human s100a8  (Elabscience Biotechnology)

Journal: JID Innovations

Article Title: A neuroimmune axis linking S100A8/9 to itch sensitization in both bullous pemphigoid and atopic dermatitis

doi: 10.1016/j.xjidi.2026.100470

Figure Lengend Snippet: Increased S100A8/9 expression in the skin and serum of patients with BP and AD. ( a ) Immunohistochemical analysis with anti-S100A8/9 antibody showing the expression of S100A8/9 in keratinocytes and infiltrating inflammatory cells of lesional skin of patients with BP and AD. S100A8/9 expression was not observed in the healthy skin. Scale bar: 100 μm. (b) Quantification of the expression level of S100A8/9. (control, n = 2; BP, n = 5; AD n = 2). Inter-patient heterogeneity of the expression level of S100A8/9 was observed in the BP skin samples, and representative images of both low and high S100A8/9 expression were shown in A. (c) ELISA analysis showing increased S100A8/9 concentrations in the serum of patients with BP. (control, n = 8; BP, n = 16; P = .0087, Mann-Whitney test). Data are reported as mean ± SD. AD, atopic dermatitis; BP, bullous pemphigoid.

Article Snippet: Five-micrometer paraffin sections were collected and stained for immunohistochemistry with anti-S100A8 antibody (1:8000, R&D Systems, MAB4570).

Techniques: Expressing, Immunohistochemical staining, Control, Enzyme-linked Immunosorbent Assay, MANN-WHITNEY

Journal: JID Innovations

Article Title: A neuroimmune axis linking S100A8/9 to itch sensitization in both bullous pemphigoid and atopic dermatitis

doi: 10.1016/j.xjidi.2026.100470

Figure Lengend Snippet: S100A8/9 directly activates small-diameter, nociceptive DRG sensory neurons. ( a ) Representative fluorescent images of cultured DRG sensory neurons isolated from Pirt GCaMP3/+ mice before and after S100A8/9 (100 ng/ml) application. Arrows point to sensory neurons showing increased GCaMP3 fluorescence levels after S100A8/9 application. (b) Histogram showing size distribution of S100A8/9-responsive neurons. (c–e) Representative traces of DRG neurons evoked by indicated chemicals, including S100A8/9 (100 ng/ml), S100A8 (100 ng/ml), S100A9 (100 ng/ml), capsaicin (1 μM), and KCl (75 mM) in a calcium imaging assay. All S100A8/9-sensitive neurons responded to capsaicin and KCl. The majority of S100A8- and S100A9-responsive neurons also responded to S100A8/9. The three different colors (Red, Green, and Blue) represent individual cells in C-E. (f) TAK-242 inhibited S100A8/9-induced calcium responses in sensory neurons. (n = 3 for both groups P = .018, Welch’s t -test). Data are reported as mean ± SD. AD, atopic dermatitis; BP, bullous pemphigoid; DRG, dorsal root ganglia.

Article Snippet: Five-micrometer paraffin sections were collected and stained for immunohistochemistry with anti-S100A8 antibody (1:8000, R&D Systems, MAB4570).

Techniques: Cell Culture, Isolation, Fluorescence, Imaging

Journal: JID Innovations

Article Title: A neuroimmune axis linking S100A8/9 to itch sensitization in both bullous pemphigoid and atopic dermatitis

doi: 10.1016/j.xjidi.2026.100470

Figure Lengend Snippet: S100A8/9 potentiate histamine-induced itch. ( a ) Subcutaneous injection of S100A8/9 (20 μg/ml) into the nape of the neck of wild-type mice does not induce scratching behavior. (n = 7 for both groups, P = .97, Welch’s t test). (b) Co-injection of S100A8/9 increased histamine (20 mM)-induced scratching behavior. (n = 11 for both groups, P = .038, Welch’s t test). Data are reported as mean ± SD.

Article Snippet: Five-micrometer paraffin sections were collected and stained for immunohistochemistry with anti-S100A8 antibody (1:8000, R&D Systems, MAB4570).

Techniques: Injection

Journal: Frontiers in Pediatrics

Article Title: Noninvasive salivary biomarkers (PTX3, calprotectin, and IL-8) for early-onset neonatal pneumonia: case-control differences and exploratory discrimination

doi: 10.3389/fped.2026.1747967

Figure Lengend Snippet: Salivary PTX3, calprotectin, and IL-8 are elevated in early-onset neonatal pneumonia (EONP) and show strong case—control discrimination. (A – C) Distributions of salivary PTX3, calprotectin, and IL-8 in EONP vs. healthy controls (medians with IQRs; Mann–Whitney tests, all P < 0.001). (D – F) ROC curves for each single biomarker with optimal cutoffs (PTX3 ≥ 1.38 ng/mL; calprotectin ≥5.49 ng/mL; IL-8 ≥ 8.69 pg/mL). The solid line denotes the ROC curve and the dashed lines indicate the 95% confidence interval (lower and upper limits). (G) ROC curves for the three-marker combined model (logistic regression using PTX3, calprotectin, and IL-8). The combined model achieved an apparent AUC of 0.978, and internally validated performance is overlaid (LOOCV and 5-fold cross-validation), demonstrating minimal performance degradation.

