Recombinant Human IL-37 Mechanism in Endometriosis Treatment

Research Article Overview: Recombinant Human IL-37 Inhibits Endometriosis

Introduction to Endometriosis and IL-37

  • Endometriosis (EMs): A common gynecological disease characterized by activated endometrial cells planting outside the endometrium.
    • Incidence: Affects approximately 10% to 15%10\% \text{ to } 15\% of women of childbearing age.
    • High Incidence in Specific Cases: Up to 30%30\% in patients with infertility or chronic pelvic pain.
    • Consequences: Endometriosis has serious reproductive and general health implications.
    • Risk: Patients with endometriosis have a higher risk of developing ovarian cancer.
    • Current Treatment Landscape: Goals include reducing operative intervention, preserving fertility, preventing recurrence, improving quality of life, and pain control. However, despite drugs like GnRH antagonists, aromatase inhibitors, and antiprogestins, treatment remains a significant challenge, necessitating new pathogenic insights and therapeutic strategies.
  • Inflammatory Nature and Immune Dysfunction in Endometriosis:
    • Chronic and Inflammatory Disease: Endometriosis is well-known as such.
    • Pro-inflammatory Cytokines: High concentrations of Tumor Necrosis Factor-$\alpha$ (TNF-$\alpha$) are found in the peritoneal fluid of patients.
    • Abnormal Immune System: Directly linked to endometriosis development, showing an obvious increase in immune cells in serum and peritoneal fluid.
    • T Helper (Th) Cell Imbalance: Th1 and Th2 cell proportions are imbalanced in patient serum.
      • Th1-related Cytokines: Low expression of Interferon-$\gamma$ (IFN-$\gamma$).
      • Th2-related Cytokines: High expression of Interleukins (IL)-4, IL-10, and IL-13.
  • Crucial Role of Dendritic Cells (DCs): DCs are specialized immune cells involved in both innate and adaptive T cell-mediated immunological responses.
    • DC Maturation Status in Endometriosis: The number of immature dendritic cells (iDCs) is notably higher than mature dendritic cells (mDCs) in endometriosis tissues from non-human primate models.
    • Previous Findings: Immature bone marrow-derived DCs, not mature ones, contribute to endometriosis development, suggesting a critical role for mDCs in improving the disease outcome.
  • Interleukin-37 (IL-37): A unique IL-1 family member, acting as a natural suppressor of inflammation.
    • Protective Functions: Plays a protective role in various diseases, including colitis, arthritis, sepsis, and endotoxin shock.
    • Mechanisms of Action: IL-37 can suppress the production of pro-inflammatory cytokines (e.g., IL-1$\beta$, IL-6, and IL-10) and inhibit endometriosis development by targeting multiple signaling pathways (e.g., mitogen-activated protein kinase signaling and Wnt/$\beta$-catenin).
    • Specific Variant Action: The IL-37b splice variant has been shown to suppress lesion growth in endometriotic mouse models by regulating invasion, angiogenesis, proliferation, and inflammation via AKT and ERK1/2 signaling pathways.
    • Knowledge Gap: The specific effect of IL-37 on abnormal immune cells, particularly T helper cells and dendritic cells, in endometriosis was previously unclear.
  • Study Hypothesis: This study investigates whether recombinant human IL-37 (rhIL-37) can inhibit endometriosis development by increasing the Th1/Th2 ratio, specifically through inducing the maturation of DCs and inhibiting IL-4 production via suppressing STAT3 phosphorylation.

