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IL-33/ST2 signalling promotes tumor growth by regulating polarization of alternatively activated macrophages
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Liping Liu, Haoge Luo, Yingdong Xie, Ying Wang, Shiying Ren, Haiyang Sun, Dong Li
Cancer Biology & Medicine | 2025, 22(4) : 376 - 395
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Cancer Biology & Medicine | 2025, 22(4): 376-395
• Original Article •
IL-33/ST2 signalling promotes tumor growth by regulating polarization of alternatively activated macrophages
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Liping Liu, Haoge Luo, Yingdong Xie, Ying Wang, Shiying Ren, Haiyang Sun, Dong Li
Affiliations
  • 1Key Laboratory of Pathobiology, Ministry of Education, Department of Immunology, College of Basic Medical Sciences, Jilin University, Changchun 130021, China
About Author:

Author contributions

Conceived and designed the analysis: Liping Liu, Dong Li.

Collected the data: Liping Liu, Yingdong Xie, Ying Wang.

Contributed data or analysis tools: Liping Liu, Haoge Luo.

Performed the analysis: Liping Liu, Haoge Luo, Shiying Ren, Haiyang Sun.

Wrote the paper: Liping Liu, Dong Li.

Published: 2025-04-15 doi: 10.20892/j.issn.2095-3941.2024.0483
Outline
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Objective:

Suppression of tumorigenicity 2 (ST2), the receptor for interleukin (IL)-33, has a critical role in tumor growth, angiogenesis, metastasis, and immune modulation. The IL-33/ST2 pathway is known to influence the polarization and function of macrophages, which is integral to modulating the tumor microenvironment. However, the precise role of IL-33/ST2 in tumors, particularly non-small cell lung cancer (NSCLC), has not been established.

Methods:

ST2 expression in NSCLC was analysed using a murine model and patient specimens. The effect of the IL-33/ST2 axis on macrophage polarization in NSCLC was determined.

Results:

Elevated ST2 expression was correlated with aggressive tumor growth. Specifically, ST2 expression on macrophages was associated with lung cancer progression and the absence of ST2 on macrophages was associated with diminished tumor growth. IL-33 promoted polarization of alternatively activated macrophages in an ST2-dependent manner that was mediated via the PI3K/Akt signalling pathway. Moreover, IL-33 inhibited T-cell function by inducing the secretion of transforming growth factor β from alternatively activated macrophages.

Conclusions:

Macrophages expressing ST2 can serve as promising therapeutic targets for NSCLC immunotherapy, highlighting the IL-33/ST2 axis as a potential target for future antitumor strategies.