Article Snippet: Salivary PTX3, calprotectin, and IL-8 concentrations were measured using commercial ELISA kits according to the manufacturers' instructions: PTX3 with the QuantikineTM Human Pentraxin 3 Immunoassay (R&D Systems, Cat. DPTX30B); calprotectin with the Quantikine® Human Calprotectin Heterodimer Immunoassay (R&D Systems, Cat. DS8900); and IL-8 with the LEGEND MAXTM High Sensitivity Human IL-8 ELISA Kit (BioLegend, Cat. 431517).

Techniques: Control, MANN-WHITNEY, Biomarker Discovery, Marker

Journal: Frontiers in Pediatrics

Article Title: Noninvasive salivary biomarkers (PTX3, calprotectin, and IL-8) for early-onset neonatal pneumonia: case-control differences and exploratory discrimination

doi: 10.3389/fped.2026.1747967

Figure Lengend Snippet: Salivary biomarkers are inter-correlated and track systemic inflammation in EONP. (A) Pairwise correlations among salivary PTX3, calprotectin, and IL-8 in EONP (Spearman r , all P < 0.001). (B) Corresponding correlations in healthy controls (all P > 0.05). (C) Heatmap of Spearman correlations between salivary biomarkers and systemic indices (hs-CRP, serum PCT, serum IL-6, WBC, ANC, I/T ratio, platelets) in EONP, showing moderate-to-strong positive associations with inflammatory markers and inverse associations with platelets (panel labels show exact r ).

Article Snippet: Salivary PTX3, calprotectin, and IL-8 concentrations were measured using commercial ELISA kits according to the manufacturers' instructions: PTX3 with the QuantikineTM Human Pentraxin 3 Immunoassay (R&D Systems, Cat. DPTX30B); calprotectin with the Quantikine® Human Calprotectin Heterodimer Immunoassay (R&D Systems, Cat. DS8900); and IL-8 with the LEGEND MAXTM High Sensitivity Human IL-8 ELISA Kit (BioLegend, Cat. 431517).

Techniques:

Journal: Frontiers in Pediatrics

Article Title: Noninvasive salivary biomarkers (PTX3, calprotectin, and IL-8) for early-onset neonatal pneumonia: case-control differences and exploratory discrimination

doi: 10.3389/fped.2026.1747967

Figure Lengend Snippet: Salivary biomarkers modestly enrich for blood-culture-positive bacteremia within EONP. (A – C) Salivary PTX3, calprotectin, and IL-8 in culture-positive vs. culture-negative EONP cases (medians with IQRs; Mann–Whitney P < 0.001, =0.003, =0.002, respectively). (D – F) ROC curves for bacteremia detection using single salivary markers with optimal cutoffs (PTX3 ≥ 2.51 ng/mL; calprotectin ≥14.57 ng/mL; IL-8 ≥ 18.97 pg/mL), yielding AUCs 0.725, 0.682, and 0.689, respectively. The solid line denotes the ROC curve and the dashed lines indicate the 95% confidence interval (lower and upper limits). (G) ROC curves for the three-marker combined model (logistic regression using PTX3, calprotectin, and IL-8). The combined model achieved an apparent AUC of 0.702, with internally validated AUCs of 0.706 (5-fold cross-validation) and 0.702 (LOOCV), indicating stable but moderate enrichment performance.

Article Snippet: Salivary PTX3, calprotectin, and IL-8 concentrations were measured using commercial ELISA kits according to the manufacturers' instructions: PTX3 with the QuantikineTM Human Pentraxin 3 Immunoassay (R&D Systems, Cat. DPTX30B); calprotectin with the Quantikine® Human Calprotectin Heterodimer Immunoassay (R&D Systems, Cat. DS8900); and IL-8 with the LEGEND MAXTM High Sensitivity Human IL-8 ELISA Kit (BioLegend, Cat. 431517).

