English

• Metal-based antibacterial materials containing metals typically incorporate metallic elements such as silver, copper, zinc, and cobalt, which exhibit natural antibacterial properties [1]. The antibacterial mechanism of metal-based antimicrobial materials was related to the release of metal ions and ligand properties. The released metal ions change the surrounding environment of bacteria, break the ion balance, and destroy the ion channel and membrane integrity. With the rupture of the membrane and the outflow of the cytoplasm, the bacteria finally died [2]. Furthermore, the physicochemical properties of metal-based antimicrobial materials are highly tunable and optimizable to address diverse application demands. Consequently, compared to conventional antibiotics, these materials exhibit reduced propensity for inducing drug resistance while offering tunable antimicrobial performance and cost-effectiveness. This combination of attributes renders them more versatile than antibiotics, promising deployment across broad-spectrum antimicrobial strategies [3]. While many metal-based antimicrobial materials exert antibacterial effects through the controlled release of bioactive metal ions into the microenvironment, excessive ion accumulation poses dose-dependent toxicity risks. For example, Cu induces membrane potential disruption, membrane damage, reactive oxygen species (ROS) generation, and electron transport chain impairment, while Ag causes poor metabolizability, potential neurotoxicity, and vascular effects [4, 5]. Iron, an essential trace element, represents the most abundant micronutrient in the human body. Iron plays various roles in the human body, including promoting hemoglobin synthesis, regulating immune function, maintaining energy metabolism, supporting brain development and cognitive function, and participating in redox reactions. Based on this, we synthesized an iron-based nanosized molecular iron-oxo clusters (MIC) with high biosafety, excellent water solubility, and stability in aqueous solutions. We administered MIC to sepsis models to evaluate its antimicrobial therapeutic efficacy, given that sepsis is an infection-driven critical illness.

  Sepsis is a leading cause of mortality worldwide, driven by dysfunctional immune responses to microbial invasion [6]. Current treatment primarily involves broad-spectrum antibiotics [7], which often result in suboptimal patient outcomes, including poor prognoses and the exacerbation of antimicrobial resistance [8]. The overuse of these antibiotics has contributed to the emergence of multidrug-resistant pathogens, complicating treatment and making infections harder to control. Moreover, these approaches fail to address the underlying immune dysregulation characteristic of sepsis, leading to prolonged inflammatory responses, immune paralysis, and multi-organ failure [9, 10]. As such, there is a pressing need for novel therapeutic interventions that not only target infections but also modulate the host immune response, with the aim of reducing excessive inflammation, restoring functional immunity, and improving recovery outcomes in this life-threatening condition.

  We found that MIC does not inhibit bacterial growth directly, while revealing its ability to enhance IgG and IgA levels to increase humoral immune reactivity. We found that administration of MIC reduced bacterial burden in the blood and peritoneal fluid, increased survival rate, improved body temperature, and decreased inflammatory cytokine levels in septic mice. Further research revealed that MIC could enhance B cell metabolic activity and reduce B cell apoptosis.

  A novel and safe water-soluble nanosized MIC was obtained by the hydrothermal reaction followed by evaporation incubation at 25 ℃. The molecular formula of MIC is C₉₆H₁₀₈Fe₂₈O₁₄₄. Elemental analysis, theoretical value (%): Fe 30.51, C 22.46; actual value (%): Fe 30.52, C 22.45. Fig. 1a demonstrates the structural unit {Fe14} in the MIC molecule, which is assembled into the MIC molecule via a tartrate ligand. The X-ray diffraction (XRD) and FT-IR of the MIC are shown in Figs. S3a and b (Supporting information), showing the purity of the synthesized cluster. FT-IR (cm^-1) of MIC: 553(m), 670(w), 715(m), 811(w), 982(w), 1040(w), 1400(s), 1560(m), 1660(w), 3420 (m). Figs. 1b and c show the size of the nano-cluster with a maximum width of 27.1 Å and a height of 9.0 Å. Dynamic light scattering (DLS), performed using a Zetasizer instrumentation system, characterizes the Brownian motion of particles. The zeta potential (Fig. 1d), indicates a weak negative charge on the MIC surface, suggesting good compatibility with water. Small angle X-ray scattering (SAXS) analysis demonstrated that MIC is uniformly distributed in aqueous solution without agglomeration. The SAXS profile indicated that MIC retains its structural integrity even after 12 h (Fig. 1e, red line vs. black line), confirming the cluster's stability in aqueous solution. Crystallographic data (CCDC: 2348645) showed that the cluster crystallized in the space group P2₁2₁2 (Table S1 in Supporting information). Its crystal data, partial bond lengths, partial bond angles, and valence bond calculations are displayed in Tables S1-S4 (Supporting information). Meanwhile, the X-ray photoelectron spectroscopy (XPS) test of Fe 2p on the sample MIC was performed (Fig. S3c in Supporting information). The Fe 2p XPS pattern was divided into four peaks, the peaks at 710.9 and 724.9 eV were attributed to Fe³⁺ 2p_3/2 and Fe³⁺ 2p_1/2, respectively, and the peaks at 714.4 and 729.8 eV were attributed to Fe³⁺ satellite peaks [11–13].

