GM-CSF, IL-3, and IL-5 integrate hematopoietic and immune signals through the shared βc chain, respectively regulating myeloid cells, basophils, and eosinophils, and participating in hematologic malignancies, allergy, and autoimmune inflammation.

Keywords: βc family; common β chain; CD131; CSF2RB; GM-CSF; IL-3; IL-5; hematopoietic regulation; JAK2; STAT5; myeloid cells; eosinophils

1 Composition and Biological Positioning of βc Family Cytokines

1.1 Composition of βc Family Cytokines

The βc family consists of granulocyte-macrophage colony-stimulating factor (GM-CSF), interleukin-3 (IL-3), and interleukin-5 (IL-5). These three cytokines bind their respective specific receptor α chains and jointly recruit the βc chain CD131 to form signaling complexes. The α chain is responsible for ligand recognition and target cell selection, whereas the βc chain is responsible for high-affinity receptor assembly and intracellular signal transduction.

1.2 Functional Division Among GM-CSF, IL-3, and IL-5

(1) GM-CSF

GM-CSF mainly acts on myeloid progenitors, monocytes, macrophages, dendritic cells, neutrophils, and eosinophils. It promotes myeloid cell survival, maturation, and functional activation, and participates in alveolar macrophage differentiation and clearance of pulmonary surfactant.

(2) IL-3

IL-3 has a broader range of action and can support the survival and expansion of early hematopoietic progenitors, myeloid precursors, basophils, and mast cells. It also participates in emergency hematopoiesis, allergic responses, and survival of some myeloid tumor cells.

(3) IL-5

IL-5 mainly regulates the eosinophil lineage. It promotes differentiation of eosinophil precursors, prolongs the survival of mature eosinophils, and enhances their migration, degranulation, and tissue infiltration.

1.3 Shared βc Chain and Ligand Specificity

Although GM-CSF, IL-3, and IL-5 share CD131, they do not produce completely identical biological effects.

(1) The three cytokines use GM-CSFRα, IL-3Rα, and IL-5Rα respectively, and the expression range of the specific α chain determines the ability of cells to respond to different ligands.

(2) The tissue source, release timing, and local concentration of cytokines differ, allowing them to participate in steady-state hematopoiesis, infection responses, allergic reactions, or chronic inflammation.

(3) Differences in transcription factors, metabolic state, and cooperating receptors within target cells allow similar downstream signals to generate different differentiation and effector outcomes.

2 Structural Features of GM-CSF, IL-3, and IL-5 Receptor Complexes

2.1 Ligand-Specific Receptor α Chains

(1) GM-CSFRα/CD116

GM-CSFRα is encoded by the CSF2RA gene and is responsible for recognizing GM-CSF. After GM-CSFRα recruits the βc chain, a complete signaling receptor is formed, promoting myeloid cell survival, differentiation, and activation.

(2) IL-3Rα/CD123

IL-3Rα is encoded by the IL3RA gene and is responsible for IL-3 recognition. It is mainly expressed on some hematopoietic progenitors, basophils, plasmacytoid dendritic cells, and some myeloid tumor cells.

(3) IL-5Rα/CD125

IL-5Rα is encoded by the IL5RA gene and is mainly expressed on eosinophils and their precursor cells. Its relatively restricted expression is an important basis for the eosinophil selectivity of IL-5.

2.2 Shared βc Chain CD131

The βc chain is encoded by the CSF2RB gene and belongs to the type I cytokine receptor family. It is composed of an extracellular region, a single transmembrane region, and a cytoplasmic region. The βc chain itself does not possess protein kinase activity. Its cytoplasmic region can bind JAK2 and, after receptor assembly, provides recruitment sites for signaling molecules such as STAT5, Shc, and PI3K. In the absence of the βc chain, specific α chains may still bind ligands, but it is difficult to effectively initiate complete proliferation, survival, and differentiation signals.

2.3 Assembly Process of Receptor Complexes

Cytokines first bind their corresponding specific α chains and then recruit the βc chain to form signaling-competent receptor complexes. After receptor chains rearrange and cluster, JAK2 bound to the βc cytoplasmic region comes into proximity and becomes activated. Complexes formed by different ligands differ in stability and higher-order assembly, which can further affect signal intensity, duration, and downstream pathway bias.

Figure 1. Schematic of βc Chain Sharing and Downstream Signaling by the GM-CSF, IL-3, and IL-5 Receptors

2.4 Differences Between Human and Mouse IL-3 Receptor Systems

The human IL-3 receptor is mainly composed of CD123 and the βc chain. In mice, in addition to the shared βc chain, there is also an IL-3-specific β chain, βIL-3, which can transmit IL-3 signals together with mouse IL-3Rα. Therefore, when using mouse cells or animal models to study IL-3, the roles of the shared βc chain and the mouse-specific βIL-3 chain should be distinguished. The mouse IL-3 receptor system should not be fully equated with the human CD123/βc system.