Techniques: MANN-WHITNEY, Marker, Biomarker Discovery

Journal: Frontiers in Microbiology

Article Title: Klebsiella pneumoniae infection induces an S100A8/A9-mediated autocrine loop in human airway epithelium to amplify inflammation

doi: 10.3389/fmicb.2026.1768140

Figure Lengend Snippet: Klebsiella pneumoniae infection directly induces S100A8/A9 expression and secretion in HBE cells. Primary HBE cells were infected with WT K. pneumoniae or an isogenic acapsular mutant (Δ cps ). (A,B) Expression of S100A8 and S100A9 was determined by qRT-PCR at 8 h post-infection with various MOIs of K. pneumoniae , or 100 MOI K. pneumoniae for 4–12 h (C,D) . Data are normalized to the housekeeping gene GAPDH and expressed as fold change relative to uninfected control cells. (E) Secretion of S100A8/A9 heterodimer induced by WT K. pneumoniae and the isogenic Δ cps mutant at indicated MOIs after 24 h. All data are presented as mean ± SEM of three independent experiments. * p < 0.05, ** p < 0.01 vs. uninfected cells (A–D) . Statistical differences between the WT and Δ cps groups were determined by Two-way ANOVA followed by Tukey’s post-hoc test. * p < 0.05 compared between strains at the same MOI (E) .

Article Snippet: The concentrations of secreted S100A8/A9 heterodimer, IL-8, and IL-6 were quantified by commercial Quantikine ELISA kits (R&D Systems, Cat# DS8900 for S100A8/A9, D8000C for IL-8, and D6050B for IL-6).

Techniques: Infection, Expressing, Mutagenesis, Quantitative RT-PCR, Control

Journal: Frontiers in Microbiology

Article Title: Klebsiella pneumoniae infection induces an S100A8/A9-mediated autocrine loop in human airway epithelium to amplify inflammation

doi: 10.3389/fmicb.2026.1768140

Figure Lengend Snippet: Extracellular S100A8/A9 functions as a potent pro-inflammatory stimulus for primary HBE cells. (A) Primary HBE cells were infected with WT K. pneumoniae (MOI 100) for the indicated time points. Relative mRNA expression of TLR4 was determined by qRT-PCR, with data calibrated to GAPDH and shown as fold induction over the baseline (0 h). (B) Representative western blot showing total TLR4 protein levels. β -Actin served as the housekeeping protein. (C) Quantification of TLR4 protein expression from three independent replicates, with values standardized to β-Actin. (D,E) HBE cells were treated for 24 h with the specified doses of endotoxin-free recombinant human S100A8/A9 (rS100A8/A9). The release of (D) IL-8 and (E) IL-6 was detected by ELISA. Data are presented as mean ± SEM of three independent experiments. * p < 0.05 versus the untreated control (A,C,D,E) .

Article Snippet: The concentrations of secreted S100A8/A9 heterodimer, IL-8, and IL-6 were quantified by commercial Quantikine ELISA kits (R&D Systems, Cat# DS8900 for S100A8/A9, D8000C for IL-8, and D6050B for IL-6).

Techniques: Infection, Expressing, Quantitative RT-PCR, Western Blot, Recombinant, Enzyme-linked Immunosorbent Assay, Control

Journal: Frontiers in Microbiology

Article Title: Klebsiella pneumoniae infection induces an S100A8/A9-mediated autocrine loop in human airway epithelium to amplify inflammation

doi: 10.3389/fmicb.2026.1768140

Figure Lengend Snippet: Epithelial-derived S100A8/A9 is functionally required for the full inflammatory response to K. pneumoniae infection. Primary HBE cells were transfected with control siRNA (siCtrl) or S100A9 siRNA (siA9). (A) Knockdown efficiency was confirmed 48 h post-transfection by qRT-PCR analysis of S100A9 mRNA levels following a 12-h infection with WT K. pneumoniae (MOI 100), negative values represent fold reduction calculated as the negative inverse of 2 −ΔΔCt following the Schmittgen and Livak protocol. (B) Functional knockdown was confirmed by measuring S100A8/A9 protein secretion by ELISA in supernatants from infected cells at 24 h. (C,D) Control and S100A9 -deficient cells were infected with WT K. pneumoniae (MOI 100) for 24 h, and the secretion of cytokines were quantified by ELISA. Data are presented as mean ± SEM of three independent experiments. * p < 0.05 vs. Kp + siCtrl (A,B) or uninfected cells (C,D) , # p < 0.05 vs. Kp + siCtrl (C,D) .

Article Snippet: The concentrations of secreted S100A8/A9 heterodimer, IL-8, and IL-6 were quantified by commercial Quantikine ELISA kits (R&D Systems, Cat# DS8900 for S100A8/A9, D8000C for IL-8, and D6050B for IL-6).

Techniques: Derivative Assay, Infection, Transfection, Control, Knockdown, Quantitative RT-PCR, Functional Assay, Enzyme-linked Immunosorbent Assay

Journal: Frontiers in Microbiology

Article Title: Klebsiella pneumoniae infection induces an S100A8/A9-mediated autocrine loop in human airway epithelium to amplify inflammation

doi: 10.3389/fmicb.2026.1768140

Figure Lengend Snippet: TLR4 is the essential receptor mediating S100A8/A9-induced inflammation in HBE cells during K. pneumoniae infection. (A,B) HBE cells were pre-incubated with neutralizing antibodies against TLR4 (10 μg/mL), RAGE (100 μg/mL), or an isotype control (Iso Ctrl) for 1 h, followed by stimulation with recombinant human S100A8/A9 (20 μg/mL) for 24 h. Levels of (A) IL-8 and (B) IL-6 in supernatants were determined by ELISA. (C,D) HBE cells were pre-treated with the indicated antibodies for 1 h and subsequently infected with WT K. pneumoniae (MOI 100) for 24 h. Secretion of (C) IL-8 and (D) IL-6 was quantified by ELISA. All results are expressed as mean ± SEM of three independent experiments. * p < 0.05 compared with the indicated groups.