  Figure 1

  

  Figure 1.  (a) Polyhedral and ball-stick configurations of sample MIC. Fe: blue; O: red; C: dark grey. (b, c) MIC space-filling representations. (d) Zeta potential of MIC (n = 3). (e) SAXS spectra of MIC aqueous solution (the red line represents the SAXS of MIC after 12 h of dissolution in aqueous solution, and the black line represents the initial state) (n = 3).

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  We tested the cytotoxicity of MIC and several common iron compounds against two major human lymphocyte lines (human B lymphoma cells and monocytic leukemia cells). The results showed that Fe(NO₃)₃ and FeCl₃ exhibit high aqueous solubility, but they elicit significant cytotoxicity manifested by reduced cell viability and distinct morphological alterations. Fe₂O₃ and Fe₃O₄ exhibit low aqueous solubility, forming insoluble particulate aggregates observable under phase-contrast microscopy, both of which significantly reduce cell viability. These findings collectively confirm the cytotoxicity of these four common iron-based compounds. While MIC caused minimal changes in cell morphology and maintained cell counts comparable to the control (Ctrl) (PBS) group, suggesting low cytotoxicity of MIC (Figs. S4a-d in Supporting information).

  To investigate the effect of MIC for bacterial clearance, a minimum inhibitory concentration experiment was performed. MIC was added directly to bacterial suspensions in vitro, but no significant changes in bacterial counts were observed, indicating that MIC lacks direct bactericidal activity (Figs. S5a and b in Supporting information).

  Next, the bactericidal effect of MIC in vivo was evaluated using serum from MIC-treated rats in lysis experiments (all in vivo experiments were performed following the National Guidelines for Experimental Animal Welfare and were approved by Animal Welfare and Research Ethics Committee of Jilin University, Approval No. 2024:286). The optical density at 600 nm (OD₆₀₀) of the bacterial solution mixed with serum from the Ctrl group was significantly higher than that of serum from the MIC-treated group (Figs. 2a and b). Similarly, bacterial counts in serum from the Ctrl group mixed with a 1 × 10⁶-fold diluted bacterial solution were significantly higher than those in the MIC-treated group (Figs. 2a and c). Even when the serum was diluted 10-fold and mixed with a 1 × 10⁶-fold diluted bacterial solution, the bacterial counts in the MIC-treated group remained significantly lower than the Ctrl group (Figs. 2a and d).

  Figure 2

  

  Figure 2.  MIC boosts humoral immunity to eliminate bacteria. (a) Representative images of bacterial culture of bacterial solution mixed with Sprague-Dawley rats' serum after different treatments. (b) Measure the OD₆₀₀ of a mixed solution with a colony count greater than 300. OD₆₀₀ of bacterial solution (dilution 1:100) equal volume mixed with serum. (c) Bacteria counts of LB agar medium after bacterial solution (dilution 1:10⁶) equal volume mixed with serum. (d) Bacteria counts of LB agar medium after bacterial solution (dilution 1:10⁶) equal volume mixed with serum (dilution 1:10). The levels of (e) IgM, (f) IgG, and (g) IgA in the serum of Sprague-Dawley rats after different administrations. n = 3. Data are presented as mean ± SD, ^*P < 0.05, ^**P < 0.01, ^***P < 0.001.

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  Furthermore, we measured the concentrations of immunoglobulins in the serum and found that MIC administration significantly increased the levels of immunoglobulin G (IgG) and immunoglobulin A (IgA), particularly in the 1 mg/kg treatment group (Figs. 2e-g). These findings suggest that MIC reduces bacterial burden by enhancing the concentration of natural antibodies in the bloodstream, as these rats were not subjected to surgery, further indicating an immune-mediated mechanism of bacterial clearance.

  The mouse lethal dose of 50% (LD₅₀) of MIC was determined to be 150 mg/kg (95% CI: 150–200 mg/kg, Table S6 in Supporting information). The LD₅₀ value, being 75 times higher than the appropriate therapeutic dose (1 mg/kg per injection; 2 injections given), highlights the favorable safety profile of MIC.