3 Shared Signal Transduction Mechanisms Mediated by CD131/βc

3.1 JAK2-STAT5 Signaling

After receptor complex formation, JAK2 bound to the βc chain is activated and phosphorylates tyrosine residues in the βc cytoplasmic region. STAT5 is recruited to the receptor complex, undergoes phosphorylation and dimerization, and then enters the nucleus to regulate gene expression.

(1) Regulates cell survival-related genes such as BCL-2 and BCL-XL.

(2) Regulates cell proliferation-related genes such as MYC and Cyclin D.

(3) Maintains differentiation and effector functions of myeloid cells, basophils, and eosinophils.

3.2 RAS-RAF-MEK-ERK Signaling

After βc chain phosphorylation, adaptor proteins such as Shc, Grb2, and SOS can be recruited to activate the RAS-RAF-MEK-ERK pathway. ERK can promote hematopoietic progenitor expansion and cell cycle entry, and in mature myeloid cells it regulates adhesion, migration, degranulation, and inflammatory mediator expression.

3.3 PI3K-AKT-mTOR Signaling

After PI3K connects with the receptor signaling complex, AKT and mTOR-related signaling can be activated to maintain cellular metabolism, protein synthesis, and anti-apoptotic capacity. This supports survival of mature eosinophils, basophils, and some myeloid tumor cells. When continuously activated, this pathway may also reduce cellular sensitivity to growth factor withdrawal and drug-induced apoptosis.

3.4 Signal Negative Feedback and Receptor Internalization

(1) SOCS proteins

SOCS family proteins can bind JAK2 or receptor phosphorylation sites and inhibit sustained STAT5 activation.

(2) Protein tyrosine phosphatases

Phosphatases such as SHP can remove phosphate groups from JAK2, the βc chain, and downstream signaling proteins.

(3) Receptor internalization and degradation

After ligand stimulation, receptor complexes can undergo endocytosis and be cleared through lysosomal or other protein degradation pathways, reducing sustained signal input on the cell surface.

4 Regulation of Hematopoietic Cell Growth, Differentiation, and Activation by βc Family Cytokines

4.1 Survival and Lineage Differentiation of Hematopoietic Progenitors

IL-3 can support the survival of relatively early hematopoietic progenitors and multiple types of myeloid precursor cells, enhancing cell proliferation and colony formation. GM-CSF is more biased toward expansion and maturation of the granulocyte-monocyte lineage, whereas IL-5 mainly promotes eosinophil lineage differentiation. The effects of these three cytokines are also influenced by stem cell factor, FLT3 ligand, G-CSF, and other hematopoietic factors.

4.2 Monocytes and Macrophages

GM-CSF can promote monocyte and macrophage survival and enhance phagocytosis, antigen presentation, inflammatory cytokine production, and tissue migration. The macrophage state induced by GM-CSF is influenced by tissue origin, stimulation intensity, and local cytokine environment, and cannot be summarized simply as a single inflammatory or repair phenotype.

4.3 Dendritic Cells

GM-CSF is commonly used for in vitro induction of monocyte-derived dendritic cells and can support cell survival, differentiation, and antigen presentation function. These in vitro-induced cells are not fully equivalent to all dendritic cell subsets in vivo and usually need to be evaluated using phenotypes such as CD11c, HLA-DR, CD80, and CD86, as well as T cell-stimulatory capacity.

4.4 Basophils and Mast Cells

IL-3 can prolong basophil survival, increase their sensitivity to allergen and IgE receptor crosslinking signals, and enhance the release of histamine, lipid mediators, and cytokines. Mast cell dependence on IL-3 varies by species and tissue. Mouse bone marrow-derived mast cells usually respond strongly to IL-3, whereas mature human mast cells are more commonly co-regulated by factors such as SCF.

4.5 Eosinophils

IL-5 promotes maturation of eosinophil precursors and enhances survival, migration, and degranulation of mature cells. After eosinophils enter inflammatory tissues, GM-CSF and IL-3 can also prolong their lifespan, allowing local inflammation to persist.

Table 1. Receptor Composition and Main Functions of βc Family Cytokines

5 βc Signaling Abnormalities in Tumors, Allergy, and Autoimmune Diseases

5.1 IL-3/CD123 Signaling in Myeloid Tumors

CD123 can be highly expressed in blastic plasmacytoid dendritic cell neoplasm and some acute myeloid leukemia cells. After IL-3 binds CD123 and recruits the βc chain, JAK2-STAT5 and PI3K-AKT signaling can be enhanced to support tumor cell survival. Some myeloid tumors may also sustain βc-related pathway activation through receptor overexpression, kinase abnormalities, or signaling cross-talk. High CD123 expression does not equal functional dependence of tumor cells on IL-3 signaling and still requires validation through ligand stimulation, receptor blockade, and gene intervention.