Article Snippet: The concentrations of secreted S100A8/A9 heterodimer, IL-8, and IL-6 were quantified by commercial Quantikine ELISA kits (R&D Systems, Cat# DS8900 for S100A8/A9, D8000C for IL-8, and D6050B for IL-6).

Techniques: Infection, Incubation, Control, Recombinant, Enzyme-linked Immunosorbent Assay

Journal: Frontiers in Microbiology

Article Title: Klebsiella pneumoniae infection induces an S100A8/A9-mediated autocrine loop in human airway epithelium to amplify inflammation

doi: 10.3389/fmicb.2026.1768140

Figure Lengend Snippet: The S100A8/A9 autocrine loop drives NF-κB activation and subsequent cytokine release in HBE cells. (A) Representative immunoblots showing degradation of IκBα in primary HBE cells stimulated with rS100A8/A9 (20 μg/mL) for 60 min. β-Actin served as a loading control. (B) Densitometric quantification of IκBα protein levels from (A) . (C) Representative immunofluorescence images showing subcellular localization of the p65 subunit (green) at 60 min post-stimulation with rS100A8/A9. Nuclei were counterstained with DAPI (blue). (D) HBE cells were transfected with control siRNA (siCtrl) or siRNA targeting S100A9 (siS100A9) and subsequently infected with wild-type K. pneumoniae (MOI 100). Representative immunoblots of IκBα levels are shown at 60 min post-infection. (E) Densitometric quantification of IκBα degradation from (D) . (F) Representative immunofluorescence images showing p65 localization (green) in siCtrl- or siS100A9-transfected HBE cells at 60 min post- K. pneumoniae infection. Nuclei were stained with DAPI (blue). (G) Secretion of IL-8 and IL-6 by HBE cells. Cells were pre-treated with or without the NF-κB inhibitor BAY 11–7,082 (10 μM) for 60 min, followed by stimulation with rS100A8/A9 (20 μg/mL) for 24 h. Cytokine levels in supernatants were measured by ELISA. All graphs display mean ± SEM, * p < 0.05 compared with the untreated control (B,E,G) ; # p < 0.05 compared with siCtrl + Kp or the S100A8/A9-stimulated group without inhibitor (E,G) .

Article Snippet: The concentrations of secreted S100A8/A9 heterodimer, IL-8, and IL-6 were quantified by commercial Quantikine ELISA kits (R&D Systems, Cat# DS8900 for S100A8/A9, D8000C for IL-8, and D6050B for IL-6).

Techniques: Activation Assay, Western Blot, Control, Immunofluorescence, Transfection, Infection, Staining, Enzyme-linked Immunosorbent Assay

Journal: Frontiers in Microbiology

Article Title: Klebsiella pneumoniae infection induces an S100A8/A9-mediated autocrine loop in human airway epithelium to amplify inflammation

doi: 10.3389/fmicb.2026.1768140

Figure Lengend Snippet: The epithelial S100A8/A9 autocrine loop is a critical driver of neutrophil chemotaxis in response to K. pneumoniae infection. Neutrophil chemotaxis was assessed using a Transwell assay. (A) Comparison of the chemotactic activity of supernatants from uninfected HBE cells (conditioned medium, CM), HBE cells infected with WT K. pneumoniae (MOI 100), and fMLP (positive control) on primary human neutrophils. (B) Comparison of the chemotactic activity of supernatants from infected control (siCtrl) HBE cells versus infected S100A9-deficient (siS100A9) HBE cells. Flow cytometry was used to determine the absolute number of migrated neutrophils. Data are shown as mean ± SEM from three separate experiments. * p < 0.05 vs. uninfected CM, # p < 0.05 vs. Kp + siCtrl.

Article Snippet: The concentrations of secreted S100A8/A9 heterodimer, IL-8, and IL-6 were quantified by commercial Quantikine ELISA kits (R&D Systems, Cat# DS8900 for S100A8/A9, D8000C for IL-8, and D6050B for IL-6).