  We evaluated the therapeutic effects of MIC alongside three other newly synthesized cluster compounds (Cluster-1, Cluster-3 [12], and MIC—NaK [14]) in a cecal ligation and puncture (CLP) induced sepsis model. The results demonstrated that mice in the MIC group exhibited a higher survival rate (Fig. S6a in Supporting information). Based on the dose-response profiling of MIC, an optimized dose of 1 mg/kg demonstrating superior therapeutic efficacy was selected for subsequent in vivo investigations (Fig. S6b in Supporting information). MIC treatment improved survival rates and stabilized body temperature in CLP mice (Figs. 3a and b). It also reduced pro-inflammatory cytokines, including IL-6, while increasing immunoregulatory cytokines, such as IL-4 and IL-10 in the bloodstream and bronchoalveolar lavage fluid (BALF) (Fig. 3c and Fig. S6c in Supporting information). MIC administration significantly decreased lung damage scores (Figs. 4a and b), and ameliorated liver injury, as indicated by reductions in serum aspartate aminotransferase (AST) and alanine aminotransferase (ALT) levels (Fig. 3d) and decreased hepatic vascular inflammatory infiltration (Figs. 4c and d). Notably, irregular dilation of myocardial blood vessels was observed in the CLP group but was absent in both the MIC and sham groups (Fig. S7a in Supporting information). No significant damage was detected in the kidneys or brain (Figs. S7b and c in Supporting information). Bacterial counts were significantly reduced in the blood and peritoneal fluid of MIC-treated mice (Figs. 4e and f).

  Figure 3

  

  Figure 3.  (a) Survival curves. Sepsis models were established using CLP. Survival was monitored until 7 days after the second administration (n = 7). (b) The anal temperature. Anal temperature change curves of mice after the second administration (n = 3). (c) The levels of IL-4, IL-6, IL-10, TGF-β1, and TNF-α in the serum were measured 24 h after the second administration (n = 3). (d) The levels of AST, ALT, creatinine, blood urea nitrogen (BUN), creatine kinase-MB (CK-MB), lactate dehydrogenase (LDH), nitric oxide (NO), and C-reactive protein (CRP) in the serum were measured 24 h after the second administration (n = 3). Data are presented as mean ± SD, ^*P < 0.05, ^**P < 0.01, ^***P < 0.001, ^****P < 0.0001.

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  Figure 4

  

  Figure 4.  MIC reduces organ damage and bacterial burden in CLP mice. (a) The results of the H&E staining of lung tissues from mice after the second administration for 24 h (the magnification is 400 ×, and the scale bar is 25 μm). (b) Lung damage score of H&E staining. (c) The results of the H&E staining of liver tissues from mice after the second administration for 24 h (the magnification is 400 ×, and the scale bar is 25 μm). (d) Liver damage score of H&E staining. (e) 24 h after the second administration, the mice were euthanized to obtain blood and peritoneal fluid (peritoneal fluid: approximately 2.5 mL of sterile cold physiological saline was injected into one side of the mice's abdominal cavity, and then the fluid was sucked back from the other side of the mice's abdominal cavity, which is called peritoneal fluid). Take 100 μL of blood and peritoneal fluid from each mouse separately and apply them to blood agar plates for bacterial culture. Representative images of bacteria counts in blood agar plates. (f) Representative images of Wright's stain of peritoneal fluid 24 h after the second administration (the magnification is 400 ×, and the scale bar is 25 μm) (n = 3). Data are presented as mean ± SD, ^*P < 0.05, ^**P < 0.01.

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  To determine whether MIC exerts immunomodulatory effects, immune cell profiles were analyzed 24 h after the second administration. Cells from the spleens and mesenteric lymph nodes (mLNs) were collected and subjected to flow cytometric analysis. The MIC-treated group exhibited significantly higher proportions and absolute numbers of B cells in the spleens (Fig. 5a) and mLNs (Fig. 5b) compared to the CLP and Sham groups. In contrast, the CLP group displayed increased neutrophil infiltration in the spleens (Fig. S8a in Supporting information) and mLNs (Fig. S9a in Supporting information), reflecting a heightened inflammatory response. MIC treatment significantly increased the macrophage population (Figs. S8b and S9b in Supporting information) while reducing the proportion and absolute number of regulatory T cells (Tregs) in the spleens (Fig. S8f in Supporting information) and mLNs (Fig. S9f in Supporting information). These findings suggest that MIC alleviates sepsis-induced immunosuppression and enhances immune function during sepsis.

  Figure 5

  

  Figure 5.  MIC treatment positively influences B cells in the spleens and mLNs of septic mice. The spleens and mLNs were harvested 24 h after the second administration. Flow cytometric quantification of B220⁺ B cell in (a) spleens and (b) mLNs (n = 3). Data are presented as mean ± SD, ^*P < 0.05, ^**P < 0.01, ^***P < 0.001, ^****P < 0.0001.

