Recombinant Human Interleukin-37 (IL37), partial (Active)

What is the molecular structure of IL-37 and how does it relate to function?

IL-37 belongs to the IL-1 family, with its coding gene located on the long arm of chromosome 2, positioned close to IL-1α and IL-1β genes. The protein has a unique structure with extended N and C termini that are disordered in the free protein state . Unlike other cytokines, IL-37 functions through a concentration-dependent mechanism where:

• Monomeric IL-37 is the active anti-inflammatory form

• At higher concentrations, IL-37 forms dimers with nanomolar affinity

• Dimerization occludes the activity of the IL-37 monomer

The presence of at least one extended terminus (either N or C) is required for IL-37's suppressive activity, though both termini appear unstructured in solution studies .

What are the main mechanisms of action for IL-37?

IL-37 possesses a unique "dual function" mechanism:

Extracellular mechanism:

• Binds to IL-18Rα and the decoy receptor IL-1R8 (SIGIRR)

• Forms a tripartite ligand-receptor complex

• Recombinant IL-37 induces a 16-fold increase in IL-1R8 mRNA levels in M1 macrophages

• Reduces TNF-α and IL-6 expression by 50-55% in LPS-stimulated mouse bone marrow-derived dendritic cells (absent in IL-1R8-deficient mice)

Intracellular mechanism:

• Interacts with SMAD3

• Translocates to the nucleus

• Induces anti-inflammatory effects through nucleus-targeting sequences

• Mutant IL-37D20A (lacking nucleus-targeting sequences) shows impaired anti-inflammatory activity

Both mechanisms contribute to suppressing pro-inflammatory cytokine production, including IL-1A, IL-6, CCL12, CSF1, CSF2, CXCL13, IL-1B, IL-23A, and IL-1RN .

How is recombinant IL-37 produced and what is its typical composition?

Commercially available recombinant human IL-37:

• Typically expressed in Escherichia coli

• Represents a fragment spanning amino acids 27-192

• Contains >95% pure protein with <1 EU/μg endotoxin level

• Sequence contains: KNLNPKKFSIHDQDHKVLVLDSGNIAVPDKNYIRPEIFFALASSLSSASAEKGSPILLGVSKGEFCLYCDKDKGQSHPSLQLKKEKLMKLAAQKESARRPFIFYRAQVGSWNMLESAAHPGWFICTSCNCNEPVGVTDKFENRKHIEFSFQPVCKAEMSPSEVSDK

What are optimal dosing protocols for recombinant IL-37 in animal models?

Research indicates different effective dosing strategies depending on the model:

For acute inflammation models:

• Pretreatment with 300 ng recombinant IL-37 per animal (i.p.) for 3 consecutive days before inflammatory challenge

• This regimen has shown efficacy in protecting against IL-1β-induced cognitive deficits in Y-Maze behavioral tests

For disease-specific models:

• In experimental autoimmune encephalomyelitis (EAE), multiple application protocols have been tested using various forms of recombinant human IL-37

• For cardiovascular studies, recombinant IL-37 has demonstrated protection against atherosclerosis in ApoE-deficient models

When designing experiments, consider that native IL-37 at 2.5 nM reduces LPS-induced VCAM protein levels by ~50%, while the monomeric D73K mutant achieves 90% reduction at the same concentration .

How can researchers ensure optimal activity of recombinant IL-37 in cellular assays?

Several factors influence IL-37 activity in experimental settings:

Concentration considerations:

• Lower concentrations are often more effective than higher concentrations

• Higher IL-37 concentrations promote dimerization, reducing anti-inflammatory activity

• Native IL-37 forms dimers with nanomolar affinity

Experimental conditions:

• IL-37 is a heparin-binding protein, which modulates its self-association

• Consider including appropriate controls:

  • IL-37D20A mutant (lacking nucleus-targeting sequences) as negative control for intracellular effects

  • Tests in IL-1R8-deficient cells to control for receptor-mediated effects

Timing considerations:

• For optimal suppression of inflammatory responses, pretreatment with IL-37 before inflammatory stimulus is recommended

• Effects can be measured through reduced production of ICAM-1, VCAM-1, pro-inflammatory cytokines, and NF-κB pathway activation

How does IL-37 modulate neuroinflammation and neuronal function?