Techniques: Chemotaxis Assay, Infection, Transwell Assay, Comparison, Activity Assay, Positive Control, Control, Flow Cytometry

Journal: Frontiers in Microbiology

Article Title: Klebsiella pneumoniae infection induces an S100A8/A9-mediated autocrine loop in human airway epithelium to amplify inflammation

doi: 10.3389/fmicb.2026.1768140

Figure Lengend Snippet: Proposed model of the S100A8/A9-mediated autocrine amplification loop in human airway epithelial cells during K. pneumoniae infection. Initial recognition of encapsulated K. pneumoniae by the airway epithelium triggers a primary transcriptional response, leading to the synthesis and secretion of the alarmin S100A8/A9 and a simultaneous upregulation of its cognate receptor, TLR4. This dual mechanism creates a primed state within the epithelium. The endogenously produced S100A8/A9 then acts back on the enriched TLR4 receptors in an autocrine or paracrine manner, activating the canonical NF-κB signaling pathway (characterized by IκB degradation and p65 nuclear translocation). This positive feedback loop significantly magnifies the production of pro-inflammatory cytokines such as IL-6 and IL-8, ultimately orchestrating massive neutrophil recruitment and driving the hyper-inflammation observed in severe pneumonia. Created in BioRender [You (2026) https://BioRender.com/qo9szis ].

Article Snippet: The concentrations of secreted S100A8/A9 heterodimer, IL-8, and IL-6 were quantified by commercial Quantikine ELISA kits (R&D Systems, Cat# DS8900 for S100A8/A9, D8000C for IL-8, and D6050B for IL-6).

Techniques: Amplification, Infection, Produced, Translocation Assay

Journal: Frontiers in Microbiology

Article Title: Klebsiella pneumoniae infection induces an S100A8/A9-mediated autocrine loop in human airway epithelium to amplify inflammation

doi: 10.3389/fmicb.2026.1768140

Figure Lengend Snippet: Klebsiella pneumoniae infection directly induces S100A8/A9 expression and secretion in HBE cells. Primary HBE cells were infected with WT K. pneumoniae or an isogenic acapsular mutant (Δ cps ). (A,B) Expression of S100A8 and S100A9 was determined by qRT-PCR at 8 h post-infection with various MOIs of K. pneumoniae , or 100 MOI K. pneumoniae for 4–12 h (C,D) . Data are normalized to the housekeeping gene GAPDH and expressed as fold change relative to uninfected control cells. (E) Secretion of S100A8/A9 heterodimer induced by WT K. pneumoniae and the isogenic Δ cps mutant at indicated MOIs after 24 h. All data are presented as mean ± SEM of three independent experiments. * p < 0.05, ** p < 0.01 vs. uninfected cells (A–D) . Statistical differences between the WT and Δ cps groups were determined by Two-way ANOVA followed by Tukey’s post-hoc test. * p < 0.05 compared between strains at the same MOI (E) .

Article Snippet: For S100A8/A9 stimulating experiment, cells were incubated with endotoxin-free recombinant human S100A8/A9 protein (R&D Systems) at the indicated concentrations for specified durations.

Techniques: Infection, Expressing, Mutagenesis, Quantitative RT-PCR, Control

Journal: Frontiers in Microbiology

Article Title: Klebsiella pneumoniae infection induces an S100A8/A9-mediated autocrine loop in human airway epithelium to amplify inflammation

doi: 10.3389/fmicb.2026.1768140

Figure Lengend Snippet: Extracellular S100A8/A9 functions as a potent pro-inflammatory stimulus for primary HBE cells. (A) Primary HBE cells were infected with WT K. pneumoniae (MOI 100) for the indicated time points. Relative mRNA expression of TLR4 was determined by qRT-PCR, with data calibrated to GAPDH and shown as fold induction over the baseline (0 h). (B) Representative western blot showing total TLR4 protein levels. β -Actin served as the housekeeping protein. (C) Quantification of TLR4 protein expression from three independent replicates, with values standardized to β-Actin. (D,E) HBE cells were treated for 24 h with the specified doses of endotoxin-free recombinant human S100A8/A9 (rS100A8/A9). The release of (D) IL-8 and (E) IL-6 was detected by ELISA. Data are presented as mean ± SEM of three independent experiments. * p < 0.05 versus the untreated control (A,C,D,E) .

Article Snippet: For S100A8/A9 stimulating experiment, cells were incubated with endotoxin-free recombinant human S100A8/A9 protein (R&D Systems) at the indicated concentrations for specified durations.