IL-33  /  ST2  /  macrophage polarization  /  non-small cell lung cancer  /  tumor microenvironment
Liping Liu, Haoge Luo, Yingdong Xie, Ying Wang, Shiying Ren, Haiyang Sun, Dong Li. IL-33/ST2 signalling promotes tumor growth by regulating polarization of alternatively activated macrophages[J]. Cancer Biology & Medicine, 2025 , 22 (4) : 376 -395 . DOI: 10.20892/j.issn.2095-3941.2024.0483
Lung cancer accounts for approximately 20% of all cancer-related deaths owing to high morbidity and mortality rates1. Among primary lung cancers, non-small cell lung cancer (NSCLC) constitutes approximately 85% of cases2. Treatments for NSCLC are still limited. Current immunotherapies, such as immune checkpoint inhibitors and CAR-T cells, are far from ideal and have been reported to trigger immune-related adverse events3–5. One critical reason for the limited success of many effective lung cancer therapies is the tumor microenvironment (TME), which directly influences treatment resistance6,7. Therefore, research is required to identify additional strategies to modulate the TME.
Suppression of tumorigenicity 2 (ST2), encoded by the interleukin-1 receptor-like 1 gene (IL1RL1), functions as an interleukin (IL)-33 receptor and was originally considered a stable surface marker of Th2 cells8,9. ST2L and sST2 are two major isoforms of ST2. ST2L binds to IL-33 and triggers type 2 immunity, while sST2 negatively regulates IL-33/ST2 signalling by serving as a decoy receptor and sequestering IL-33 to block its interaction with ST2L10,11. Recent evidence showed that ST2L and sST2 influence the TME and progression of many cancers12–15. However, the role of IL-33/ST2 axis in lung cancer is controversial.
Tumor-associated macrophages (TAMs) exhibit an alternatively activated macrophage (AAM)-like gene expression profile that exerts anti-inflammatory and pro-tumorigenic activities, which constitute the most dominant immune cell population in the TME16–18. Reprogramming tumor-infiltrating macrophages to a classically activated macrophage (CAM)-like phenotype has proven to be beneficial for tumor treatment19,20. CAM-like polarized macrophages promote type-I immune responses against bacterial and viral infections, as well as tumor cells18,21. Our previous studies showed that activation of ST2 via its ligand (IL-33) polarizes macrophages to an AAM-like phenotype, whereas blockage of the IL-33/ST2 pathway leads to CAM-like polarization22,23. However, the exact role of IL-33/ST2 in promoting AAM polarization in NSCLC is unclear.
In the current study the effect of IL-33 in the TME on NSCLC progression was determined. Higher ST2 expression led to more aggressive tumor growth. St2 knockout macrophages had beneficial effects in a murine NSCLC model. IL-33 created an immunosuppressive environment by promoting the polarization of AAMs in an ST2-dependent manner through activation of the PI3K/Akt signalling pathway. Additionally, IL-33 inhibited T-cell function via induction of TGF-β from AAMs. The IL-33/ST2 axis was shown to promote NSCLC and immunosuppression, thereby providing a potential therapeutic target for patients with NSCLC.
Mouse lung carcinoma [Lewis] (Guangzhou Cellcook Biotech Co. Ltd. Guangzhou, China), L929, and 293T cells were cultured in Dulbecco’s Modified Eagle’s Medium [DMEM] (Sartorius CellGenix GmbH, Freiburg, Germany) supplemented with 10% foetal bovine serum [FBS] (Sartorius) and 1% penicillin/streptomycin (Solarbio, Beijing, China). Bone marrow cells were removed from mice (6–8 weeks old) and cultured for 7 days in DMEM supplemented with 10% FBS, 1% penicillin/streptomycin, and 30% conditioned medium from the L929 cells to differentiate into bone marrow-derived macrophages (BMDMs). All cells were cultured in an incubator (Thermo Fisher Scientific, Waltham, MA, USA) at 37°C under 5% CO2. All cell lines were purchased from Guangzhou Cellcook with confirmation of genotypic authentication or acquired from our laboratory.
Il33 transgene (Il33Tg), Il33-deficient (Il33−/−), and Il1rl1-deficient (St2−/−) mice were purchased from Cyagen Biosciences, Inc. (Suzhou, China). All animals were housed under specific pathogen-free (SPF) conditions in temperature-controlled, air-conditioned facilities with unlimited access to food and water. Wide-type (WT) mice were obtained from the same litter. Lewis cells (1 × 106) were injected subcutaneously into the right dorsum of mice to create a mouse tumor model. Tumor volume was estimated using the following formula: tumor volume (mm3) = [length (mm) × short (mm)2]/2. Mouse models of carcinoma in situ were established, as previously described24. Mice were anesthetized using an intraperitoneal injection of Avertin (200 μL [20 mg/mL] 2,2,2-tribromoethanol; Sigma-Aldrich, St. Louis, MO, USA). The lungs were then exposed surgically by making an incision (0.5 cm long) in the left chest and 2 × 105 Lewis cells resuspended in 20 μL of Corning Matrigel (Corning, NY, USA) were injected into the lower left lung using a plastic, 1-mL insulin needle. The surgical wounds were closed with sutures. The mice were randomly assigned to 2 different groups 7 d later and BMDMs (1 × 106 cells/mouse) derived from WT and St2−/− mice were injected into the tail vein with repeated injections on day 10. The mice were sacrificed on day 14. All experiments were performed in accordance with the National Guidelines for Experimental Animal Welfare and were approved by the Animal Welfare and Research Ethics Committee of Jilin University (Approval no. 2022:95) prior to initiation of the study.