Materials and Methods

  • Reagents:
    • Mice: Female C57BL/6 mice (6−86-8 weeks old; 19−2419-24 g) from Jiangsu Ailingfei Biotechnology Co., Ltd.
    • rhIL-37: Obtained from Abcam (ab151873, USA).
    • Other Key Reagents: Estradiol benzoate (E8875-250MG), Lipopolysaccharide (LPS, SMB00704), IL-4 (SRP3093) from Sigma-Aldrich; Colivelin (STAT3 activator, CAS 867021-83-8) from Santa Cruz Biotechnology, Inc.
    • Antibodies for Flow Cytometry: FITC-labeled anti-CD4, APC-labeled anti-CD11c, APC-labeled anti-IFN-$\gamma$, PE-labeled anti-IL-4, PE-labeled anti-CCR5, PE-labeled anti-CD83, Biotin-labeled anti-MHC II, FITC-labeled anti-CD40, PE-labeled anti-CD80, APC-labeled anti-CD86 (all from eBioscience, California, USA).
    • Cell Culture Components: RPMI-1640 medium, fetal bovine serum, penicillin-streptomycin sulfate (Gibco, USA).
    • Co-culture System: Transwell-6 system with a 0.4μm0.4 \mu\text{m} porous membrane (Corning, NY, USA).
    • ELISA Kits: Mouse IL-37, IFN-$\gamma$, TNF-$\alpha$, IL-4, and IL-13 ELISA kits (Shanghai Enzyme-linked Biotechnology Co., Ltd.).
    • Molecular Biology Reagents: TRIzol reagent (Invitrogen), Transcriptor First Strand cDNA Synthesis Kit (Roche), SYBR Premix Ex Taq (Takara).
    • Western Blotting Reagents: RIPA lysis buffer, BCA Protein Assay Reagent Kit, enhanced chemiluminescence kit (Solarbio), anti-STAT3 (ab68153), anti-p-STAT3 (ab267373) primary antibodies, and goat anti-rabbit (ab6721) secondary antibody (all from Abcam).
  • Establishment of Endometriosis Mouse Model:
    • Environmental Control: Mice housed under standard conditions: 60−70%60-70\% relative humidity, 22−24∘C22-24 ^{\circ}\text{C} temperature, and a 12 h12 \text{ h} light/12 h12 \text{ h} dark cycle.
    • Donor Uteri Preparation: After 11 week of adaptation, donor mice were subcutaneously injected with 3μg3 \mu\text{g} of estradiol benzoate dissolved in 50μl50 \mu\text{l} of soybean oil.
    • Endometrial Tissue Collection: One week post-injection, uteri were dissected, and endometrial tissues were carefully obtained. These were cut into pieces smaller than 1 mm31 \text{ mm}^3 and suspended in 1 ml1 \text{ ml} normal saline per mouse.
    • Recipient Implantation: Each recipient mouse received 500μl500 \mu\text{l} of the tissue suspension.
    • Ethical Oversight: All animal experiments adhered strictly to ethical guidelines and regulations, approved by the ethical committee of the Third Xiangya Hospital of Central South University (No. 2018-S146).
  • Isolation of CD4+T Cells and DCs, Cell Culture, and Treatment:
    • Cell Acquisition: Peritoneal lavage fluid samples were collected from healthy mice and mice with endometriosis via peritoneal lavage with 5 ml5 \text{ ml} ice-cold PBS, then centrifuged at 1500 g1500 \text{ g} for 55 min.
    • Cell Staining for Sorting: Cells were resuspended in PBS and stained with FITC-labeled anti-CD4 (for CD4+T cells) or APC-labeled anti-CD11c (for DCs) antibodies for 3030 min at 4∘C4 ^{\circ}\text{C} in the dark.
    • Flow Cytometric Separation: A FACSVerse (BD) flow cytometer was used to isolate CD4+T cells from healthy mice and DCs from healthy (control-DCs) and endometriotic (EMs-DCs) mice.
    • Cell Culture Conditions:
      • CD4+T cells: Cultured in RPMI-1640 medium supplemented with 10%10\% fetal bovine serum, 100 U/mL100 \text{ U/mL} penicillin, and 100μg/mL100 \mu\text{g/mL} streptomycin sulfate.
      • DCs: Cultured in RPMI-1640 medium supplemented with 10%10\% fetal bovine serum, 100 U/mL100 \text{ U/mL} penicillin, 100μg/mL100 \mu\text{g/mL} streptomycin sulfate, 10 ng/ml10 \text{ ng/ml} IL-4, and 20 ng/ml20 \text{ ng/ml} recombinant mouse GM-CSF.
      • All cells were maintained at 37∘C37 ^{\circ}\text{C} in a humidified atmosphere with 5%5\% CO$_2$.
    • Specific Cell Treatments:
      • rhIL-37: Used at 100 ng/mL100 \text{ ng/mL} for DCs stimulation.
      • LPS: Used at 100 ng/mL100 \text{ ng/mL} to induce the maturation of iDCs.
      • IL-4: Used at 100 ng/mL100 \text{ ng/mL} to stimulate DCs.
      • Colivelin: Used at 0.5μM0.5 \mu\text{M} as a STAT3 activator.
  • Administration of rhIL-37 to Mice for in vivo Experiments:
    • Group Assignment: Endometriosis mouse models were randomly divided into three groups: EMs (n=6n=6), EMs + NS (n=12n=12), and EMs + rhIL-37 (n=12n=12).
    • Control: C57BL/6 mice in a control group underwent acupuncture but received no injections.
    • Treatment Protocol:
      • EMs + NS group: Intraperitoneally injected with normal saline.
      • EMs + rhIL-37 group: Intraperitoneally injected with 1000 ng1000 \text{ ng} of rhIL-37 (dissolved in normal saline).
