IL 2 Human
Description
Molecular Structure and Receptor Interactions
IL-2 belongs to the four α-helix bundle cytokine family and signals through a heterotrimeric receptor (IL-2R) composed of α (CD25), β (CD122), and γ (CD132) subunits . Binding affinities vary:
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Low-affinity receptor (CD25 alone):
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Intermediate-affinity receptor (CD122/CD132):
The γ-chain is shared with receptors for IL-4, IL-7, IL-9, IL-15, and IL-21, enabling cross-regulation . Structural studies reveal that IL-2 binds CD25 at a central site, while CD122 and CD132 interact with helical regions .
Signaling Pathways and Gene Regulation
IL-2 activates three primary pathways:
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JAK-STAT: Phosphorylates STAT5, driving expression of CD25 and Prdm1 .
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PI3K/Akt/mTOR: Promotes cell survival and upregulates Bcl-6 .
Gene expression requires T cell receptor (TCR) activation and CD28 costimulation, activating transcription factors NFAT, AP-1, and NF-κB . Oct-1 enhances promoter activity in activated T cells .
Biological Functions
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T Cell Homeostasis: Drives proliferation of activated T cells and memory T cell differentiation .
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Regulatory T Cells (Tregs): Critical for Treg development and function, suppressing autoimmunity .
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NK and B Cells: Enhances cytotoxicity and antibody production .
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Immune Tolerance: Promotes activation-induced cell death (AICD) to prevent autoimmunity .
Autoimmune Diseases
Low-dose IL-2 (1–3 million IU/day) selectively expands Tregs, showing efficacy in:
Research Advances: Engineered IL-2 Variants
Mutant IL-2 proteins with reduced CD25 binding minimize toxicity and enhance antitumor activity:
Detection and Quantification
The Lumit® IL-2 Immunoassay enables rapid measurement in cell cultures :
| Parameter | Value |
|---|---|
| Limit of Detection (LOD) | 11.2 pg/mL |
| Dynamic Range | 28.2 pg/mL – 25 ng/mL |
| Assay Time | 70 minutes |
Evolutionary Conservation
IL-2 is conserved across jawed vertebrates, including fish and sharks . Fish IL-2 shares receptors with IL-15 but functions independently of co-presentation, unlike mammalian IL-15 . This evolutionary flexibility highlights its fundamental role in adaptive immunity .
Challenges and Future Directions
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Toxicity Management: Engineered IL-2 variants and fusion proteins aim to reduce vascular leak syndrome .
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Dual Immune Modulation: Balancing Treg expansion and effector T cell activation remains a therapeutic challenge .
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Broad Clinical Trials: Ongoing phase I/II trials explore IL-2 in rheumatoid arthritis, vasculitis, and sclerosing cholangitis .
Product Specs
T-cell growth factor (TCGF), Lymphokine, IL-2.
APTSSSTKK TQLQLEHLLL DLQMILNGIN NYKNPKLTRM LTFKFYMPKK ATELKHLQCL EEELKPLEEV LNLAQSKNFH LRPRDLISNI NVIVLELKGS ETTFMCEYAD ETATIVEFLN RWITFCQSII STLT.
Q&A
What is the structural basis for IL-2’s interaction with its receptors, and how does this influence receptor selectivity?
IL-2 binds to a trimeric receptor complex (CD25/CD122/CD132) with high-affinity (Kd ~10–100 pM) or a dimeric receptor (CD122/CD132) with intermediate affinity (Kd ~1–10 nM) . The α-subunit (CD25) is critical for high-affinity binding, while the β (CD122) and γ (CD132) subunits mediate signal transduction . Structural studies reveal that IL-2’s β-sheet structure enables conformational flexibility, allowing differential recruitment of receptor chains. This structural plasticity explains why Treg cells (rich in CD25) respond to low IL-2 concentrations, whereas effector T cells (CD122/CD132-only) require higher concentrations .
Methodological Insight: To study receptor selectivity, use flow cytometry to quantify CD25/CD122/CD132 expression on purified T cell subsets. Combine this with dose-response proliferation assays (e.g., CTLL-2 cells) to assess IL-2 potency in different receptor contexts .
How is IL-2 retained and released in human blood vessels, and what experimental models validate this process?
IL-2 is stored in blood vessels via binding to heparan sulfate proteoglycans (e.g., perlecan) on endothelial and smooth muscle cells . Release occurs enzymatically (heparanase) or mechanically (e.g., during leukocyte extravasation) .
Experimental Validation:
Contradiction Analysis: While systemic IL-2 contributes to vascular stores, local production by aortic T cells (GFP+ in IL-2 promoter-driven transgenic mice) also plays a role . This dual origin necessitates multi-tracer experiments (e.g., systemic vs. local IL-2 labeling) to disentangle sources.
What are the key challenges in engineering IL-2/antibody fusions for Treg-selective therapy, and how have recent studies addressed them?
Engineered IL-2/antibody fusions aim to amplify Treg responses while minimizing effector T cell activation. Challenges include:
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Half-life extension: Native IL-2 has a short plasma half-life (~15–30 minutes) .
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Receptor competition: Antibody binding may sterically hinder IL-2/receptor interactions .
Advanced Solutions:
Data Example: In ulcerative colitis models, covalent IL-2/antibody fusions increased Treg frequencies by 3–5 fold compared to free IL-2, with reduced neutrophil infiltration .
How do IL-2 knockout (KO) mice inform vascular and immune pathologies, and what experimental caveats exist?
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Autoimmune complications: Wild-type IL-2 KO mice exhibit lymphoproliferation and colitis, obscuring vascular-specific effects .
