R&D Systems Cytokines, Chemokines and Growth Factors

R&D Systems Cytokines, Chemokines and Growth Factors

Cytokine and Growth Factor Families


Cytokines are involved in most biological processes including embryonic development, disease pathogenesis, innate responses to infection, antigen-specific immunity, and cognitive changes. (1). One important hallmark of cytokines and growth factors is that they can play both beneficial and harmful roles, depending on context. For example, although IFNγ helps protect the body against intracellular microorganisms, it also plays a role in autoimmune diseases.

Early cytokine research began in the 1940s with studies of “soluble factors” that were produced by one cell and acted on by another cell (1). Fast forward to the 80s, and Natural TGF-beta was first purified and sold by R&D Systems in 1986 followed by the release of our first recombinant proteins in 1988. Today, we offer a complete range of proteins that undergo our rigorous quality testing to ensure both high activity and consistency. For more than 30 years, R&D Systems has been a trusted brand for cytokines and growth factors.

Read below for more information about the different categories of Cytokines, Chemokines, and Growth factors with links to their cell signaling pathways. You can also view cell signaling pathways categorized by research area.

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Interleukins are secreted cytokines that have complex immunomodulatory functions including cell proliferation, maturation, migration, adhesion, differentiation and activation (2). They are subdivided into several families based on sequence homology, evolutionary relationship, common receptor chain or major function. Known families include the IL1 family, the common ᵧ chain family, the IL-10 family, the IL-12 family, cytokines of Type 2 immune response, interleukins with chemokine activity, and other interleukins (3).

Interleukin Signaling Pathways

TGF-beta Superfamily – Activin, BMPs, GDFs, GDNF, TGF-beta

Members of this family are important to the development of multicellular organisms. Proteins in this family are involved in such cellular processes as embryonic stem cell self-renewal, gastrulation, differentiation, organ morphogenesis and adult tissue homeostasis (4). Furthermore, TGF-beta has both pro-tumor and anti-tumor roles. The TGF-beta superfamily signals via heteromeric complexes of type 1 and type 2 serine/threonine kinase receptors.

TGF-Beta Signaling Pathways


Chemotactic cytokines (Chemokines) play important roles in cell migration, immune system development and homeostasis. They are also involved in protective and destructive immune and inflammatory responses (5). Chemokines are organized into four sub-families—CC, CXC, CX3C and XC—which indicate the variation in the configuration of cysteines closest to the N terminus. Chemokines interact with glycosaminoglycans (GAGS), which is important for immobilization on cell surfaces and the extracellular matrix. Chemokines are active as monomers, homodimers and heterodimers. Other post-translational modifications that affect chemokines include citrullination, nitration/nitrosylation, and cleavage by a wide variety of enzymes.

Chemokine Signaling Pathways


As the name indicates, Fibroblast growth factors (FGFs) were originally identified in the context of promoting fibroblast proliferation. There are 22 FGF family members in humans, of which only 18 are ligands for FGF receptors (FGFRs) (6). FGFs initiate numerous signaling pathways including RAS/MAPK, PI3-Kinase/AKT and PLCγ. Many members of the FGF family have been connected to several therapeutic applications including ones for cardiovascular disease, cancer, hair growth, osteoarthritis, diabetes, and Parkinson’s disease among others. The function of several other FGFs remain unidentified.

FGF Signaling Pathways


Investigators first became aware of Epidermal growth factor (EGF) during seminal research of the newly discovered nerve growth factor (NGF). EGF was soon shown to be a ligand for the membrane-bound EGF receptor (EGFR), the first described receptor tyrosine kinase (7). EGF and other EGFR ligands (transforming growth factor alpha, amphiregulin, epigregulin betacellulin, heparain-binding EGF-like growth factor and epigen) all induce EGFR internalization and trafficking to early endosomes. EGFR is upregulated in a variety of cancers including non-small-cell cancer, metastatic colorectal cancer, glioblastoma, pancreatic cancer and breast cancer, among others.


Wnts are secreted hydrophobic proteins that mediate contact-dependent or short-distance cell-cell communication (8). Wnt-signaling pathways are divided into canonical, non-canonical and cell-polarity pathways. Using a wide variety of model systems, investigators have shown that Wnt signaling is important for many cellular processes including proliferation, cell-fate specification, differentiation and migration. It is important to note that although Wnts are commonly associated with development processes, the first mammalian Wnt gene (wnt) was identified as an oncogene. A role for Wnt signaling in cancer is bolstered by in silico data demonstrating frequent alterations (mutations, amplifications, deletions) of Wnt ligands and intracellular components in a variety of cancers (8).

Beta-Catenin-Dependent Wnt Signaling


Although Insulin-like Growth Factors (IGFs), have a structure similar to insulin, they tend to be more important for mediating long-term activities such as cell fate, while insulin is more important for metabolic activity (9). Unlike insulin, which is only secreted by pancreatic β cells, IGF is produced in a variety of tissues, and the specific cell type that secretes it has not been identified. IGF production increases with age into adulthood and declines after the age of 30.