Surgically resected lung cancer tissues were obtained from a 61-year-old male with moderately differentiated invasive adenocarcinoma and a 71-year-old male with moderately differentiated invasive adenocarcinoma and immediately submerged in cold phosphate-buffered saline [PBS] (Bioss, Beijing, China) and cut into approximately 5 mm-thick sections. The bulk tissues were placed in an OCT-filled mould (SAKURA, Tokyo, Japan) and snap-frozen on dry ice. Spatial transcriptome sequencing based on the Visium Technology Platform from 10 × Genomics was performed by Shanghai Majorbio Bio-pharm Technology Co., Ltd. (Shanghai, China). Written informed consent was obtained from all participants. This study was approved by the Ethics Committee of the First Hospital of Jilin University (Approval no. 2024:8).
The online Kaplan–Meier plotter tool (https://kmplot.com/analysis/) was used for survival analysis. GEPIA 2 (http://gepia2.cancer-pku.cn/#index) was used for correlation analysis of ST2 expression with CD163 in the lung adenocarcinoma database.
Tumor tissues from mice were formalin-fixed and paraffin-embedded on slides and the paraffin-embedded tissues were de-paraffinised and rehydrated. Antigens were retrieved in a heated citrate buffer (Beyotime, Shanghai, China) for 1 h and incubated with a 3% bovine serum albumin (BSA, Sigma-Aldrich) blocking solution at room temperature for 30 min. The slides were then incubated with anti-CD31 antibody (Cell Signaling Technology, Danvers, MA, USA) overnight at 4°C. The slides were further incubated with the immunohistochemistry (IHC) detection reagent and visualised using a secondary antibody and DAB peroxidase substrate (Fuzhou Maixin Biotech. Co., Ltd, Fuzhou, China).
Tumor tissue sections were incubated with primary antibodies (anti-ST2; R&D Systems, Minneapolis, MN, USA) and (anti-CD206; Cell Signaling Technology) at 4°C overnight, followed by incubation with the corresponding antibodies for 1 h at room temperature. Nuclei were stained with 4′,6-diamidino-2-phenylindole [DAPI] (Beyotime) for 5 min. The slides were mounted on coverslips and imaged under a microscope (Olympus, Tokyo, Japan).
BMDMs from WT and St2−/− mice were cultured in 96-well plates for 48 h to study cellular proliferation. Lewis cells were co-cultured with BMDM-Ctrl, BMDM-flIl33, or BMDM-cIl33 cells for 48 h. The Cell Counting Kit-8 [CCK-8] (Bioss) was used to detect cell proliferation based on absorbance values following the manufacturer’s protocol.
Cellular invasion was measured using Transwell inserts containing 8-μm membrane filters (LABSELECT, Jinan, China). Lewis cells (2 × 104) were seeded in serum-free medium in the upper chamber of a Transwell insert coated with Matrigel (Corning). BMDM-Ctrl, BMDM-flIl33, and BMDM-cIl33 cells (1 × 105) in fresh medium containing 10% FBS were seeded in the lower Transwell chamber. After incubation for 24 h, cells on the upper surface were washed with PBS, fixed with 4% paraformaldehyde for 15 min, and stained with 0.1% crystal violet for 15 min. Invasive cells were counted under a microscope.
Lentiviral production and transduction were performed using a lentiviral vector containing a lentiviral packaging mix. The following mouse lentivirus packaging plasmids were purchased from HanBio Biotechnology Co., Ltd. (Shanghai, China): control, full-length Il33 (flIl33, 1–266 amino acids); Il33 C-terminal domain (cIl33, 109–266 amino acids); pMD2G plasmids; and psPAX2 plasmids First, the plasmids were extracted (TransGen Biotech, Beijing, China) and transfected into 293T cells using a transfection reagent (Yeasen, Shanghai, China) for 48 h. The supernatant was collected and centrifuged in ultrafiltration tubes (Merck, Darmstadt, Germany) to obtain the lentivirus. The lentivirus was transfected into Lewis cells using polybrene (Yeasen) and puromycin (Sigma-Aldrich) was added 72 h after transfection to screen the cells. After 1 week of screening, stable monoclonal cells were obtained, including Lewis-Ctrl, Lewis-flIl33, and Lewis-cIl33. To obtain BMDMs expressing flIl33 and cIl33, the lentivirus was transfected into BMDMs, BMDM-Ctrl, BMDM-flIl33, and BMDM-cIl33 cells were obtained after transfection for 72 h.