Techniques: Infection, Expressing, Quantitative RT-PCR, Western Blot, Recombinant, Enzyme-linked Immunosorbent Assay, Control

Journal: Frontiers in Microbiology

Article Title: Klebsiella pneumoniae infection induces an S100A8/A9-mediated autocrine loop in human airway epithelium to amplify inflammation

doi: 10.3389/fmicb.2026.1768140

Figure Lengend Snippet: Epithelial-derived S100A8/A9 is functionally required for the full inflammatory response to K. pneumoniae infection. Primary HBE cells were transfected with control siRNA (siCtrl) or S100A9 siRNA (siA9). (A) Knockdown efficiency was confirmed 48 h post-transfection by qRT-PCR analysis of S100A9 mRNA levels following a 12-h infection with WT K. pneumoniae (MOI 100), negative values represent fold reduction calculated as the negative inverse of 2 −ΔΔCt following the Schmittgen and Livak protocol. (B) Functional knockdown was confirmed by measuring S100A8/A9 protein secretion by ELISA in supernatants from infected cells at 24 h. (C,D) Control and S100A9 -deficient cells were infected with WT K. pneumoniae (MOI 100) for 24 h, and the secretion of cytokines were quantified by ELISA. Data are presented as mean ± SEM of three independent experiments. * p < 0.05 vs. Kp + siCtrl (A,B) or uninfected cells (C,D) , # p < 0.05 vs. Kp + siCtrl (C,D) .

Article Snippet: For S100A8/A9 stimulating experiment, cells were incubated with endotoxin-free recombinant human S100A8/A9 protein (R&D Systems) at the indicated concentrations for specified durations.

Techniques: Derivative Assay, Infection, Transfection, Control, Knockdown, Quantitative RT-PCR, Functional Assay, Enzyme-linked Immunosorbent Assay

Journal: Frontiers in Microbiology

Article Title: Klebsiella pneumoniae infection induces an S100A8/A9-mediated autocrine loop in human airway epithelium to amplify inflammation

doi: 10.3389/fmicb.2026.1768140

Figure Lengend Snippet: TLR4 is the essential receptor mediating S100A8/A9-induced inflammation in HBE cells during K. pneumoniae infection. (A,B) HBE cells were pre-incubated with neutralizing antibodies against TLR4 (10 μg/mL), RAGE (100 μg/mL), or an isotype control (Iso Ctrl) for 1 h, followed by stimulation with recombinant human S100A8/A9 (20 μg/mL) for 24 h. Levels of (A) IL-8 and (B) IL-6 in supernatants were determined by ELISA. (C,D) HBE cells were pre-treated with the indicated antibodies for 1 h and subsequently infected with WT K. pneumoniae (MOI 100) for 24 h. Secretion of (C) IL-8 and (D) IL-6 was quantified by ELISA. All results are expressed as mean ± SEM of three independent experiments. * p < 0.05 compared with the indicated groups.

Article Snippet: For S100A8/A9 stimulating experiment, cells were incubated with endotoxin-free recombinant human S100A8/A9 protein (R&D Systems) at the indicated concentrations for specified durations.

Techniques: Infection, Incubation, Control, Recombinant, Enzyme-linked Immunosorbent Assay

Journal: Frontiers in Microbiology

Article Title: Klebsiella pneumoniae infection induces an S100A8/A9-mediated autocrine loop in human airway epithelium to amplify inflammation

doi: 10.3389/fmicb.2026.1768140

Figure Lengend Snippet: The S100A8/A9 autocrine loop drives NF-κB activation and subsequent cytokine release in HBE cells. (A) Representative immunoblots showing degradation of IκBα in primary HBE cells stimulated with rS100A8/A9 (20 μg/mL) for 60 min. β-Actin served as a loading control. (B) Densitometric quantification of IκBα protein levels from (A) . (C) Representative immunofluorescence images showing subcellular localization of the p65 subunit (green) at 60 min post-stimulation with rS100A8/A9. Nuclei were counterstained with DAPI (blue). (D) HBE cells were transfected with control siRNA (siCtrl) or siRNA targeting S100A9 (siS100A9) and subsequently infected with wild-type K. pneumoniae (MOI 100). Representative immunoblots of IκBα levels are shown at 60 min post-infection. (E) Densitometric quantification of IκBα degradation from (D) . (F) Representative immunofluorescence images showing p65 localization (green) in siCtrl- or siS100A9-transfected HBE cells at 60 min post- K. pneumoniae infection. Nuclei were stained with DAPI (blue). (G) Secretion of IL-8 and IL-6 by HBE cells. Cells were pre-treated with or without the NF-κB inhibitor BAY 11–7,082 (10 μM) for 60 min, followed by stimulation with rS100A8/A9 (20 μg/mL) for 24 h. Cytokine levels in supernatants were measured by ELISA. All graphs display mean ± SEM, * p < 0.05 compared with the untreated control (B,E,G) ; # p < 0.05 compared with siCtrl + Kp or the S100A8/A9-stimulated group without inhibitor (E,G) .

Article Snippet: For S100A8/A9 stimulating experiment, cells were incubated with endotoxin-free recombinant human S100A8/A9 protein (R&D Systems) at the indicated concentrations for specified durations.