IL-37 shows significant neuroprotective effects through multiple mechanisms:

Acute neuroinflammation:

• Prevents LPS-induced microglial activation

• Preserves dendritic spine density after inflammatory challenge

• Maintains long-term potentiation (LTP) that would otherwise be impaired by inflammation

• Reduces inflammatory cytokine production in the CNS

Chronic neurodegeneration models:

• In APP/PS1 Alzheimer's disease models, IL-37 expression improves:

  • Spatial memory in Morris water maze tests

  • Reference memory in probe trials

  • Learning capacity during acquisition phase

• IL-37 transgenic expression in AD models shows preservation of cognitive abilities compared to APP/PS1 mice without IL-37

These findings suggest IL-37 as a potential therapeutic candidate for both acute and chronic neuroinflammatory conditions.

What are the effects of IL-37 on cellular signaling pathways?

IL-37 modulates several key inflammatory signaling cascades:

PKR-NF-κB pathway:

• Recombinant IL-37 suppresses PKR and NF-κB activation induced by soluble ECM proteins (matrilin-2 or biglycan)

• Inhibits downstream production of ICAM-1 and VCAM-1

Intracellular signaling:

• Nuclear translocation with SMAD3 is critical for intracellular anti-inflammatory effects

• IL-37D20A mutant (lacking nuclear localization sequence) fails to suppress inflammation

Extracellular receptor-mediated signaling:

• Forms tripartite complex with IL-18Rα and IL-1R8

• IL-1R8 is essential for anti-inflammatory effects (effects absent in IL-1R8-deficient models)

Understanding these pathways helps researchers design targeted experiments to dissect IL-37's mechanisms in specific disease contexts.

How can IL-37 be combined with cell-based therapies?

Research has demonstrated synergistic effects when combining IL-37 with cellular therapies:

Mesenchymal stem cells (MSCs) and IL-37:

• MSCs overexpressing IL-37 maintain their stem cell characteristics

• Enhanced immunosuppressive properties:

  • Increased inhibition of splenocyte proliferation

  • Greater reduction in pro-inflammatory factors (IL-1, TNF-α, IL-17, IL-6)

  • Stronger inhibition of autoantibodies (anti-dsDNA and anti-ANA)

In vivo application:

• MSCs overexpressing IL-37 injected into MRL/lpr mice (SLE model) showed:

  • Better survival rates

  • Reduced SLE symptoms

  • Decreased pro-inflammatory factors

  • Lower antibody and autoantibody levels

  • Reduced T cell numbers in serum and kidneys compared to control MSCs or IL-37 alone

This mutually reinforcing relationship occurs because:

• IL-37 expression by MSCs maintains high serum IL-37 levels

• IL-37 inhibits inflammation, creating a more favorable environment for MSC survival

• Enhanced survival of transplanted MSCs prolongs therapeutic effects

What experimental models are most appropriate for studying IL-37 function?

Multiple experimental systems have been validated for IL-37 research:

Transgenic mouse models:

• hIL-37tg mice (expressing human IL-37b)

• IL-1R8 KO mice (to study receptor dependency)

• hIL-37tg-IL-1R8 KO double transgenic mice (to distinguish intracellular from receptor-mediated effects)

• APP/PS1-IL-37tg mice (for Alzheimer's disease studies)

Disease-specific models:

• Experimental autoimmune encephalomyelitis (EAE) for Multiple Sclerosis

• APP/PS1 transgenic mice for Alzheimer's disease

• MRL/lpr mice for Systemic Lupus Erythematosus

• ApoE-deficient models for atherosclerosis

Cellular models:

• Aortic valve interstitial cells (AVICs) for studying valve inflammation

• Bone marrow-derived dendritic cells

• M1 macrophages

• Mesenchymal stem cells

How can researchers reliably measure the anti-inflammatory effects of IL-37?

