Basophils are evolutionarily conserved in vertebrates, despite their small numbers and short life span, suggesting that they have beneficial roles in maintaining health. However, these roles are not fully defined. Here we demonstrate that basophil-deficient mice exhibit reduced bacterial clearance and increased morbidity and mortality in the cecal ligation and puncture (CLP) model of sepsis. Among the several proinflammatory mediators that we measured, tumor necrosis factor (TNF) was the only cytokine that was significantly reduced in basophil-deficient mice after CLP. In accordance with that observation, we found that mice with genetic ablation of Tnf in basophils exhibited reduced systemic concentrations of TNF during endotoxemia. Moreover, after CLP, mice whose basophils could not produce TNF, exhibited reduced neutrophil and macrophage TNF production and effector functions, reduced bacterial clearance, and increased mortality. Taken together, our results show that basophils can enhance the innate immune response to bacterial infection and help prevent sepsis.
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The authors declare that the main data supporting the findings of this study are available within the article and its supplementary figures. Additional data are available from the corresponding authors upon request.
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The authors thank R.M. Locksley for providing the Basoph8 mice and members of the Piliponsky and Galli laboratories for helpful discussions. Research in the Piliponsky laboratory was supported by National Institutes of Health (NIH) grant nos. R01 HL113351 and R01 HL141094, and an American Heart Association grant no. 12GRNT9680021. Research in the Galli laboratory was supported by NIH grant nos. R01 CA72074, R37 AI23990, R01 AI070813, and R01 AR067145, and by the Department of Pathology, Stanford University. Research in the Nedospasov laboratory was supported by a grant from the Russian Science Foundation (grant no. 14-50-00060).
Integrated supplementary information
Supplementary Figure 1 Gating strategy to identify basophils among total peritoneal cells after CLP.
(a-i) Representative flow cytometry plots and frequencies used to identify basophils amongst peritoneal cells obtained from mice 24 h after induction of moderate CLP (50% ligation, one puncture with a 22G needle). (a) Cell population considered for analysis using FSC and SSC. (b) Doublets were removed using FSC-A and FSC-W gating. (c) Dead cells were removed from the analysis using DAPI dead cell stain. (d, e) FcεRIα+ c-Kit- (d) and CD49b+ (e) cells were gated and defined as basophils. (f, g) The same gating strategy was used to identify basophils amongst peritoneal cells obtained from CLP-treated basophil-deficient mice, which shows a significant reduction in the basophil percentage. (h, i) Peritoneal mast cells from naïve mice were used to establish gates for FcεRIα+ and c-Kit- cells. Data are representative of those obtained in the 3 independent experiments performed.
Supplementary Figure 2 Peritoneal neutrophils and macrophages from naïve mice express low levels of Mcpt8 mRNA.
Mcpt8 mRNA expression relative to GAPDH in Gr-1+ CD11b+ neutrophils (Neu) and F4/80+ CD11b+ macrophages (Macs) that were sorted from the peritoneum of naïve Tnffl/fl mice and Basoph8 x Tnffl/fl mice (n = 3 mice/group). Mcpt8 gene expression was assessed by qPCR using FcεRIα+ CD49b+ c-Kit– basophils that were sorted from bone marrow of Tnffl/fl mice as positive controls. Mcpt8 mRNA expression levels in neutrophils and macrophages were normalized against Mcpt8 mRNA expression levels found in bone marrow basophils (Bas). Data are shown as means + SEM with squares representing values for individual experiments. The qPCR data are representative of n = 3 independent experiments performed, each of which gave similar results.
(a-b) Compared with the Tnf+/+ mice, Tnf-/- mice exhibited increased peritoneal cavity (a) and blood (b) colony forming units (CFU) at 24 h after CLP. Data in a and b are shown as means with circles representing values from individual mice (n = 14 and n = 11 for Tnf+/+ mice in a and b, respectively, and n = 7 and n = 6 for Tnf-/- mice in a and b, respectively). P values by Mann-Whitney test.
(a-d) Percentages of leukocytes (a) Basophil percentages (FcεRIα+ CD49b+ c-Kit–) in the live-cell population isolated from spleens (Tnffl/fl, n = 7; Basoph8 x Tnffl/fl, n = 9), bone marrow (Tnffl/fl, n = 4; Basoph8 x Tnffl/fl, n = 9), or blood (Tnffl/fl, n = 16; Basoph8 x Tnffl/fl, n = 8), as analyzed by flow cytometry. (b) Neutrophil percentages (Gr-1+ CD11b+) in the live-cell population isolated from spleen (Tnffl/fl, n = 6; Basoph8 x Tnffl/fl, n = 6), bone marrow (Tnffl/fl, n = 6; Basoph8 x Tnffl/fl, n = 7), or peritoneal fluids (Tnffl/fl, n = 7; Basoph8 x Tnffl/fl, n = 10), as analyzed by flow cytometry. (c) Macrophage percentages (F4/80+ CD11b+) in the live-cell population isolated from spleens (Tnffl/fl, n = 7; Basoph8 x Tnffl/fl, n = 10) or peritoneal fluids (Tnffl/fl, n = 3; Basoph8 x Tnffl/fl, n = 10), as analyzed by flow cytometry. Data in a-d are depicted as mean + SEM with circles representing values for individual mice. (d) Mast cell percentages (FcεRIα+ c-Kit+) in the live-cell population isolated from peritoneal fluids (Tnffl/fl, n = 4; Basoph8 x Tnffl/fl, n = 6), as analyzed by flow cytometry. (e-g) Absolute numbers of leukocytes. (e) Blood monocyte (Tnffl/fl, n = 13; Basoph8 x Tnffl/fl, n = 9) and eosinophil (Tnffl/fl, n = 9; Basoph8 x Tnffl/fl, n = 10) numbers. (f) Blood lymphocyte (Tnffl/fl, n = 20; Basoph8 x Tnffl/fl, n = 10) and neutrophil (Tnffl/fl, n = 21; Basoph8 x Tnffl/fl, n = 9) numbers. (g) Blood lymphocyte (Tnffl/fl, n = 9; Basoph8 x Tnffl/fl, n = 9) and neutrophil (Tnffl/fl, n = 10; Basoph8 x Tnffl/fl, n = 8) numbers at 24 h after moderate CLP. Data in e-g are depicted as mean + SEM with circles representing values for individual mice. P values by Mann-Whitney test.