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  To investigate the effect of MIC on gene expression on B cells in vivo, we injected MIC into adult healthy mice and isolated B cells from their spleens. Cells purified from spleens were identified as B cells by flow cytometry (Fig. S10a in Supporting information). The mice B cells were used for RNA sequencing (RNA-seq). When comparing the MIC group to the Ctrl group, RNA-seq data showed 173 upregulated genes and 258 downregulated genes (Figs. S10b and c in Supporting information). Gene ontology (GO) analysis indicated that immune response-regulating cell surface receptor signaling pathway was among the most significantly affected functions by MIC treatment (Fig. S10d in Supporting information). Gene set enrichment analysis (GSEA) based on the KEGG database showed that MIC significantly influences genes involved in the Cytokine-cytokine receptor interaction, T cell receptor signaling pathway, and Intestinal immune network for IgA production (Fig. S10e in Supporting information). KEGG analysis further revealed that MIC significantly affects the Antigen processing and presentation and RIG-I-like receptor signaling pathway (Fig. S10f in Supporting information). These findings suggest that MIC affect immune functions and antibody secretion to combat sepsis.

  After discovering that MIC exerts its protective effects in sepsis by enhancing the humoral immune response, we investigated the direct impact of MIC on B cells using a human B lymphocyte cell line (Ramos). The optimal concentrations for stimulating Ramos B cells with Staphylococcus aureus protein A (SPA) and MIC were 0.1 and 14 μg/mL, respectively (Figs. S11a and b in Supporting information). MIC significantly enhanced B cell proliferation, as demonstrated by CFSE staining (Fig. 6a). Given that changes in proliferation and apoptosis are often accompanied by metabolic alterations, key markers of cellular metabolism were also assessed. MIC treatment led to increased cellular ATP levels and glucose consumption, while simultaneously decreasing lactate and pyruvate production (Fig. 6b). Interestingly, MIC stimulation did not increase the oxygen consumption rate (OCR) (Fig. 6c), but significantly reduced the extracellular acidification rate (ECAR) (Fig. 6d), leading to a marked increase in the OCR/ECAR ratio (Fig. 6e). These findings indicate that MIC promotes oxidative phosphorylation (OXPHOS) while inhibiting glycolysis, thereby increasing ATP production in B cells.

  Figure 6

  

  Figure 6.  MIC promotes proliferation, affects metabolism, and inhibits apoptosis in B cells. Ramos was stimulated using SPA, SPA mixed with MIC, MIC, and non-treated (PBS) for 48 h, respectively. (a) Cell proliferation using CFSE labeling by flow cytometry. (b) The levels of lactic acid, pyruvate, extracellular relative ATP, and glucose in cell supernatant. (c) The OCR was measured by an oxygen-sensitive probe for 150 min. (d) The ECAR was measured by incubation at 37 ℃ for 150 min. (e) A quantitative graph of the ratio of OCR to ECAR. (f) Apoptosis rate by flow cytometry using 7-AAD and Annexin V (n = 3). Data are presented as mean ± SD, ^*P < 0.05, ^**P < 0.01, ^***P < 0.001.

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  Apoptosis of B cells was measured by flow cytometry, and MIC treatment notably reduced the apoptosis rate compared to untreated cells (Fig. 6f). To further investigate the apoptotic pathway, expression levels of apoptosis-related proteins, including caspase-3, Bcl-2, Bcl-xl, Bax, and cytochrome c (Cyt C), were analyzed via Western blot (WB). In MIC-treated cells, the protein level of Bcl-2 and the Bcl-2/Bax ratio was increased, whereas Caspase-3 expression was decreased compared to untreated cells (Fig. S12 in Supporting information).

  Mitochondrial damage and excessive production of ROS play critical roles in driving the progression of sepsis [15, 16]. Thus, to explore how MIC affects mitochondrial function, ROS production and mitochondrial membrane potential (MMP) were assessed. MIC significantly reduced ROS levels and increased MMP in SPA-stimulated B cells (Figs. 7a and b).

  Figure 7

  

  Figure 7.  MIC alleviates mitochondrial dysfunction in B cells. Ramos was stimulated using SPA, SPA mixed with MIC, MIC, and non-treated (PBS) for 48 h, respectively. (a) ROS was detected by flow cytometry using DCFH-DA. (b) MMP was detected by flow cytometry using JC-1. (c) Sub-cellular morphology was observed by TEM. Scale bars, 2 µm (up) and 1 µm (down). (d) Cells were incubated for 20 min at 37 ℃ with 25 nmol/L Deep Red-Fluorescent Mitotracker. Mitochondria (red spot) were observed by a laser confocal microscope (Scale bar, 10 µm). (e) The expression levels of MFN1, MFN2, OPA1, DRP1, and FIS1 were measured using WB analysis. Relative intensities were quantitated by densitometry using ImageJ and normalized to GAPDH levels. n = 3. Data are presented as mean ± SD, ^*P < 0.05, ^**P < 0.01, ^***P < 0.001.