Fresh tumor tissues were cut into small pieces. The tissues were dissociated using a grinder and centrifuged at 400×g for 5 min. The erythrocytes were lysed (Solarbio) and the cell suspension was incubated with antibodies. The cultured cells were then processed. Briefly, 100 μL of the cell suspension was incubated for 10 min with FcR blocking reagent (Miltenyi Biotec, Bergisch Gladbach, Germany). The cells were washed with PBS to remove the unbound FcR blocking reagent. For surface staining, APC anti-mouse CD45 antibody (BioLegend, San Diego, CA, USA), PerCP anti-mouse F4/80 antibody (BD Biosciences, San Jose, CA, USA.), PE anti-mouse CD206 antibody (BD Biosciences), FITC anti-mouse CD11c antibody (BD Biosciences), PE anti-mouse NK1.1 antibody (BD Biosciences), PE anti-mouse B220 antibody (BD Biosciences), PE anti-mouse CD3 antibody (eBioscience, USA), FITC anti-mouse CD4 antibody (eBioscience, San Diego, CA, USA), PerCP-Cy5.5 anti-mouse CD8 antibody (eBioscience), APC anti-mouse CD279 (PD-1) antibody (BioLegend), and PerCP anti-mouse CTLA4 antibody (BioLegend) were added as appropriate, incubated at 4°C for 30 min, and washed with the FACS buffer (1% FBS in PBS). To stain intracellular molecules, cells were fixed with 4% paraformaldehyde for 50 min, washed twice with 0.1% saponin-PBS for permeabilisation, stained with the PE anti-mouse IFNγ antibody (eBioscience), PE anti-mouse perforin antibody (eBioscience), PE anti-mouse Foxp3 antibody (Biolegend) as appropriate for 45 min, washed with FACS buffer. All samples were analysed using a flow cytometer (Guava Technologies, Hayward, CA, USA) and analysed using FlowJo v10 (FlowJo, LLC, Ashland, OR, USA).
BMDMs from WT and St2−/− mice were cultured in 6-well plates. Lewis cell debris with GFP fluorescence was added to the culture supernatant and incubated for 24 h. The BMDMs were collected, labelled with F480 antibody, and the percentage of F480-positive cells containing GFP was detected using flow cytometry.
The cytokine concentration in the culture media from co-culture experiments and tumor tissues was quantitatively determined using an ELISA following the manufacturer’s instructions, including TGF-β (Solarbio) and IL-33 (R&D Systems). The absorbance of each well was measured at 450 nm using a microplate reader (EPOCH2, BioTek, Winooski, VT, USA).
Total RNA was extracted using TRIzol reagent (Takara, Kusatsu, Japan) and reverse-transcribed into cDNA using a cDNA Synthesis Kit (TOLO Biotechnology, Shanghai, China). Real-time PCR was performed using an Agilent Mx3000P machine (Agilent, Santa Clara, CA, USA) with SYBR Green Master Mix (Takara). The following forward and reverse primer sequences for the test genes were used: Gapdh (forward, 5′-GCACCGTCAAGGCTGAGAAC-3′; reverse, 5′-GGATCTCGCTCCTGGAAGATG-3′); Mrc1 (forward, 5′-CTCTGTTCAGCTATTGGACGCCG-3′); reverse, 5′-TGGCACTCCCAAACATAATTTGA-3′); Tgfb (forward, 5′-AGGCGGTGCTCGCTTTGTA-3′; reverse, 5′-CTGCTTCCCGAATGTCTGA-3′); and Arg1 (forward, 5′-CTCCAAGCCAAAGTCCTTAGAG-3′; reverse, 5′-AGGAGCTGTCATTAGGGACA-3′). The target mRNA expression was calculated relative to the amount of GAPDH using the 2−ΔΔCt method.
The total cellular protein was collected and lysed using RIPA (Beyotime) and protease inhibitors (Roche, Basel, Switzerland) at 4°C for 30 min, centrifuged at 10,000 × g for 30 min, and the supernatant was collected. The protein concentration was determined using a BCA Protein Quantification Kit (Biomed, Beijing, China). All samples were separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and transferred onto polyvinylidene fluoride (PVDF) membranes (Merck). The membrane was blocked with 5% skim milk at room temperature for 2 h followed by incubation overnight at 4°C with the primary antibody against CD206 (Cell Signaling Technology), PI3K (ZenBio Science, Chengdu, China), P-PI3K (Affinity Biosciences, Changzhou, China), Akt (ZenBio Science), P-Akt (ZenBio Science), and GAPDH (Wuhan Sanying, Wuhan, China). The PVDF membranes were washed three times with Tris-buffered saline with Tween-20 [TBST] (Solarbio) for 5 min each, incubated with an HRP-conjugated secondary antibody (Bioss) for 40 min at room temperature, then washed three times with TBST. Specific bands were detected using an enhanced chemiluminescence detection reagent (Sparkjade, Jinan, China).
RNA-Seq was performed by Sangon Biotechnology (Shanghai, China). Briefly, BMDMs from WT, Il33Tg, and St2−/− mice were stimulated with IL-4 for 48 h and total RNA was extracted using the TRIzol Reagent (Takara). RNA integrity was assessed using an Agilent Bioanalyzer 2100. Only samples with clean rRNA profiles were used in the subsequent steps. Paired-end sequencing was performed using an Illumina HighSeq 4000 instrument (Illumina, San Diego, CA, USA).
Macrophages and Lewis cells were co-cultured using Transwell inserts containing 0.4-μm membrane filters (LABSELECT). BMDMs from WT or St2−/− mice were placed in the lower Transwell chamber with Lewis-NC (Lewis cells). Lewis-Ctrl, Lewis-flIl33, and Lewis-cIl33 cells were added to the upper Transwell chamber and incubated for 48 h. The PI3K/Akt signalling pathway was inhibited using a PI3K-IN-1 inhibitor (catalog no. HY-12068; MCE, Monmouth Junction, NJ, USA) in the co-culture system.