5.2 Allergy and Eosinophilic Inflammation

(1) IL-5 drives eosinophil generation

IL-5 promotes bone marrow eosinophil differentiation and maintains eosinophils in the circulation and tissues.

(2) IL-3 enhances basophil responses

IL-3 increases basophil survival and degranulation sensitivity, amplifying the release of histamine, leukotrienes, and inflammatory cytokines.

(3) GM-CSF maintains tissue inflammation

GM-CSF can prolong the survival of tissue eosinophils and enhance inflammatory functions of macrophages and dendritic cells.

5.3 GM-CSF-Driven Autoimmune Inflammation

In rheumatoid arthritis, neuroinflammation, and some intestinal inflammatory conditions, activated T cells and tissue cells can produce GM-CSF. After acting on monocytes and macrophages, GM-CSF can enhance antigen presentation, inflammatory cytokine release, and tissue infiltration. Because GM-CSF also participates in host defense, tissue repair, and tissue-resident macrophage homeostasis, infection risk and tissue myeloid cell function should also be evaluated when blocking this pathway.

5.4 Insufficient GM-CSF Signaling and Pulmonary Alveolar Proteinosis

Insufficient GM-CSF signaling can lead to abnormal alveolar macrophage maturation and lipid metabolism, reducing pulmonary surfactant clearance capacity. Autoimmune pulmonary alveolar proteinosis is mainly associated with neutralizing anti-GM-CSF autoantibodies, whereas hereditary cases may involve functional abnormalities in CSF2RA or CSF2RB.

6 Targeted Intervention and Clinical Applications of βc Family Cytokines

6.1 Recombinant GM-CSF and Hematopoietic Recovery

Recombinant GM-CSF can promote survival, proliferation, and maturation of myeloid progenitors. It is used to support myeloid hematopoietic recovery after some chemotherapy or hematopoietic stem cell transplantation and can enhance mature myeloid cell functions. During application, excessive leukocyte increase, inflammatory responses, and responsiveness of underlying myeloid tumor cells to GM-CSF should be considered.

6.2 Targeting IL-5 and IL-5Rα

(1) Neutralizing IL-5

Neutralizing IL-5 reduces available IL-5 and inhibits eosinophil generation and survival.

(2) Targeting IL-5Rα

Targeting IL-5Rα blocks IL-5 receptor signaling or reduces IL-5Rα-positive eosinophils through effector mechanisms.

These strategies are mainly used for eosinophil-dominant asthma, vasculitis, and other eosinophil-related diseases.

6.3 CD123-Targeted Hematologic Tumor Therapy

CD123 can serve as a targeting marker for some myeloid tumor cells and blastic plasmacytoid dendritic cell neoplasms.

(1) Anti-CD123 monoclonal antibodies.

(2) Antibody-drug conjugates.

(3) Bispecific antibodies and T cell-engaging molecules.

(4) Chimeric antigen receptor T cells.

(5) Delivery of cytotoxic molecules using IL-3 receptor-binding structures.

6.4 Blockade of GM-CSF, GM-CSFRα, and the βc Chain

Anti-GM-CSF or anti-GM-CSFRα strategies can selectively inhibit GM-CSF-driven myeloid inflammation while preserving IL-3 and IL-5 signaling. Direct targeting of βc/CD131 can simultaneously affect GM-CSF, IL-3, and IL-5 signaling. This is suitable for studying pathological processes jointly maintained by multiple βc family cytokines, but it may also affect hematopoietic progenitors, eosinophils, and alveolar macrophage function.

7 Comparison of βc, gp130, and γc Shared Receptor Chain Systems

8 Products Related to βc Family Cytokines and Shared Receptor Research

The βc shared receptor system recognizes GM-CSF, IL-3, and IL-5 through ligand-specific α chains and integrates cell survival, proliferation, differentiation, and effector signals through CD131. Related research needs to distinguish single cytokine effects, specific α chain expression, and shared βc chain dependence. Receptor blockade, gene intervention, and detection of JAK2-STAT5, ERK, and AKT pathways should be combined to determine the specific roles of βc signaling in hematopoiesis, allergic inflammation, autoimmune diseases, and myeloid tumors.

For more related articles, please see below:

[1] Composition, Activation Mechanisms, and Biological Effects of the AKT Pathway

[2] Ras-Raf-MEK-ERK Signaling

[3] JAK-STAT Cell Signaling Pathway