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  Sub-cellular morphology was analyzed using transmission electron microscopy (TEM). TEM images revealed lipid droplet accumulation on the cell surface following SPA and/or MIC stimulation; however, MIC treatment significantly reduced the number of lipid droplets (Fig. 7c), suggesting that MIC may mitigate cellular response induced by SPA stimulation. Moreover, SPA stimulation caused blurring of mitochondrial membrane boundaries, while MIC treatment was associated with an increased number of mitochondria and enhanced mitochondrial integrity (Figs. 7c and d).

  Given that MIC treatment enhanced mitochondrial biogenesis, mitochondrial membrane dynamics proteins were analyzed via WB. MIC treatment groups exhibited increased levels of optic atrophy protein 1 (OPA1) and mitochondrial fission 1 (FIS1), along with decreased levels of mitofusin 1 (MFN1) and MFN2, while dynamin-related protein 1 (DRP1) levels remained largely unchanged (Fig. 7e). Notably, the MIC-treated group also demonstrated significant expansion of the Golgi apparatus, which may correlate with the enhanced antibody secretion observed earlier (Fig. 7c).

  To investigate the effects of MIC on B cells in greater detail, RNA-seq was performed on B cells stimulated with MIC or PBS (NCBI SRA repository, PRJNA1183558). The RNA-seq data identified 61 upregulated genes and 65 downregulated genes when comparing the MIC group to the PBS (Ctrl) group (Figs. S13a and b in Supporting information). GO analysis indicated that humoral immunity and anti-inflammatory responses were among the most significantly affected functions by MIC treatment (Fig. S13c in Supporting information). GSEA based on the KEGG database showed that MIC significantly influences genes involved in the OXPHOS pathway, indicating an impact on cellular metabolism (Fig. S13d in Supporting information). KEGG analysis further revealed that MIC significantly affects the NF-κB pathway, which is associated with infection and inflammation, as well as the RIG-I-like receptor signaling pathway, which is linked to antibody secretion (Fig. S13e in Supporting information). These findings suggest that MIC enhances anti-infection mechanisms and antibody secretion to combat sepsis.

  RNA-seq results were corroborated by WB and reverse transcription quantitative PCR (RT-qPCR). WB confirmed that MIC activated NF-κB signaling under infection conditions (SPA stimulation) but not in isolation (Fig. S13f in Supporting information). MIC treatment also increased the expression of OASL, MAVS, and BIRC2 in the RIG-I pathway while reducing pro-inflammatory gene expression in the NF-κB pathway (Figs. S14a and b in Supporting information). While OXPHOS pathway genes were not significantly altered (Fig. S14c in Supporting information), MIC increased ATP6V1B1 expression and reduced CYCS, GALM, and LDHAL6B expression (Figs. S15a and b in Supporting information).

  Sepsis remains a leading cause of mortality worldwide, primarily due to dysregulated immune responses and organ dysfunction [10, 17]. Our study provides compelling evidence that MIC treatment restores humoral immunity and mitochondrial function in B cells, mitigating systemic inflammation and improving survival in a CLP-induced sepsis model. These findings highlight the potential of MIC as a novel therapeutic strategy for sepsis management, particularly in addressing the often-overlooked immunosuppressive phase that follows initial hyperinflammation. If validated in further preclinical and clinical studies, MIC could fill a critical gap in current therapeutic options by providing a means to restore immune competence in septic patients, thereby reducing late-stage mortality due to secondary infections.

  Low levels of immunoglobulins are associated with poor prognoses in sepsis [18]. While some studies have reported positive outcomes using immunoglobulin preparations enriched with IgA, IgG, or IgM, controversies remain regarding the side effect of intravenous immunoglobulin as passive immunity against sepsis [17, 19, 20]. Nevertheless, naturally occurring catalytic antibodies demonstrate microbial defense functions against a broad range of pathogens [21, 22]. Sepsis can be considered a race to the death between pathogens and the host immune system, the invasion of pathogens lead to multifaceted immune dysregulation [10, 17, 23], including early hyperinflammation causing organ damage [24, 25], and subsequent immunosuppression linked to immune cell depletion, highlighting the critical role of rapid pathogen clearance in restoring immune homeostasis. Antibodies play an important role in clearing infection and regulating immunity, and MIC is precisely through enhancing the production of antibodies to rapidly clear invading pathogens. The ability is crucial for restoring septic immune system homeostasis, which can lead to improved therapeutic outcomes.