T cells were sorted using the EasySep™ Mouse CD8+ T Cell Isolation Kit and the EasySep™ Mouse CD4+ T Cell Isolation Kit (STEMCELL, Vancouver, Canada) following the manufacturer’s instructions. Briefly, splenocytes were resuspended in Dulbecco’s phosphate-buffered saline [DPBS] (Servicebio, Wuhan, China). One millilitre of the cell suspension was placed in a sorting tube. An FcR blocker and isolation cocktail were then added to the sample and incubated for 10 min. RapidSpheres™ were added to the samples and incubated for 5 min. Subsequently, 1.3 mL of DPBS was added to give a final volume of 2.5 mL. The sorting tube was placed in a magnet apparatus for 5 min at room temperature and the supernatants containing the cells were collected and used for further experiments.
The BMDM supernatants co-cultured with Lewis-NC, Lewis-Ctrl, Lewis-flIl33, and Lewis-cIl33 were collected and used to resuspend sorted CD4+ T cells and CD8+ T cells, which were subsequently incubated in 96-well plates for 72 h. TGF-β was neutralised using TGF-β neutralising antibody (Biolegend). The cells were collected for subsequent experiments.
All experimental results were obtained from at least three replicates. The sample size for both the animal model and in vitro experiments was decided based on expected variance and standard deviations from pilot studies. The significance was set at 0.05 with a power of 0.9 following the guidelines published in ILAR Journal25. The statistical significance of differences was tested using one-way analysis of variance (ANOVA) or unpaired two-tailed t-tests. The results are presented as the mean ± standard deviation (SD). Analyses were performed using GraphPad Prism software (version 8.0; GraphPad Software, Boston, MA, USA). Statistical significance was set at a P < 0.05.
Immunofluorescence analysis was performed on mouse lung cancer samples to determine the clinical relevance of ST2 in the context of lung adenocarcinoma (LUAD). Th ST2 expression was significantly higher in tumor tissues compared to adjacent normal lung tissues (Figure 1A). A Kaplan–Meier plot generated from an online dataset comprised of 10 independent cohorts (a total of 1161 patients) revealed that high ST2 expression correlates with reduced survival rates in patients with LUAD (Figure S1)26. The detailed characteristics of each dataset are presented in Table S1. WT, Il33Tg, Il33−/−, and St2−/− mice were inoculated with Lewis lung carcinoma cells to further investigate the role of IL-33/ST2 in lung cancer. The growth of tumors was faster in Il33Tg mice (Figure 1B), while Il33 and St2 knockout inhibited tumor growth (Figure 1C). These results suggested that the IL-33/ST2 axis promotes lung cancer progression.
ST2 expression was determined in various cell types by analysing single-cell sequencing data from 49 patients with lung cancer to identify the cells in the TME with high ST2 expression27. ST2 was expressed in macrophages, fibroblasts, and T cells (Figure 1D). Macrophage polarization has an important role in the TME. A correlation analysis was performed using data from the GEPIA2 website to determine the relevance of ST2 and AAMs in lung adenocarcinoma28. Expression of ST2 and CD163, which are primarily expressed in AAMs29, was shown to be positively correlated with LAUD (Figure 1E). Moreover, spatial transcriptomic data from biopsy tissues of patients with LUAD showed overlapping expression of ST2 and CD163 in tumor tissues (Figure 1F). These data highlighted the potential functional role of ST2+ macrophages in lung cancer.
St2 was knocked out and the effect on macrophage function was determined in vitro. St2 knockout did not affect the proliferative and phagocytic function of macrophages (Figure 2A, B). A mouse model of carcinoma in situ was constructed by inoculating the lungs of mice with Lewis cells to further determine whether St2 knockout macrophages (St2−/− BMDMs) inhibit tumor growth in vivo. WT and St2−/− BMDMs were administered via tail vein injection into mice with carcinoma in situ. The St2−/− BMDM-treated group inhibited tumor growth (Figure 2C). Expression of CD31 in tumor tissues was assessed to determine the effect of St2−/− BMDMs on angiogenesis. IHC results showed that St2−/− BMDMs inhibited CD31 expression (Figure 2D). Immunofluorescence staining of ST2 and the marker of AAMs (CD206) in mouse tumor tissues showed that the St2−/− BMDM-treated group exhibited fewer ST2+ AAMs than the WT BMDMs group (Figure 2E). Thus, transfer of St2−/− BMDMs inhibited tumor growth by decreasing polarization of AAMs in the TME.