      • Administration: Initiated 24 h24 \text{ h} before modeling, then performed once every 22 days for a total of 1010 times.
    • Sample Collection: At 24 h24 \text{ h} after the last injection, all mice were sacrificed by cervical dislocation. Ectopic lesions were observed, weighed, and their volume evaluated. Peripheral blood samples were also collected.
  • Detection of IL-37, IFN-$\gamma$, TNF-$\alpha$, IL-4, and IL-13 by ELISA Assay:
    • Measurements: Concentrations of these cytokines in serum and the production of IL-4 in DCs were measured.
    • Procedure: Experiments were conducted according to manufacturer’s instructions. Optical density (OD) values at 450 nm450 \text{ nm} were examined using a microplate reader (BioRad Model 680).
  • Analysis of Th1/Th2 Cells Ratio, iDCs and mDCs Percentages, and Surface Marker Expression on DCs by Flow Cytometry:
    • Th1/Th2 and Th1/Th2 Ratio: CD4+T cells were stained with APC-labeled anti-IFN-$\gamma$ (for IFN-$ \gamma $ + T cells, Th1 cells) and PE-labeled anti-IL-4 (for IL-4+T cells, Th2 cells) to detect differentiation.
    • DCs Maturation: DCs were stained with APC-labeled anti-CD11c and PE-labeled anti-CCR5 (for CD11c+CCR5+DCs, iDCs), or APC-labeled anti-CD11c and PE-labeled anti-CD83 (for CD11c+CD83+DCs, mDCs).
    • DCs Surface Markers: DCs were stained with PE-labeled anti-MHC II, FITC-labeled anti-CD40, PE-labeled anti-CD80, and APC-labeled anti-CD86.
    • Staining Protocol: Cells were incubated with antibodies in the dark for 3030 min at 4∘C4 ^{\circ}\text{C}.
    • Data Analysis: Percentages of Th1, Th2, iDCs, mDCs, and positive cells for CD40, CD80, CD86, and MHC II were analyzed using a FACS Aria (BD) flow cytometer with Flow Jo v10.0.7 software.
  • Co-Culture System of CD4+T Cells and DCs:
    • Setup: A Transwell system was used, with CD4+T cells in the upper chamber and DCs in the bottom chamber.
    • Treatment During Co-culture: CD4+T cells were co-treated with LPS, rhIL-37, and IL-4 for 24 \text{ h}$.
    • Evaluation: DCs maturation, Th1/Th2 cell ratio, and expression of specific molecules were measured post-co-culture.
  • Measurement of Gene Expression by qRT-PCR:
    • Targets: mRNA expression levels of IFN-$\gamma$, TNF-$\alpha$, IL-4, and IL-13 were measured.
    • RNA Isolation: Total RNA was extracted from CD4+T cells using TRIzol reagent.
    • Reverse Transcription: RNA was reverse-transcribed into cDNA using the Transcriptor First Strand cDNA Synthesis Kit.
    • Real-time PCR: Performed on an ABI 7500 Real-time PCR system (Applied Biosystems) using SYBR Premix Ex Taq.
    • Quantification: Relative expression levels were normalized to GAPDH and calculated using the 2^{-\Delta\Delta\text{Ct}} method.
    • Primer Sequences: Forward (F) and Reverse (R) primers were provided for IFN-$\gamma$, TNF-$\alpha$, IL-4, IL-13, and GAPDH.
  • Detection of STAT3 and its Phosphorylation by Western Blotting Assay:
    • Protein Extraction: Total protein was isolated from DCs using RIPA lysis buffer.
    • Protein Quantification: Protein concentration was determined using a BCA Protein Assay Reagent Kit.
    • Electrophoresis and Transfer: 25 \mu\text{g}ofproteinwasseparatedonaof protein was separated on a12\%SDS−PAGEgelandtransferredontoPVDFmembranes.</li><li><strong>Immunoblotting:</strong>MembraneswereblockedwithSDS-PAGE gel and transferred onto PVDF membranes.</li> <li><strong>Immunoblotting:</strong> Membranes were blocked with5\%non−fatmilkfornon-fat milk for1 \text{ h}atroomtemperature,thenincubatedovernightatat room temperature, then incubated overnight at4 ^{\circ}\text{C}withanti−STAT3andanti−p−STAT3primaryantibodies.</li><li><strong>SecondaryAntibody:</strong>Membraneswerethenincubatedwithasecondarygoatanti−rabbitantibodyforwith anti-STAT3 and anti-p-STAT3 primary antibodies.</li> <li><strong>Secondary Antibody:</strong> Membranes were then incubated with a secondary goat anti-rabbit antibody for1 \text{ h} at room temperature.
    • Detection and Analysis: An enhanced chemiluminescence kit was used to visualize protein bands. Optical density of the bands was analyzed using Image-Pro Plus 6.0 software. Relative expression was normalized to $\beta$-actin.
  • Statistical Analysis:
    • Software: SPSS 19.0 (SPSS Inc., USA).
    • Data Representation: All data were presented as mean $\pm$ standard deviation (SD).
    • Group Comparisons:
      • Among multiple groups: One-way analysis of variance (ANOVA) followed by Bonferroni’s test.
      • Between two independent groups: Student’s t-test.
    • Significance: A P-value lower than 0.05((P < 0.05) was considered statistically significant.
    • Replication: All experiments were independently repeated at least three times.

