immunoglobulin class switching in B cells (to IgE, IgG4), mast cell hyperplasia, mucus production, and the differentiation of naïve T cells into T helper type 2 (Th2) cells, which produce IL-4, IL-5, IL-10, and IL-13 (Bao et al.; Olpihant et al.; Nelms et al.). In addition to Th2 T cells, IL-4 is produced by CD4+ NK T cells, γ/δ T cells, activated basophils, eosinophils, and mast cells. IL-4 consists of 130 amino acids with a predicted molecular weight of 15.1 kDa. Human IL-4 does not cross-react with mouse cells (Park et al.). This product is animal component-free.

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Lipocalin-2 (LCN2) is a member of the lipocalin superfamily, which share a highly conserved fold containing an eight-stranded antiparallel beta barrel (Flower), and transport small hydrophobic molecules. Playing a role in innate immunity, Lipocalin-2 acts as a potent bacteriostatic reagent by sequestering iron-containing siderophores (Flo et al.). It is mainly expressed in activated neutrophils, but is also secreted by other immune cells in response to infection. Lipocalin-2 has been implicated in multiple cellular processes, such as differentiation (Yang et al.), migration (Du et al.), and apoptosis (Devireddy et al.). In vitro studies suggest that lipocalin-2 is a potential therapeutic target for certain cancers, including colorectal cancer (CRC; Zhang et al.) and chronic lymphocytic leukemia (Bauvois et al.). This protein product contains a His-residue tag at the carboxyl end of the polypeptide chain. For consistency and reproducibility across your applications, lipocalin-2 from STEMCELL comes lyophilised with ≥94% purity, and endotoxin levels are verified to be ≤1.0 EU/μg protein.

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Interleukin 10 (IL-10) is the founding member of the IL-10 family of class II cytokines. All of the IL-10 cytokine family members have a four-helix bundle consisting of α-helical folds. Upon binding to its receptor, IL-10 activates signaling through JAK1 and STAT3. It is produced by dendritic cells, macrophages, and CD4+ T regulatory cells, as well as mast cells, NK cells, neutrophils, and regulatory B cells, under specific stimulating conditions (Saraiva and O'Garra). IL-10 can inhibit the activation of certain immune cells while it promotes the function of B cells, and facilitate healing process. Specifically, this cytokine is important for the function of T regulatory cells as it is a potent suppressor of effector T cell proliferation and cytokine production. Also, IL-10 produced by a subset of macrophages inhibits activation and production of pro-inflammatory cytokines by neighboring macrophages, thus allowing a level of self-regulation. IL-10 enhances B cell proliferation, immunoglobulin secretion, and class II MHC expression (Ouyang et al.).

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Tumor necrosis factor-alpha (TNF-α) is a pro-inflammatory cytokine that activates NF-κB, MAPK, and PI3K/AKT pathways. Activated T cells and macrophages are the primary producers of TNF-α in response to inflammation and infectious conditions. Many other cell types have been shown to produce TNF-α, among them B cells, NK cells, mast cells, neutrophils, dendritic cells, microglia, endothelial cells, smooth muscle cells, cardiomyocytes, and fibroblasts. TNF-α has cytotoxic effects on cancerous cells by stimulating anti-tumor immunosuppressive responses. TNF-α stimulates expression of E- and P-selectins, thus facilitating adhesion of neutrophils, monocytes, and memory T cells to activated platelets and endothelial cells (Zelová and Hošek). Other effects of TNF-α include vasodilatation and edema formation. In vitro studies of adult rat neural progenitor cells (NPCs) demonstrate that TNF-α reduces neurogenesis in dentate gyrus-derived NPCs, and promotes astrogliogenesis in subventricular zone-derived NPCs (Borsini et al.).

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Midkine is a member of a unique family of heparin-binding growth factors that are structurally different from other fibroblast growth factors (Muramatsu; Takada et al.). Midkine is a proinflammatory cytokine, promoting the migration of leukocytes, fibrinolysis, and acting as a chemotactic agent towards neutrophils (Muramatsu; Said et al.; Takada et al.). It also regulates growth, differentiation, and development during the midgestion stage of embryogenesis, and promotes angiogenesis (Muramatsu; Said et al.; Takada et al.). The protein structure consists of three antiparallel β-sheets and is highly conserved between species (Muramatsu; Takada et al.). While the exact signal pathway is not known, proposed pathways include promoting LRP, inhibiting Src kinase, activating paxillin and STAT1α, activating PI2 and MAP kinases, suppressing caspases, binding to α6β1-integrin and tetraspanin, activating FAK, phosphorylating STAT3, suppressing STAT5 phosphorylation, activating ALK, activating PI3 kinase and transcription of NFkB, binding to neuroglycan C or nucleolin, and binding to eIF3 (Muramatsu). In cultured cells, midkine influences growth and survival of neural precursor cells, synthesis of cytokines from endothelial and renal epithelial cells, and promotes synthesis of extracellular matrices from fibroblasts (Muramatsu; Takada et al.).

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R-Spondin-1 (RSPO1) is the prototype member of the R-Spondin (RSPO) protein subfamily of a superfamily of thrombospondin type 1 repeat (TSR-1)-containing proteins (Chen et al.; Kamata et al.; Kazanskaya et al.; Kim et al.). Although unable to initialize signaling, RSPO family members are potent enhancers of WNT signaling (Cruciat and Niehrs; de Lau et al.; Kamata et al.; Kazanskaya et al.). They are characterized by a TSR-1 domain, a carboxy-terminal region with positively charged amino acids, and two N-terminal furin-like cysteine-rich repeats (Glinka et al.; Kazanskaya et al.). R­-Spondin-1 activates β­-catenin signaling via the WNT signaling cascade and by indirectly increasing low-density lipoprotein receptor-related protein 6 (LRP6) on the cell surface. It does this by binding leucine-rich repeat-containing G-protein-coupled receptor 5 (LGR5), and competing with WNT antagonist DKK­1 for binding to the WNT co­receptors, Kremen and LRP­6, which reduces DKK­1-­mediated internalization of LRP6 (Binnerts et al.). RSPO1 is involved in a wide range of pleiotropic roles during embryogenesis, it is required for the specification of hematopoietic stem cells, and it has been shown to be important in the growth, survival, and migration of ovarian cancer cells (Cruciat and Niehrs; de Lau et al.; Genthe and Clements; Liu et al.).

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Vascular endothelial growth factor D (VEGF-D) is a member of the VEGF/platelet-derived growth factor (PDGF) family of proteins. VEGF-D is a potent angiogenic factor and promotes lymphangiogenesis, endothelial cell growth and survival, and can affect blood vessel permeability. VEGF-D is expressed in the lung, heart, small intestine, fetal lung, and at lower levels in the pancreas, colon, and skeletal muscle (Otrock et al.; Roy et al.; Stacker et al.; Yamada et al.). VEGF-D is a ligand for VEGF receptors 2 (Flk1) and 3 (Flt4) (Baldwin et al.). VEFGR-3 is highly expressed in lymphatic endothelial cells and is essential for their growth and differentiation (Otrock et al.; Roy et al.). Binding of VEGF-D to neuropilins contributes to VEGFR-3 signaling during lymphangiogenesis, whereas binding to integrin α9β1 promotes endothelial cell adhesion and migration (Roy et al.; Otrock et al.). During embryogenesis, VEGF-D also plays a role in the formation of the venous and lymphatic systems.