A lentivirus containing flIl33 and cIl33 without the nuclear localisation domain was constructed to determine the local effects of the IL-33/ST2 axis on tumor growth and eliminate the potential ST2-independent functions of flIL-3330. Lewis cells overexpressing flIl33 (Lewis-flIl33), cIl33 (Lewis-cIl33), and a control (Lewis-Ctrl) were successfully generated. Lewis-Ctrl, Lewis-flIl33 and Lewis-cIl33 were implanted intradermally into WT mice to assay the effects of IL-33/ST2 in vivo. Tumor growth was significantly promoted in the Lewis-flIl33 and Lewis-cIl33 groups compared to the Lewis-Ctrl group (Figure 3A). Moreover, the ELISA results showed that IL-33 levels increased in the tumor tissues of the Lewis-flIl33 and Lewis-cIl33 groups (Figure 3B). The expression profiles of various immune cell populations were assessed using flow cytometry to determine the effect of local IL-33 on the TME. The proportion of leucocytes, macrophages, AAMs, and CD4+ T cells increased in the Lewis-flIl33 and Lewis-cIl33 groups, while the proportion of natural killer (NK) cells decreased compared to the Lewis-Ctrl group; the decreased proportion of CD8+ T cells only occurred in Lewis-cIl33 groups (Figure 3C-G, Figure S2A-E). No significant changes in other immune cells, such as dendritic cells (DC) cells, T cells, and B cells, were detected (Figure 3H-J, Figure S2F-H). Immunohistochemistry (IHC) and H&E staining were used to detect pathologic changes in the tumor tissues to further determine the effect of IL-33 on the TME. Severe necrosis and immune cell infiltration were noted in the Lewis-flIl33 and Lewis-cIl33 groups compared to the control group (Figure 3K). IHC analysis showed increased expression of CD31 in the Lewis-flIl33 and Lewis-cIl33 groups (Figure 3L). Taken together, these results suggested that IL-33/ST2 exerts a pro-tumor effect by creating an immunosuppressive microenvironment.
IL-33 is known to promote tumor growth by increasing AAM-type macrophage infiltration via the ST2 axis in B16 melanoma23. Lewis (Lewis-NC), Lewis-Ctrl, Lewis-flIl33, and Lewis-cIl33 cells were co-cultured with WT BMDMs in vitro to determine if IL-33 influences lung cancer development by affecting macrophage polarization in the TME. The flow cytometry results showed that AAMs increased in the Lewis-flIl33 and Lewis-cIl33 groups (Figure 4A, Figure S3A). The levels of CD206 protein and Mrc1, Arg1, and Tgfb gene expression were upregulated in WT BMDMs in the Lewis-flIl33 and Lewis-cIl33 groups (Figure 4B, C). Conditioned media were collected from Lewis-NC, Lewis-Ctrl, Lewis-flIl33, and Lewis-cIl33 cells, which were co-cultured with WT BMDMs, compared to media from cells that were not co-cultured to determine the secretion of IL-33. Lewis-flIl33 and Lewis-cIl33 cells secreted IL-33 with greater secretion by Lewis-cIl33 cells than Lewis-flIl33 cells. Moreover, Lewis-flIl33 and Lewis-cIl33 cells promoted secretion of IL-33 from macrophages (Figure 4D). St2−/− BMDMs were co-cultured with Lewis-Ctrl, Lewis-flIl33, and Lewis-cIl33 cells to further investigate whether macrophage polarization in the co-culture system was dependent on tumor cell-derived IL-33. Flow cytometry showed that AAMs did not increase in the Lewis-flIl33 and Lewis-cIl33 groups (Figure 4E, Figure S3B). Moreover, the levels of CD206 protein and Mrc1, Arg1, and Tgfb gene expression were not significantly altered (Figure 4F, G) and IL-33 expression did not increase in the supernatant of the co-culture system (Figure 4H). Thus, IL-33 secreted by tumor cells promoted IL-33 secretion by macrophages and promoted polarization of AAMs, which was ST2-dependent.
Differentially enriched pathways in WT BMDMs, Il33Tg BMDMs, and St2−/− BMDMs stimulated with IL-4 were screened using transcriptome sequencing to identify the relevant IL-33/ST2 pathways in macrophage polarization. A total of 4756 differentially expressed genes were noted at the transcript level in St2−/− BMDMs compared to WT BMDMs, 2220 differentially expressed genes were noted at the transcript level in Il33Tg BMDMs compared to WT BMDMs, and 4215 differentially expressed genes were noted at the transcript level in St2−/− BMDMs compared to Il33Tg BMDMs (Figure 5A). The signalling pathways enriched for differentially expressed genes according to the KEGG database showed that the groups were enriched for the PI3K/Akt signalling pathway (Figure 5B). In addition, PI3K/Akt signalling was shown to be highly activated in macrophages compared to other immune cells in lung cancer tissues by analysing single-cell sequencing data from 49 patients with lung cancer (Figure 5C)27. The levels of PI3K, p-PI3K, Akt, and p-Akt expression in WT BMDMs were measured in the co-culture system using western blot to determine whether the IL-33/ST2 axis promotes polarization of AAMs by activating the PI3K/Akt signalling pathway. Lewis-flIl33 and Lewis-cIl33 cells co-cultured with WT BMDMs showed enhanced activation of the PI3K/Akt pathway (Figure 5D, G). In contrast, no significant changes were noted in the co-culture system with St2−/− BMDMs (Figure 5E, H). A PI3K/Akt inhibitor was added to the co-culture system to further explore whether macrophage polarization was promoted through activation of the PI3K/Akt pathway. The levels of CD206 protein were inhibited in BMDMs co-cultured with Lewis-flIl33 and Lewis-cIl33 cells after the addition of a PI3K/Akt inhibitor (Figure 5F, I). Flow cytometry results showed that AAMs were decreased in BMDMs co-cultured with Lewis-flIl33 and Lewis-cIl33 cells after the addition of a PI3K/Akt inhibitor (Figure 5J, Figure S4). Mrc1, Arg1, and Tgfb gene expression was inhibited in BMDMs co-cultured with Lewis-flIl33 and Lewis-cIl33 cells after addition of a PI3K/Akt inhibitor (Figure 5K). Overall, these results indicated that the IL-33/ST2 axis activates the PI3K/Akt signalling pathway during AAM polarization.