  During inflammation, immune cells such as B cells require continuous metabolic adaptation to sustain adequate host defense [26]. An imbalance in B cells metabolism has been proposed as one of the potential mechanisms underlying sepsis-associated immune dysfunction [27, 28]. Sepsis-induced metabolic perturbations in B cells, marked by hyperactivated glycolysis, mitochondrial fragmentation, and lactate accumulation [29]. Increased lactate metabolism is linked with acidic intracellular pH and the upregulation of apoptosis during an immune response [30]. During sepsis, metabolic reprogramming disrupts B cells's survival and functional homeostasis [31]. B cells metabolism-dysfunction aggravate systemic inflammatory response and mitochondrial oxidative damage in multiple organs, ultimately leading to organ dysfunction such as acute lung injury and tubular epithelial cell necrosis. The immune dysregulation observed in sepsis is also characterized by an abnormally high apoptosis rate of immune cells such as B cells [10, 17, 32]. We observed that MIC activates B cells to promote OXPHOS and ATP production, and suppress the apoptosis of the cells. This observation suggests that MIC treatment could confer beneficial effects against sepsis-induced immune dysregulation, potentially preventing patients from opportunistic infections.

  In summary, we have developed an efficient inorganic anionic oligomeric nanocluster, termed MIC, which displays notable chaotropic behavior upon interaction with organic substrates, establishing it as a promising therapeutic candidate for sepsis. Unlike conventional metal-based antibacterial materials, MIC does not exhibit direct antibacterial properties. Instead, our in vitro findings demonstrate that MIC directly activates B lymphocytes, thereby addressing both immune and metabolic dysfunction. Through the humoral immune response, polyclonal immunoglobulins secreted by activated B lymphocytes play a pivotal role in pathogen clearance during sepsis. Given the acute and systemic nature of sepsis, and the frequent impairment of consciousness in affected patients, intravenous administration of MIC represents the most clinically suitable route, enabling rapid and effective therapeutic delivery. Thus, MIC's mechanism may reduce reliance on traditional antimicrobial therapies and potentially circumvent the development of drug resistance. This work not only provides deeper insight into the interplay between MIC and immune cells but also lays a foundation for the translation of MIC into a potent, life-saving intervention for patients with sepsis.

  Declaration of Interest Statement

  The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

  CRediT authorship contribution statement

  Ying Wang: Validation, Methodology, Investigation. Jiaqi Lv: Validation, Methodology, Investigation. Song Liang: Writing – review & editing, Methodology. Yingdong Xie: Writing – review & editing, Investigation. Yuan Tian: Writing – review & editing, Investigation. Dong Li: Writing – review & editing, Conceptualization. Hong-Ying Zang: Writing – review & editing, Conceptualization.

  Acknowledgments

  We gratefully acknowledge the generous supported by the National Key R & D Program of China (No. 2023YFC2413100), the National Natural Science Foundation of China (Nos. 22322102, 21871042 and 21471028), the Fundamental Research Funds for the Central Universities-Excellent Youth Team Program (No. 2412023YQ001), the Natural Science Foundation of Jilin Province (Nos. YDZJ202401550ZYTS, 20200201083JC). We gratefully acknowledge the Key Laboratory of Pathology and Biology, Ministry of Education, Jilin University.

  Supplementary materials

  Supplementary material associated with this article can be found, in the online version, at doi:10.1016/j.cclet.2025.111455.

  
  
• 1. [1]

     T.P. Dasari, K. Pathakoti, H.M. Hwang, J. Environ. Sci. 25 (2013) 882–888.

  2. [2]

     S. Ma, M. Zhang, J. Nie, et al., Carbohyd. Polym. 203 (2019) 415–422.

  3. [3]

     Y. Zhong, X.T. Zheng, S. Zhao, X. Su, X.J. Loh, ACS Nano 16 (2022) 19840–19872. doi: 10.1021/acsnano.2c08262

  4. [4]

     B.K. Gaiser, T.F. Fernandes, M. Jepson, et al., Environ. Health: A Global Access Sci. Source 8 (2009) S2. doi: 10.1186/1476-069X-8-S1-S2

  5. [5]

     N. Hadrup, A.K. Sharma, N.R. Jacobsen, K. Loeschner, Drug Chem. Toxicol. 45 (2022) 2388–2397. doi: 10.1080/01480545.2021.1950167

  6. [6]

     M. Singer, C.S. Deutschman, C.W. Seymour, et al., JAMA 315 (2016) 801–810. doi: 10.1001/jama.2016.0287

  7. [7]