Results

rhIL-37 Inhibited Lesion Development, Increased Serum Th1/Th2 Ratio, and Induced DCs Maturation in Endometriosis Mice
  • Inhibition of Ectopic Lesion Development:
    • Compared to untreated or normal saline-treated endometriosis mice, rhIL-37 treatment significantly decreased the weight and volume of ectopic lesions (Fig. 1A-C).
    • This demonstrates the effective inhibitory effect of rhIL-37 on endometriosis development.
  • Serum IL-37 Levels:
    • rhIL-37 was highly present in the serum of rhIL-37-treated mice.
    • No rhIL-37 was detected in the serum of control, EMs, or EMs + NS groups (Fig. 1D).
  • Serum Cytokine Concentrations:
    • IFN-$\gamma$: No significant difference in serum levels observed across all groups (Fig. 1E).
    • TNF-$\alpha$: Significantly upregulated (pro-inflammatory) in endometriosis mice, but partially downregulated by rhIL-37 treatment (Fig. 1F).
    • IL-4 and IL-13: Upregulated in endometriosis mice, but rhIL-37 treatment effectively reduced their levels (Fig. 1G and H).
    • Interpretation: These findings suggest rhIL-37's role in regulating Th1 and Th2 differentiation, which are critical for these cytokines.
  • Th1/Th2 Cell Proportions in Blood:
    • Th1 Cells: No significant difference in percentage.
    • Th2 Cells: Significantly upregulated in mice with endometriosis.
    • Th1/Th2 Ratio: Downregulated in mice with endometriosis. rhIL-37 treatment partly rescued both the Th2 upregulation and the Th1/Th2 ratio downregulation (Fig. 2A-C).
  • DCs Maturation Markers in Blood:
    • CD40-positive and CD86-positive DCs: Percentages declined in endometriosis mice but increased with rhIL-37 treatment (Fig. 2D-E, Supplementary Fig. 1).
    • CD80-positive and MHC II-positive DCs: No significant difference in percentages observed (Fig. 2F-G, Supplementary Fig. 1).
    • Summary: The overall data indicated that rhIL-37 induced DCs maturation, increased Th1/Th2 percentages, and improved endometriosis conditions in vivo.
rhIL-37 Upregulated Th1/Th2 Ratio Through Inducing DCs to Mature
  • rhIL-37's Effect on DCs Maturation in vitro:
    • Cell Isolation Confirmation: CD4+T cells were successfully isolated from healthy mice (Supplementary Fig. 2), and DCs from healthy (control-DCs) and endometriosis (EMs-DCs) mice (Supplementary Fig. 3).
    • Treatment: Control-DCs and EMs-DCs were treated with 100 \text{ ng/mL}rhIL−37forrhIL-37 for24 \text{ h}$.
    • iDC and mDC Percentages:
      • rhIL-37 treatment decreased the percentage of iDCs in both control-DCs and EMs-DCs. EMs-DCs showed a higher initial iDC percentage than control-DCs (Fig. 3A and B).
      • Conversely, rhIL-37 treatment promoted the maturation of DCs (increased mDC percentage) in both groups, reversing the lower mDC percentage observed in EMs-DCs compared to control-DCs (Fig. 3C and D, Supplementary Fig. 4).
    • DCs Surface Maturation Markers (post-LPS stimulation):
      • LPS stimulation was applied for an additional 22 days to rhIL-37-treated DCs.
      • EMs-DCs exhibited significantly lower percentages of CD40-, CD80-, CD86-, and MHC II-positive DCs compared to control-DCs.
      • Crucially, rhIL-37 treatment increased the percentages of all these maturation markers in both control-DCs and EMs-DCs (Fig. 3E-H, Supplementary Fig. 5).
    • Conclusion: These results confirm that rhIL-37 actively contributes to the maturation of DCs.