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Compensatory mechanisms: Other cytokines (e.g., IL-7, IL-15) may partially rescue T cell survival.
Optimized Models: Use DO11.10/RAG-1 KO/IL-2 KO mice (lacking endogenous T cells) to isolate vascular effects from immune-driven pathology . Histopathological scoring (e.g., smooth muscle cell density, elastic lamina integrity) should accompany functional assessments (e.g., blood pressure monitoring).
What are the metabolic and signaling pathways regulated by IL-2 in T cells, and how do they influence Treg/effector balance?
IL-2 activates JAK/STAT5 signaling, driving transcription of pro-survival genes (e.g., Bcl-2) and metabolic enzymes (e.g., PDK1, GLUT1) . Phosphoproteomic studies reveal IL-2 modulates >1,000 phosphosites, including kinases (e.g., mTOR, PI3K/Akt) and transcription factors (e.g., FoxO1) .
Methodological Approach:
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Metabolic profiling: Use 13C-labeled glucose/glutamine tracing to assess glycolysis/TCA cycle activity in IL-2-stimulated T cells .
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STAT5-specific inhibitors: Compare gene expression profiles (RNA-seq) with/without STAT5 activation to identify IL-2-dependent targets.
Contradiction: While IL-2 promotes Treg differentiation, chronic exposure can paradoxically activate effector T cells. This dichotomy may stem from differential STAT5 phosphorylation kinetics (sustained vs. transient) .
How can researchers resolve discrepancies between human and murine IL-2 biology in translational studies?
Key differences include:
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Receptor expression: Human Treg cells express higher CD25 levels than murine counterparts .
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IL-2 half-life: Human IL-2 has a longer half-life in circulation compared to murine IL-2 .
Solutions:
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Humanized mouse models: Transplant human T cells into immunodeficient mice to study IL-2 responses in a human receptor context .
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Species-specific bioassays: Validate IL-2/antibody fusions in humanized systems before clinical trials .
What emerging techniques enable single-cell resolution analysis of IL-2 responses in immune and vascular tissues?
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Spatial transcriptomics: Map IL-2 receptor expression in intact vascular tissues.
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Multimodal mass cytometry: Simultaneously profile IL-2-induced phosphoproteins, metabolites, and transcription factors in T cells.
Application: Combining scRNA-seq with CITE-seq can identify IL-2-responsive cell clusters in inflamed tissues, resolving heterogeneity in Treg/effector responses .
How do vascular IL-2 stores influence immune cell extravasation, and what experimental systems model this process?
IL-2 release during leukocyte transendothelial migration may prime T cells for activation. Experimental systems include:
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3D vascular organoids: Co-culture endothelial/smooth muscle cells with T cells to study IL-2 storage and release .
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Intravital microscopy: Track T cell interactions with IL-2-rich vascular surfaces in real time.
Data Gap: The role of heparanase from extravasating T cells vs. endothelial heparanase in IL-2 release remains unclear. Dual-inhibition approaches (anti-heparanase antibodies + endothelial-specific knockout) are needed .
What are the limitations of using IL-2-dependent cell lines (e.g., CTLL-2) to study IL-2 bioactivity, and how can they be mitigated?
CTLL-2 cells lack endogenous heparanase, requiring exogenous enzyme addition for IL-2 release assays . Limitations:
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Artificial conditions: Overexpression of heparanase may not mimic physiological release kinetics.
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Receptor bias: CTLL-2 cells may express atypical IL-2 receptor densities.
Improvements:
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Primary T cell bioassays: Use purified human T cells to assess IL-2 potency.
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Co-culture systems: Incorporate vascular endothelial cells to model physiological IL-2 presentation .
How do IL-2/antibody complexes compare to low-dose IL-2 for Treg expansion, and what clinical implications arise?
Clinical Relevance: IL-2/antibody fusions may enable once-weekly dosing in autoimmune diseases, improving patient compliance .
What are the unresolved questions in IL-2’s role in vascular biology, and how can they be addressed?
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Source specificity: Do systemic vs. locally produced IL-2 have distinct vascular effects?
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Cell-type targeting: Does IL-2 directly act on smooth muscle cells, or via secondary mediators?
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Therapeutic potential: Could IL-2 supplementation prevent aneurysms in IL-2-deficient patients?
Future Directions:
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Single-cell RNA-seq: Profile IL-2-responsive genes in vascular smooth muscle cells.
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Conditional knockouts: Target IL-2 deletion to specific vascular cell lineages.
Product Science Overview
IL-2 is best known for its role in inducing the proliferation of T-cells and natural killer (NK) cells . It also stimulates the growth and differentiation of B cells, lymphokine-activated killer cells, monocytes, macrophages, and oligodendrocytes . Additionally, IL-2 promotes the peripheral development of regulatory T cells (Treg cells), which are essential for maintaining immune tolerance .
The effects of IL-2 are mediated through a trimeric receptor complex consisting of IL-2Rα, IL-2Rβ, and the common gamma chain (γc) . Binding of IL-2 to its receptor initiates signaling cascades involving Jak1, Jak3, Stat5, and the PI3K/Akt pathways .
Recombinant human IL-2 has been used in various clinical settings, particularly in cancer immunotherapy. It has been employed to boost the immune response in patients with metastatic melanoma and renal cell carcinoma . The ability of IL-2 to activate and expand T-cells and NK cells makes it a valuable tool in adoptive cell transfer therapies.
IL-2 continues to be a subject of extensive research, with ongoing studies exploring its potential in treating autoimmune diseases, enhancing vaccine efficacy, and improving the outcomes of immunotherapy . Researchers are also investigating ways to modify IL-2 to reduce its toxicity and enhance its therapeutic benefits.