     L. Evans, A. Rhodes, W. Alhazzani, et al., Intensive Care Med. 47 (2021) 1181–1247. doi: 10.1007/s00134-021-06506-y

  8. [8]

     L. Lu, L. Quan, J. Li, et al., J. Nanobiotechnol. 21 (2023) 170.

  9. [9]

     T. van der Poll, F.L. van de Veerdonk, B.P. Scicluna, M.G. Netea, Nat. Rev. Immunol. 17 (2017) 407–420. doi: 10.1038/nri.2017.36

  10. [10]

      T. van der Poll, M. Shankar-Hari, W.J. Wiersinga, Immunity 54 (2021) 2450–2464.

  11. [11]

      B. Qiu, L. Cai, Y. Wang, et al., Mater. Today Energy 11 (2019) 89–96.

  12. [12]

      J.Q. Lv, B. Li, Q. Liu, et al., Angew. Chem. Int. Ed. 62 (2023) e202306193.

  13. [13]

      A. Shavel, B. Rodríguez-González, M. Spasova, M. Farle, L.M. Liz-Marzán, Adv. Funct. Mater. 17 (2007) 3870–3876. doi: 10.1002/adfm.200700494

  14. [14]

      Z.M. Zhang, Y.G. Li, S. Yao, et al., Angew. Chem. Int. Ed. 48 (2009) 1581–1584. doi: 10.1002/anie.200805827

  15. [15]

      D. Hu, H. Sheeja Prabhakaran, Y.Y. Zhang, et al., Critical Care 28 (2024) 292.

  16. [16]

      Bushra, S.I.A., S. Begum, et al., Mitochondrion 79 (2024) 101967.

  17. [17]

      M. Cao, G. Wang, J. Xie, Cell Death Discov. 9 (2023) 465.

  18. [18]

      J.F. Bermejo-Martin, E.J. Giamarellos-Bourboulis, Int. J. Antimicrobial. Agents 46 (2015) S25–S28.

  19. [19]

      K. Werdan, G. Pilz, O. Bujdoso, et al., Crit. Care Med. 35 (2007) 2693–2701.

  20. [20]

      M. Akatsuka, Y. Masuda, H. Tatsumi, T. Sonoda, Clin Ther 44 (2022) 295–303.

  21. [21]

      A. Bowen, M. Wear, A. Casadevall, Infection Immunity 85 (2017) e00202–00217.

  22. [22]

      S. Paul, S.A. Planque, Y. Nishiyama, C.V. Hanson, R.J. Massey, Adv. Experim. Medicine Biol. 750 (2012) 56–75. doi: 10.1007/978-1-4614-3461-0_5

  23. [23]

      M.J. Delano, P.A. Ward, J. Clinical Investigation 126 (2016) 23–31.

  24. [24]

      D.C. Angus, S. Opal, Jama 315 (2016) 1457–1459. doi: 10.1001/jama.2016.2762

  25. [25]

      J.D. Faix, Crit. Rev. Clin. Lab Sci. 50 (2013) 23–36. doi: 10.3109/10408363.2013.764490

  26. [26]

      S. Preau, D. Vodovar, B. Jung, et al., Annal. Intensive Care 11 (2021) 104.

  27. [27]

      D.L. Williams, C. Li, E.R. Sherwood, J. Leukoc Biol. 106 (2019) 7–9. doi: 10.1002/jlb.4ce0319-100r

  28. [28]

      I. Grondman, R.J.W. Arts, R.M. Koch, et al., J. Leukoc Biol. 106 (2019) 11–25. doi: 10.1002/jlb.5hi0119-018r

  29. [29]

      L.R. Waters, F.M. Ahsan, D.M. Wolf, O. Shirihai, M.A. Teitell, iScience 5 (2018) 99–109.

  30. [30]

      O.T.M. Bucheli, D. Rodrigues, K. Portmann, et al., Sci. Rep. 14 (2024) 8507.

  31. [31]

      N.M. Chapman, H. Chi, Immunity 55 (2022) 14–30.

  32. [32]

      J. Chen, H. Wei, Front. Pharmacol. 12 (2021) 718089.

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  Figure 1  (a) Polyhedral and ball-stick configurations of sample MIC. Fe: blue; O: red; C: dark grey. (b, c) MIC space-filling representations. (d) Zeta potential of MIC (n = 3). (e) SAXS spectra of MIC aqueous solution (the red line represents the SAXS of MIC after 12 h of dissolution in aqueous solution, and the black line represents the initial state) (n = 3).