  • Co-culture System of DCs with CD4+T Cells:
    • Experimental Setup: CD4+T cells were co-cultured with control-DCs, EMs-DCs, rhIL-37-treated control-DCs, rhIL-37-treated EMs-DCs, and LPS-treated DCs.
    • Th1 Differentiation: All DCs, regardless of origin or treatment, promoted Th1 differentiation, indicating a general function of DCs in this process (Fig. 4A).
    • Th2 Differentiation and Th1/Th2 Ratio:
      • EMs-DCs significantly promoted Th2 differentiation and downregulated the Th1/Th2 ratio compared to control-DCs.
      • rhIL-37 treatment partly reversed these effects, inhibiting Th2 differentiation and increasing the Th1/Th2 ratio (Fig. 4B-C).
    • mRNA Expression in Co-cultured CD4+T Cells:
      • The expression of IFN-$\gamma$, TNF-$\alpha$, IL-4, and IL-13 mRNAs was facilitated in CD4+T cells co-cultured with DCs.
      • EMs-DCs boosted the expression of TNF-$\alpha$, IL-4, and IL-13 mRNAs in CD4+T cells.
      • Significantly, rhIL-37 and LPS treatment notably inhibited the expression of TNF-$\alpha$, IL-4, and IL-13 mRNAs (Fig. 4D-G).
    • Overall Finding: rhIL-37 inhibited Th2 differentiation and increased the Th1/Th2 ratio by inducing DCs to mature.
rhIL-37 Upregulated Th1/Th2 Ratio by Suppressing the Production of IL-4 in DCs
  • Direct Inhibition of IL-4 by rhIL-37:
    • rhIL-37 stimulation significantly suppressed the production of IL-4 in control-DCs (Fig. 5A).
  • IL-4's Role in Th2 Differentiation:
    • To investigate if rhIL-37-treated DCs increase the Th1/Th2 ratio by regulating IL-4, control-DCs and EMs-DCs were treated with IL-4 combined with rhIL-37.
    • Flow cytometry revealed that the Th1/Th2 ratio was significantly lower in CD4+T cells co-cultured with EMs-DCs compared to those co-cultured with control-DCs (Fig. 5B and C).
    • In CD4+T cells co-cultured with EMs-DCs:
      • The proportion of Th1 cells and expression of TNF-$\alpha$ decreased.
      • The proportion of Th2 cells and expression of IL-4 and IL-13 increased (Fig. 5D and E).
    • Conclusion: rhIL-37 increased the Th1/Th2 ratio by inhibiting the production of IL-4 in DCs, underscoring IL-4's role as a key factor mediating Th2 differentiation stimulated by DCs.
rhIL-37 Promoted DCs Maturation by Inhibiting STAT3 Phosphorylation
  • STAT3 Phosphorylation Inhibition:
    • rhIL-37 treatment notably downregulated the phosphorylation level of STAT3 in control-DCs (Fig. 6A and B).
  • Reversal by STAT3 Activator (Colivelin):
    • In experiments where control-DCs were pre-treated with Colivelin (a STAT3 activator) before rhIL-37 treatment and co-culture with CD4+T cells:
      • Colivelin pre-treatment significantly upregulated the percentage of iDCs and downregulated the percentage of mDCs (Fig. 6C-E).
      • Crucially, Colivelin reversed the rhIL-37-induced downregulation of iDCs and upregulation of mDCs, effectively negating rhIL-37's pro-maturation effect.
    • Effect on Surface Maturation Markers: Colivelin treatment effectively downregulated the percentages of CD40-, CD80-, CD86-, and MHC II-positive DCs (Fig. 7A-D, Supplementary Fig. 6).
    • The rhIL-37-induced upregulation in these markers was also reversed by STAT3 phosphorylation activation with Colivelin.
  • Conclusion: rhIL-37 induced DCs to mature through inhibiting the phosphorylation of STAT3, indicating that STAT3 signaling is a critical downstream target of rhIL-37 in DC biology.