Single-cell sequencing of samples was performed from 49 patients with lung cancer to determine IL-33 expression in the TME27. Macrophages and fibroblasts were the cells expressing IL-33 in the human TME (Figure 6A). Lentiviruses were used to transfer flIl33 and cIl33 into the BMDMs and co-cultured them with Lewis cells to determine the effect of macrophages expressing Il33 on lung cancer in vivo. Macrophages overexpressing IL-33 promoted the proliferation and invasive ability of Lewis cells (Figure 6B, C). Macrophages overexpressing flIl33 and cIl33 were stimulated with IL-4 in vitro to further determine whether Il33-expressing macrophages influence macrophage polarization in the TME. The results of flow cytometry suggested that IL-33 promotes IL-4-induced AAM polarization (Figure 6D, Figure S5). Mrc1, Arg1, and Tgfb gene expression was upregulated in the BMDM-flIl33 and BMDM-cIl33 groups compared to the BMDM-Ctrl group (Figure 6E). These results indicated that IL-33/ST2 axis-polarized macrophages promote cancer progression.
CD4+ and CD8+ T cells were sorted from mouse spleens and cultured in the supernatant derived from BMDMs co-cultured with Lewis-NC, Lewis-Ctrl, Lewis-flIl33, and Lewis-cIl33 cells to further define the role of AAMs in the TME. The ability of CD8+ T cells to secrete IFN-γ and perforin was significantly inhibited by the supernatants from BMDMs co-cultured with Lewis-flIl33 and Lewis-cIl33 cells. Furthermore, PD-1 and CTLA4 expression on CD8+ T cells increased when cultured with BMDM supernatants co-cultured with Lewis-flIl33 and Lewis-cIl33 cells (Figure 7A, Figure S6A). Treg differentiation was also promoted in CD4+ T cells cultured with the BMDM supernatants co-cultured with Lewis-flIl33 and Lewis-cIl33 cells (Figure 7B, Figure S6B). The ability of CD4+ T cells to secrete IFN-γ was significantly inhibited when cultured with BMDM supernatants co-cultured with Leiws-flIl33 and Lewis-cIl33 cells (Figure 7C, Figure S6C). ELISA showed that BMDMs co-cultured with Lewis-flIl33 and Lewis-cIl33 groups secreted higher TGF-β compared to the Lewis-Ctrl group (Figure 7D). TGF-β neutralising antibody was added in the supernatant derived from BMDMs that had been co-cultured with Lewis-cIl33 cells to confirm that TGF-β influences T cell function. Neutralisation of TGF-β promoted the expression of CD8+ T cell IFN-γ and perforin (Figure 7E, Figure S6D), inhibited Treg cell differentiation, and promoted CD4+ T cell IFN-γ expression (Figure 7F, Figure S6E). Taken together, the results demonstrated that the IL-33/ST2 axis promoted secretion of TGF-β from AAMs, which inhibited T cell function.
IL-33 exhibits ST2-dependent pro-tumor effects in lung cancer. IL-33 promotes polarization of alternatively activated macrophages by activating the PI3K/Akt signalling pathway31. Additionally, IL-33 exhibits an immunosuppressive role by inhibiting T-cell function via induction of TGF-β from AAMs32–34 (Figure 8). Furthermore, ST2-deficient macrophages impede tumor growth. Overall, these findings suggest that ST2-expressing macrophages are potential targets for NSCLC immunotherapy.
Patients with NSCLC have enhanced ST2 expression in cancer tissues compared to adjacent healthy tissues and the level of expression correlates with the clinical stage35. A previous observational study showed decreased levels of ST2 in lung cancer tissues compared to healthy tissues, which were inversely correlated with cancer stage and survival rates36. Our results also showed that higher ST2 expression leads to more aggressive tumor growth. Furthermore, a higher ST2 concentration existed in tumor tissues than adjacent normal tissues in mice. We subsequently extended this finding to the mechanism underlying the role of the IL-33-ST2 axis.
Tumor growth was accelerated in Il33 transgenic mice, whereas knockout of Il33 and St2 inhibited tumor growth. IL-33 is comprised of two distinct functional domains (a nuclear domain that has immunosuppressive functions and an IL-1-like cytokine domain that binds to its receptor ST2)37–40. In the current study tumor growth was shown to be significantly promoted in Lewis-flIl33 and Lewis-cIl33 mice compared to Lewis-Ctrl mice, highlighting the role of IL-33/ST2 in lung cancer. Collectively, the results suggest that IL-33/ST2 promotes lung cancer progression. Therefore, targeting the IL-33/ST2 axis is a promising immunotherapy for the treatment of NSCLC.