Several validated endpoints can quantify IL-37's anti-inflammatory activity:

Protein expression markers:

• Reduced ICAM-1 and VCAM-1 expression

• Decreased pro-inflammatory cytokines (IL-1, TNF-α, IL-6, IL-17)

• Inhibition of PKR and NF-κB activation

Functional assays:

• Inhibition of dendritic cell maturation

• Reduced T cell proliferation

• Decreased autoantibody production in autoimmune models

Neurological assessments:

• Preservation of long-term potentiation (LTP)

• Maintenance of dendritic spine density

• Improved cognitive performance in behavioral tests:

  • Y-Maze for short-term memory

  • Morris water maze for spatial learning and memory

What are the key considerations when comparing native IL-37 versus engineered variants?

When designing experiments with IL-37 variants:

Structural modifications:

• Point mutations at the IL-37 dimer interface (e.g., D73K mutant) create stable monomers with enhanced anti-inflammatory activity

• IL-37D20A mutant lacking nucleus-targeting sequences has impaired intracellular activity

• N and C terminal modifications can affect function, as at least one extended terminus is necessary for activity

Functionality comparison:

• Monomeric IL-37 forms provide greater suppression of inflammatory cytokines compared to native IL-37

• Native IL-37 at 2.5 nM reduces LPS-induced VCAM by ~50%, while the D73K monomeric mutant achieves 90% reduction

• High concentrations of native IL-37 show reduced efficacy due to dimer formation

Experimental controls:

• Include both wild-type IL-37 and relevant mutants

• Consider testing across multiple cell types, as effects may vary

• Use receptor knockout models (IL-1R8 KO) to distinguish receptor-dependent from intracellular effects

What are the current research hotspots in IL-37 biology?

Bibliometric analysis reveals several emerging research directions:

Disease applications:

• Keyword analysis shows "inflammation," "dendritic cell," "rheumatoid arthritis," "pathogenesis," and "disease" as high-frequency terms

• Citation burst analysis identifies "suppression" as a current research front

• Emerging evidence for IL-37's role in various disorders represents a significant hotspot

Mechanistic investigations:

• Further elucidation of IL-37's immunomodulatory mechanisms

• Understanding the molecular basis for IL-37's picomolar activity despite weak interaction with IL-18Rα

• Exploring additional mediators of IL-37 activity and potential multiple cell surface interactions

Research categories:

• Immunology and Cell Biology account for approximately 50% of IL-37 publications

• Biochemistry/Molecular Biology (16.85%) and Medicine Research Experimental (9.74%) are also significant fields

• The immunomodulatory effect of IL-37 and its role in different cells remain major research foci

How does IL-37 research inform development of novel anti-inflammatory therapeutics?

IL-37 offers several unique properties that inform therapeutic development:

Mechanistic insights:

• Dual mechanism (intracellular and extracellular) provides multiple potential drug targets

• Concentration-dependent efficacy (with lower concentrations being more effective) informs dosing strategies

• Monomer vs. dimer activity suggests structural modifications for enhanced efficacy

Therapeutic applications:

• Demonstrated efficacy in multiple disease models suggests broad therapeutic potential

• Protection against neuroinflammation in both acute and chronic settings

• Synergistic effects with cell-based therapies like MSCs offer combination approaches

Development considerations:

• Engineering stable monomeric forms may enhance anti-inflammatory activity

• Understanding heparin binding and other interactions could improve pharmacokinetics

• The requirement for extended termini despite their disorder suggests functional regions for therapeutic targeting

These insights can guide the development of IL-37-based therapeutics or small molecules that mimic its anti-inflammatory effects.

What are common technical issues when working with recombinant IL-37?

Researchers should be aware of several technical considerations:

Activity assessment challenges:

Experimental variability factors:

• Endotoxin contamination can confound inflammatory studies

• Heparin binding may affect IL-37 behavior in various buffers or media

• Potential species-specific differences (IL-37 is not naturally expressed in mice)

Solutions:

• Use low endotoxin preparations (<1 EU/μg)

• Test multiple concentrations to identify optimal dosing

• Include appropriate genetic controls (receptor knockouts, nuclear localization mutants)

• Consider both in vitro pretreatment and in vivo multiple dosing strategies