Vascular endothelial growth factors (VEGFs) play important roles in blood vessel formation, maintenance and remodeling. The VEGF subtypes A-F are high-affinity ligands for the receptor tyrosine kinases VEGF receptor (VEGFRs) 1, 2, & 3. The VEGFs also bind to the co-receptors, neuropilin 1 & 2 (NRP1, NRP2) and heparan sulfate proteoglycans (HSPGs) (10). VEGF signaling is regulated by multiple variables including receptor expression, ligand affinity, co-receptor expression, non-VEGF binding-auxiliary proteins and tyrosine phosphatases (10).

VEGF-VEGFR2 Signaling Pathways


There are four known colony stimulating factors (CSFs) including granulocyte-macrophage-CSF (GM-CSF), macrophage colony formation CSF (M-CSF), granulocyte-CSF (G-CSF) and multi-CSF, also known as interleukin 3 (IL-3). CSFs are glycoproteins that have several functions including stimulating proliferation, suppressing apoptosis, maturation induction and differentiation commitment (11).


The angiopoietin (ANG)-tyrosine kinase with Ig and EGF homology domains (TIE) growth factor receptor pathway has emerged as a complementary target for vascular endothelial growth factor (VEGF) based anti-angiogenic cancer therapies (12). ANG1, ANG2, ANG3 (mouse), and ANG4 (human) are ligands of the TIE2 receptor. Although TIE 1 is currently considered an orphan receptor, it is activated via interaction with TIE 2. Increased ANG2 expression has been correlated with a variety of human cancers including, melanoma, renal cell carcinoma, glioblastoma, breast cancer and colorectal cancer (12). ANG2 has also been implicated in other ailments such as kidney disease, diabetes, liver cirrhosis asthma and heart disease. ANG1 expression has also been invoked in some of these ailments, alone and relative to ANG2 expression.


Platelet-derived growth factor (PDGF) has been shown to promote the proliferation, survival and migration of cells of mesenchymal origin (13). Various PDGF isoforms play a role in tumorigenesis and neurological diseases. As a therapeutic target, several approaches have been used to inhibit PDGF signaling.,These include using antibodies or aptamers to block ligand/receptor binding and PDGF receptor activation as well as using small molecules to block kinase signaling.

TNF Superfamily

Although Tumor Necrosis Factor (TNF) was initially described as a serum factor for inducing tumor necrosis, it is currently a therapeutic target in a variety of immune and inflammatory conditions (14). In addition to having pathogenic roles in inflammation, autoimmunity, tissue degeneration and tumorigenesis, TNF also has homeostatic functions such as regeneration, remyelination and remodeling.

TNF Superfamily Ligand Receptor Interactions


Members of the roof plate-specific spondin (R-Spondin) gene family were initially identified in fetal human brain and the roof plate of the mouse neural tube (15). R-spondin proteins are known to positively regulate canonical and non-canonical Wingless-related integration site (Wnt) signaling, which is important for organismal development, cellular behavior and cancer (16).


The term Interferon (IFN) was coined in 1957, to describe a “non-haemagglutinating macro molecular particle” that was shown to be responsible for viral interference (17). Currently, the 22 known IFNs are divided into 3 classes, I, II and III. In addition to antiviral effects shared by all IFN classes, class II, which consists of only IFNᵧ, is also a cancer therapeutic target (18).

Type I IFN Signaling Pathways

Type II IFN Signaling Pathways

Type III IFN Signaling Pathways


Brain-derived neurotrophic factor (BDNF) is a member of the well-studied neurotrophin family of ligands. Several isoforms exist, including pre-pro-BDNF, pro-BDNF and mature BDNF (m-BDNF) (19). The signal sequence of pre-pro-BDNF is cleaved in the golgi apparatus, producing pro-BDNF. Signaling responses to pro-BDNF have been correlated with neuronal fate, development and differentiation. Signaling responses downstream of m-BDNF have been associated with plasticity, neuronal growth and dendritic branching.


Stem Cell Factor (SCF) or c-kit ligand (KL) binds to the type III receptor tyrosine kinase c-kit or Kit to stimulate a number signaling pathways including MAPK and PI3K/AKT (20). SCF exists in both soluble and transmembrane forms, the regulation of which is determined at the mRNA and protein level. Overactivation of c-Kit has been associated with leukemia and the development of gastrointestinal stromal tumors (GISTs) which produce soluble SCF, (21).

Flt-3 Ligand

Fms-like target tyrosine kinase 3 ligand (or FL) is a hematopoietic cytokine that is often mutated or over-expressed in leukemia (22). It signals via its receptor Fms-like target tyrosine kinase 3 (Flt3), which is class 3 receptor tyrosine kinase receptor. Down stream signaling pathways include SHC, Grb2, Gab2, SHIP and the Ras/MAPK, PI3K and STAT pathways.


The glycoprotein, Leukemia Inducible Factor (LIF) was cloned in the late 1980s (23). It was shown that LIF induced macrophage differentiation in mouse M1 myeloid leukemia cells without stimulating progenitor cell proliferation. As such, there was great interest in LIF as a potential Leukemia therapeutic target. Unfortunately, subsequent studies have shown that although LIF held promise as a therapeutic promise, it is actually quite pleiotropic (24).

LIF Signaling Pathways

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