Our results showed that IL-33/ST2 can create an immunosuppressive microenvironment by promoting polarization of AAMs, with AAMs serving as recipients and source of IL-33 in the TME, further promoting lung cancer. Notably, Lewis-flIl33 polarizes macrophages toward AAMs, although the secreted IL-33 level was significantly lower in Lewis-flIl33 than Lewis-cIl33, suggesting that low levels of IL-33 may have a pro-tumorigenic role. Owing to pleiotropic functions, IL-33/ST2 modulates recruitment of immune cells and the TME, which exhibit pro- or anti-tumorigenic effects depending on surrounding cellular and soluble factors in the TME41–43. Additionally, the IL-33/ST2 axis has been documented to enhance the differentiation and maturation of DC cells, consequently bolstering the anti-tumor efficacy of CD8+ T and NK cells, while concurrently suppressing the proliferation of lung cancer cells44. This discrepancy can be attributed to the heterogeneity and complexity of TME components45.
PI3K/Akt signalling mediated by mTORC1 regulates the effector responses of macrophages, which in turn affect innate immune responses46 and macrophage polarization47. In addition, the IL-33/ST2 axis activates the PI3K/AKT/NF-κB signalling pathway through TRAF6, thereby promoting VEGFA-mediated tumor angiogenesis31. In the current study IL-33 was shown to induce polarization of AAMs by activating the PI3K/Akt pathway, which is consistent with the findings of a previous study48.
Direct activation of ST2 via stimulation with IL-33 decreases PD-1 expression in CTLs49. However, IL-33-polarized AAMs were shown to promote PD1 and CTLA4 expression in CD8+ T cells. Increased infiltration of CD4+ within Lewis-flIl33 and Lewis-cIl33 tumors was noted compared to Lewis-Ctrl tumors, but decreased infiltration of CD8+ T cells was only occurred in Lewis-cIl33 compared to Lewis-Ctrl tumors. In addition, a notably high proportion of CD3+CD4–CD8– cells was detected in these tumors, which is consistent with previous findings50. We hypothesise that these cells contribute to the tumor immunosuppressive microenvironment. Moreover, the secretion of TGF-β by IL-33/ST2-polarized AAMs promoted the differentiation of Treg cells and inhibited the secretion of IFN-γ and perforin by CD8+ T cells.
Several major treatment options are available for NSCLC. Lobectomy is currently considered the best treatment for early-stage NSCLC51,52. Neoadjuvant chemotherapy is feasible and immunotherapy may be the best therapeutic strategy for neoadjuvant treatment of early-stage NSCLC53. The most common immune checkpoint inhibitors, such as PD1, PDL1, and CTLA-4 blockade and CAR-T, have been used to treat NSCLC54–56. While anti-monoclonal antibodies have been used in clinical applications, the efficacy in cases of poor prognosis may be compromised by factors, such as dysregulation of cytokine expression, including IL-33. Our results highlight the potential of ST2 as a therapeutic target for NSCLC immunotherapy.
The findings herein support targeting of the pro-tumor cytokine, IL-33, and its receptor (ST2) as an effective strategy to convert the immunoevasive TME into an immunoreactive TME for tumor therapy.
  • This study was supported by the National Key R&D Program of China (2023YFC2413100), the National Natural Science Foundation of China (No. 81501423), and the Fundamental Research Funds for the Central Universities.
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Year 2025 volume 22 Issue 4
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doi: 10.20892/j.issn.2095-3941.2024.0483
  • Receive Date:2024-10-26
  • Online Date:2026-11-06
  • Published:2025-04-15
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  • Received:2024-10-26
  • Accepted:2025-02-20
Funding
This study was supported by the National Key R&D Program of China (2023YFC2413100), the National Natural Science Foundation of China (No. 81501423), and the Fundamental Research Funds for the Central Universities.
Affiliations
    1Key Laboratory of Pathobiology, Ministry of Education, Department of Immunology, College of Basic Medical Sciences, Jilin University, Changchun 130021, China

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Correspondence to: Dong Li, E-mail:
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表12种不同金属材料的力学参数
科
Family
属数
Number of
genus
种数
Number of
species
占总种数比例
Percentage of
total species (%)
属
Genus
种数
Number of
species
占总种数比例
Percentage of total
species (%)
鹅膏菌科Amanitaceae 2 11 5.26 鹅膏菌属 Amanita 10 4.78
小菇科 Mycenaceae 2 12 5.74 丝盖伞属 Inocybe 5 2.39
多孔菌科 Polyporaceae 8 14 6.70 蜡蘑属 Laccaria 5 2.39
红菇科 Russulaceae 3 23 11.00 小皮伞属 Marasmius 6 2.87
小菇属 Mycena 11 5.26
光柄菇属 Pluteus 5 2.39
红菇属 Russula 17 8.13
栓菌属 Trametes 5 2.39
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