Techniques: Activation Assay, Western Blot, Control, Immunofluorescence, Transfection, Infection, Staining, Enzyme-linked Immunosorbent Assay

Journal: Frontiers in Microbiology

Article Title: Klebsiella pneumoniae infection induces an S100A8/A9-mediated autocrine loop in human airway epithelium to amplify inflammation

doi: 10.3389/fmicb.2026.1768140

Figure Lengend Snippet: The epithelial S100A8/A9 autocrine loop is a critical driver of neutrophil chemotaxis in response to K. pneumoniae infection. Neutrophil chemotaxis was assessed using a Transwell assay. (A) Comparison of the chemotactic activity of supernatants from uninfected HBE cells (conditioned medium, CM), HBE cells infected with WT K. pneumoniae (MOI 100), and fMLP (positive control) on primary human neutrophils. (B) Comparison of the chemotactic activity of supernatants from infected control (siCtrl) HBE cells versus infected S100A9-deficient (siS100A9) HBE cells. Flow cytometry was used to determine the absolute number of migrated neutrophils. Data are shown as mean ± SEM from three separate experiments. * p < 0.05 vs. uninfected CM, # p < 0.05 vs. Kp + siCtrl.

Article Snippet: For S100A8/A9 stimulating experiment, cells were incubated with endotoxin-free recombinant human S100A8/A9 protein (R&D Systems) at the indicated concentrations for specified durations.

Techniques: Chemotaxis Assay, Infection, Transwell Assay, Comparison, Activity Assay, Positive Control, Control, Flow Cytometry

Journal: Frontiers in Microbiology

Article Title: Klebsiella pneumoniae infection induces an S100A8/A9-mediated autocrine loop in human airway epithelium to amplify inflammation

doi: 10.3389/fmicb.2026.1768140

Figure Lengend Snippet: Proposed model of the S100A8/A9-mediated autocrine amplification loop in human airway epithelial cells during K. pneumoniae infection. Initial recognition of encapsulated K. pneumoniae by the airway epithelium triggers a primary transcriptional response, leading to the synthesis and secretion of the alarmin S100A8/A9 and a simultaneous upregulation of its cognate receptor, TLR4. This dual mechanism creates a primed state within the epithelium. The endogenously produced S100A8/A9 then acts back on the enriched TLR4 receptors in an autocrine or paracrine manner, activating the canonical NF-κB signaling pathway (characterized by IκB degradation and p65 nuclear translocation). This positive feedback loop significantly magnifies the production of pro-inflammatory cytokines such as IL-6 and IL-8, ultimately orchestrating massive neutrophil recruitment and driving the hyper-inflammation observed in severe pneumonia. Created in BioRender [You (2026) https://BioRender.com/qo9szis ].

Article Snippet: For S100A8/A9 stimulating experiment, cells were incubated with endotoxin-free recombinant human S100A8/A9 protein (R&D Systems) at the indicated concentrations for specified durations.

Techniques: Amplification, Infection, Produced, Translocation Assay

Journal: Frontiers in Microbiology

Article Title: Klebsiella pneumoniae infection induces an S100A8/A9-mediated autocrine loop in human airway epithelium to amplify inflammation

doi: 10.3389/fmicb.2026.1768140

Figure Lengend Snippet: Extracellular S100A8/A9 functions as a potent pro-inflammatory stimulus for primary HBE cells. (A) Primary HBE cells were infected with WT K. pneumoniae (MOI 100) for the indicated time points. Relative mRNA expression of TLR4 was determined by qRT-PCR, with data calibrated to GAPDH and shown as fold induction over the baseline (0 h). (B) Representative western blot showing total TLR4 protein levels. β -Actin served as the housekeeping protein. (C) Quantification of TLR4 protein expression from three independent replicates, with values standardized to β-Actin. (D,E) HBE cells were treated for 24 h with the specified doses of endotoxin-free recombinant human S100A8/A9 (rS100A8/A9). The release of (D) IL-8 and (E) IL-6 was detected by ELISA. Data are presented as mean ± SEM of three independent experiments. * p < 0.05 versus the untreated control (A,C,D,E) .

Article Snippet: The concentrations of secreted S100A8/A9 heterodimer, IL-8, and IL-6 were quantified by commercial Quantikine ELISA kits (R&D Systems, Cat# DS8900 for S100A8/A9, D8000C for IL-8, and D6050B for IL-6).

Techniques: Infection, Expressing, Quantitative RT-PCR, Western Blot, Recombinant, Enzyme-linked Immunosorbent Assay, Control

Journal: Frontiers in Microbiology

Article Title: Klebsiella pneumoniae infection induces an S100A8/A9-mediated autocrine loop in human airway epithelium to amplify inflammation

doi: 10.3389/fmicb.2026.1768140

Figure Lengend Snippet: Epithelial-derived S100A8/A9 is functionally required for the full inflammatory response to K. pneumoniae infection. Primary HBE cells were transfected with control siRNA (siCtrl) or S100A9 siRNA (siA9). (A) Knockdown efficiency was confirmed 48 h post-transfection by qRT-PCR analysis of S100A9 mRNA levels following a 12-h infection with WT K. pneumoniae (MOI 100), negative values represent fold reduction calculated as the negative inverse of 2 −ΔΔCt following the Schmittgen and Livak protocol. (B) Functional knockdown was confirmed by measuring S100A8/A9 protein secretion by ELISA in supernatants from infected cells at 24 h. (C,D) Control and S100A9 -deficient cells were infected with WT K. pneumoniae (MOI 100) for 24 h, and the secretion of cytokines were quantified by ELISA. Data are presented as mean ± SEM of three independent experiments. * p < 0.05 vs. Kp + siCtrl (A,B) or uninfected cells (C,D) , # p < 0.05 vs. Kp + siCtrl (C,D) .