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  Figure 2  MIC boosts humoral immunity to eliminate bacteria. (a) Representative images of bacterial culture of bacterial solution mixed with Sprague-Dawley rats' serum after different treatments. (b) Measure the OD₆₀₀ of a mixed solution with a colony count greater than 300. OD₆₀₀ of bacterial solution (dilution 1:100) equal volume mixed with serum. (c) Bacteria counts of LB agar medium after bacterial solution (dilution 1:10⁶) equal volume mixed with serum. (d) Bacteria counts of LB agar medium after bacterial solution (dilution 1:10⁶) equal volume mixed with serum (dilution 1:10). The levels of (e) IgM, (f) IgG, and (g) IgA in the serum of Sprague-Dawley rats after different administrations. n = 3. Data are presented as mean ± SD, ^*P < 0.05, ^**P < 0.01, ^***P < 0.001.

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  Figure 3  (a) Survival curves. Sepsis models were established using CLP. Survival was monitored until 7 days after the second administration (n = 7). (b) The anal temperature. Anal temperature change curves of mice after the second administration (n = 3). (c) The levels of IL-4, IL-6, IL-10, TGF-β1, and TNF-α in the serum were measured 24 h after the second administration (n = 3). (d) The levels of AST, ALT, creatinine, blood urea nitrogen (BUN), creatine kinase-MB (CK-MB), lactate dehydrogenase (LDH), nitric oxide (NO), and C-reactive protein (CRP) in the serum were measured 24 h after the second administration (n = 3). Data are presented as mean ± SD, ^*P < 0.05, ^**P < 0.01, ^***P < 0.001, ^****P < 0.0001.

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  Figure 4  MIC reduces organ damage and bacterial burden in CLP mice. (a) The results of the H&E staining of lung tissues from mice after the second administration for 24 h (the magnification is 400 ×, and the scale bar is 25 μm). (b) Lung damage score of H&E staining. (c) The results of the H&E staining of liver tissues from mice after the second administration for 24 h (the magnification is 400 ×, and the scale bar is 25 μm). (d) Liver damage score of H&E staining. (e) 24 h after the second administration, the mice were euthanized to obtain blood and peritoneal fluid (peritoneal fluid: approximately 2.5 mL of sterile cold physiological saline was injected into one side of the mice's abdominal cavity, and then the fluid was sucked back from the other side of the mice's abdominal cavity, which is called peritoneal fluid). Take 100 μL of blood and peritoneal fluid from each mouse separately and apply them to blood agar plates for bacterial culture. Representative images of bacteria counts in blood agar plates. (f) Representative images of Wright's stain of peritoneal fluid 24 h after the second administration (the magnification is 400 ×, and the scale bar is 25 μm) (n = 3). Data are presented as mean ± SD, ^*P < 0.05, ^**P < 0.01.

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  Figure 5  MIC treatment positively influences B cells in the spleens and mLNs of septic mice. The spleens and mLNs were harvested 24 h after the second administration. Flow cytometric quantification of B220⁺ B cell in (a) spleens and (b) mLNs (n = 3). Data are presented as mean ± SD, ^*P < 0.05, ^**P < 0.01, ^***P < 0.001, ^****P < 0.0001.

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  Figure 6  MIC promotes proliferation, affects metabolism, and inhibits apoptosis in B cells. Ramos was stimulated using SPA, SPA mixed with MIC, MIC, and non-treated (PBS) for 48 h, respectively. (a) Cell proliferation using CFSE labeling by flow cytometry. (b) The levels of lactic acid, pyruvate, extracellular relative ATP, and glucose in cell supernatant. (c) The OCR was measured by an oxygen-sensitive probe for 150 min. (d) The ECAR was measured by incubation at 37 ℃ for 150 min. (e) A quantitative graph of the ratio of OCR to ECAR. (f) Apoptosis rate by flow cytometry using 7-AAD and Annexin V (n = 3). Data are presented as mean ± SD, ^*P < 0.05, ^**P < 0.01, ^***P < 0.001.

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  Figure 7  MIC alleviates mitochondrial dysfunction in B cells. Ramos was stimulated using SPA, SPA mixed with MIC, MIC, and non-treated (PBS) for 48 h, respectively. (a) ROS was detected by flow cytometry using DCFH-DA. (b) MMP was detected by flow cytometry using JC-1. (c) Sub-cellular morphology was observed by TEM. Scale bars, 2 µm (up) and 1 µm (down). (d) Cells were incubated for 20 min at 37 ℃ with 25 nmol/L Deep Red-Fluorescent Mitotracker. Mitochondria (red spot) were observed by a laser confocal microscope (Scale bar, 10 µm). (e) The expression levels of MFN1, MFN2, OPA1, DRP1, and FIS1 were measured using WB analysis. Relative intensities were quantitated by densitometry using ImageJ and normalized to GAPDH levels. n = 3. Data are presented as mean ± SD, ^*P < 0.05, ^**P < 0.01, ^***P < 0.001.

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