Discussion

  • IL-37 as an Anti-inflammatory Agent: IL-37 is widely expressed in various human tissues and immune cells (e.g., circulating monocytes, tissue macrophages, DCs, tonsillar B cells, plasma cells), confirming its role as an anti-inflammatory cytokine in numerous inflammatory disorders, including endometriosis.
  • Confirmation of rhIL-37's Efficacy: This study provides strong evidence that rhIL-37 treatment significantly inhibits the development of ectopic lesions in mouse models of endometriosis.
  • Complex Role of IL-37 on DCs Maturation:
    • Conflicting Previous Literature: Some research indicates IL-37 promotes DC recruitment and activation (e.g., in hepatocellular carcinoma), while other studies suggest it suppresses DC maturation via the IL-1R8/Toll-like receptor 4/NF-$\kappa$B pathway.
    • This Study's Contribution: The current findings clarify that rhIL-37 actively promotes DC maturation in the context of endometriosis, as evidenced by increased proportions of CD40-, CD80-, CD86-, and MHC II-positive DCs.
  • rhIL-37's Specific Impact on Th Cell Differentiation:
    • Previous Research: IL-37 has been shown to inhibit Th2 and Th17 differentiation and suppress effector cytokines (like IL-4, IL-5, IL-6) but shows no significant effect on Th1 and Treg cells or IFN-$\gamma$ and IL-10 expression.
    • Alignment with Current Study: This study's results are consistent, demonstrating that rhIL-37 has no effect on Th1 differentiation but inhibits Th2 differentiation in the endometriosis mouse model.
    • Key Mechanism Elucidated: The study importantly reveals that rhIL-37 increases the Th1/Th2 ratio by inducing the maturation of DCs, thereby linking DC maturation to the modulation of Th cell balance.
  • Endometriosis and Immune Cell Significance:
    • As a chronic pro-inflammatory disease, immune cells (T cells, NK cells) and pro-inflammatory factors create suitable conditions for ectopic endometrial cell survival and growth.
    • T Cell Importance: T cell-deficient mice can be used to establish endometriosis models without additional B cell clearance, highlighting the critical role of T cells.
    • Dynamic T Cell Changes: Early endometriosis is associated with increased T cell numbers in peritoneal fluid, followed by increasing T cell apoptosis as the disease progresses.
    • Th1/Th2 Imbalance in Endometriosis Tissues: Endometriosis tissues exhibit lower percentages of Th1 cells and related cytokines, alongside higher Th2-related cytokine levels, compared to normal endometrial tissues.
  • Role of IL-4 in Th2 Differentiation:
    • Since rhIL-37 does not affect Th1 differentiation, the study focused on the pathway for inhibiting Th2 differentiation.
    • IL-4 is a crucial inducer of Th2 cells.
    • This study identified a direct inhibitory effect of rhIL-37 on IL-4 expression in DCs.
    • Mechanism Confirmation: It was definitively proven that rhIL-37 increases the Th1/Th2 ratio through inhibiting IL-4 production in DCs.
  • STAT3's Role in DCs Maturation in Endometriosis:
    • STAT3 Hyperactivation: Known to cause autoimmunity and immunodeficiency by regulating immune cells and can suppress the maturation of bone marrow-derived DCs in tumors.
    • Relevance to Endometriosis: STAT3 phosphorylation levels are significantly elevated in endometriosis tissues compared to normal endometrial tissues.
    • IL-37 and STAT3 Link: Extracellular IL-37 has been reported to regulate downstream STAT3 signaling.
    • Study's Novel Finding: Activation of STAT3 effectively reversed the rhIL-37-induced maturation of DCs, conclusively demonstrating that rhIL-37 promotes DCs maturation by inhibiting the phosphorylation of STAT3.

Conclusion

  • Overall Protective Effect: Recombinant human IL-37 (rhIL-37) demonstrably inhibited the development of endometriosis in a mouse model.
  • Key Immune Regulatory Mechanisms:
    1. Modulation of Th1/Th2 Ratio: rhIL-37 increased the ratio of Th1/Th2 cells by inhibiting the production of IL-4 in dendritic cells (DCs).
    2. Induction of DCs Maturation: This was a critical step in the immune rebalancing process.
    3. STAT3 Pathway Inhibition: Mechanistically, rhIL-37 induced DCs maturation through suppressing the phosphorylation of STAT3.
  • Therapeutic Potential: These comprehensive findings suggest a novel therapeutic strategy for endometriosis through the immune-modulating actions of rhIL-37, specifically targeting DCs maturation and Th1/Th2 balance via STAT3 inhibition and IL-4 suppression.