Article Snippet: The concentrations of secreted S100A8/A9 heterodimer, IL-8, and IL-6 were quantified by commercial Quantikine ELISA kits (R&D Systems, Cat# DS8900 for S100A8/A9, D8000C for IL-8, and D6050B for IL-6).

Techniques: Derivative Assay, Infection, Transfection, Control, Knockdown, Quantitative RT-PCR, Functional Assay, Enzyme-linked Immunosorbent Assay

Journal: Frontiers in Microbiology

Article Title: Klebsiella pneumoniae infection induces an S100A8/A9-mediated autocrine loop in human airway epithelium to amplify inflammation

doi: 10.3389/fmicb.2026.1768140

Figure Lengend Snippet: TLR4 is the essential receptor mediating S100A8/A9-induced inflammation in HBE cells during K. pneumoniae infection. (A,B) HBE cells were pre-incubated with neutralizing antibodies against TLR4 (10 μg/mL), RAGE (100 μg/mL), or an isotype control (Iso Ctrl) for 1 h, followed by stimulation with recombinant human S100A8/A9 (20 μg/mL) for 24 h. Levels of (A) IL-8 and (B) IL-6 in supernatants were determined by ELISA. (C,D) HBE cells were pre-treated with the indicated antibodies for 1 h and subsequently infected with WT K. pneumoniae (MOI 100) for 24 h. Secretion of (C) IL-8 and (D) IL-6 was quantified by ELISA. All results are expressed as mean ± SEM of three independent experiments. * p < 0.05 compared with the indicated groups.

Article Snippet: The concentrations of secreted S100A8/A9 heterodimer, IL-8, and IL-6 were quantified by commercial Quantikine ELISA kits (R&D Systems, Cat# DS8900 for S100A8/A9, D8000C for IL-8, and D6050B for IL-6).

Techniques: Infection, Incubation, Control, Recombinant, Enzyme-linked Immunosorbent Assay

Journal: Frontiers in Microbiology

Article Title: Klebsiella pneumoniae infection induces an S100A8/A9-mediated autocrine loop in human airway epithelium to amplify inflammation

doi: 10.3389/fmicb.2026.1768140

Figure Lengend Snippet: The S100A8/A9 autocrine loop drives NF-κB activation and subsequent cytokine release in HBE cells. (A) Representative immunoblots showing degradation of IκBα in primary HBE cells stimulated with rS100A8/A9 (20 μg/mL) for 60 min. β-Actin served as a loading control. (B) Densitometric quantification of IκBα protein levels from (A) . (C) Representative immunofluorescence images showing subcellular localization of the p65 subunit (green) at 60 min post-stimulation with rS100A8/A9. Nuclei were counterstained with DAPI (blue). (D) HBE cells were transfected with control siRNA (siCtrl) or siRNA targeting S100A9 (siS100A9) and subsequently infected with wild-type K. pneumoniae (MOI 100). Representative immunoblots of IκBα levels are shown at 60 min post-infection. (E) Densitometric quantification of IκBα degradation from (D) . (F) Representative immunofluorescence images showing p65 localization (green) in siCtrl- or siS100A9-transfected HBE cells at 60 min post- K. pneumoniae infection. Nuclei were stained with DAPI (blue). (G) Secretion of IL-8 and IL-6 by HBE cells. Cells were pre-treated with or without the NF-κB inhibitor BAY 11–7,082 (10 μM) for 60 min, followed by stimulation with rS100A8/A9 (20 μg/mL) for 24 h. Cytokine levels in supernatants were measured by ELISA. All graphs display mean ± SEM, * p < 0.05 compared with the untreated control (B,E,G) ; # p < 0.05 compared with siCtrl + Kp or the S100A8/A9-stimulated group without inhibitor (E,G) .

Article Snippet: The concentrations of secreted S100A8/A9 heterodimer, IL-8, and IL-6 were quantified by commercial Quantikine ELISA kits (R&D Systems, Cat# DS8900 for S100A8/A9, D8000C for IL-8, and D6050B for IL-6).

Techniques: Activation Assay, Western Blot, Control, Immunofluorescence, Transfection, Infection, Staining, Enzyme-linked Immunosorbent Assay