Supplementary Figure 5 Basophil-derived TNF contributes to increased TNF production by peritoneal macrophages during LPS-induced endotoxemia.
Representative flow cytometry plots for TNF positive cells in the macrophage populations obtained from the peritoneal cavity of Tnffl/fl and Basoph8 x Tnffl/fl mice (n = 4/group) 1 h after i.p. injection of LPS (10 μg). Cells were immunostained for TNF in addition to surface F4/80 and CD11b to identify macrophages. Data were obtained from two independent experiments performed, each of which gave similar results.
Supplementary Figure 6 Disruption of Mcpt8 expression levels in Basoph8 mice does not impact the outcome of CLP of moderate severity.
(a, b) Mcpt8 expression levels are significantly reduced or undetectable in basophils from mice with one or two Basoph8 gene copies, respectively. Mcpt8 mRNA (a) and protein (b) expression levels in basophils that were sorted from bone marrow cells harvested from naïve mice (a) or from FcεRIα+ CD49b+ c-Kit– bone marrow-derived cells cultured in the presence of IL-3 (b). The qPCR data in a and western blot analysis in b are representative of 2 independent experiments performed, each of which gave similar results. The Western blot analysis in b was cropped from the original blot shown in Supplementary Fig. 7. (c, d) Basophil-derived TNF-deficient mice with one Basoph8 gene copy (mice with a significant reduction in Mcpt8 expression levels) exhibit similar mortality and morbidity as basophil-derived TNF-deficient mice with two Basoph8 gene copies (mice with a total Mcpt8 deficiency). Survival after moderate CLP in littermate control mice (Tnffl/fl = Basoph8 -/- x Tnffl/fl, n = 15), Basoph8+/- x Tnffl/fl (n = 7) and Basoph8+/+ x Tnffl/fl (n = 7). *P < 0.05 and **P < 0.01 vs. Tnffl/fl mice. P values by Logrank (Mantel-Cox test). (d) Drop in body temperature in Tnffl/fl mice (n = 7), Basoph8± x Tnffl/fl mice (n = 13) and Basoph8+/+ x Tnffl/fl mice (n = 17) at 24 h after CLP. P values by Mann-Whitney test. Data in c were pooled from the n = 3 independent experiments performed, each of which gave similar results. Data in d are shown as means + SEM with circles representing values for individual mice and were pooled from n = 3 independent experiments performed, each of which gave similar results. (e-j) Mice with one Basoph8 gene copy (that is, Basoph8± x Tnf +/+ mice with no Mcpt8 protein expression, but which express basophil-derived TNF) exhibit morbidity rates similar to their littermate controls [Tnf +/+ mice]). (e-j) Drop in body temperature (e), colony forming units (CFU) in peritoneal cavity (f) and blood (g), amount of intraperitoneal TNF (h), and numbers of neutrophils (i) and macrophages (j) in the peritoneal live-cell population analyzed by flow cytometry (Gr-1+ CD11b+ cells for neutrophils and F4/80+ CD11b+ for macrophages) in Basoph8-/- x Tnf+/+ mice and Basoph8± x Tnf+/+ mice at 24 h after CLP. Data are shown as means + SEM with circles representing values for individual mice (n = 23 in e, n = 19 in f, n = 16 in g, n = 14 in h and n = 7 in i and j for Basoph8-/- x Tnf+/+ mice; and n = 9 in e, n = 14 in f, n = 13 in g, n = 7 in h and n = 5 in i and j for Basoph8± x Tnf+/+ mice. Data were pooled from n = 3 independent experiments performed, each of which gave similar results.
Blots show Mcpt8 (a) and GAPDH (b) expression levels in basophils from mice with one or two Basoph8 gene copies, respectively. Mcpt8 and GAPDH protein expression levels in increasing number of basophils that were sorted from FcεRIα+ CD49b+ c-Kit– bone marrow-derived cells cultured in the presence of IL-3. Blots are representative of 2 independent experiments performed, each of which gave similar results.
Supplementary Figure 8 Neutrophils, macrophages and mast cells from Basoph8 × Tnffl/fl mice express negligible YFP and Mcpt8 mRNA after CLP.
(a) Representative flow cytometry plots and cell frequencies in the peritoneal neutrophil, macrophage, mast cell and basophil populations obtained from Tnffl/fl mice (n = 3) and Basoph8± x Tnffl/fl mice (n = 3) at 24 h after moderate CLP. Cells were immunostained for surface Gr-1 and CD11b for peritoneal neutrophils; with F4/80 and CD11b for macrophages; and with FcεRIα, c-Kit and CD49b for mast cells (FcεRIα+ c-Kit+) and basophils (FcεRIα+ CD49b+). (b) The specificity of Mcpt8 gene expression as assessed by single cell PCR detection in peritoneal neutrophils (Neu), macrophages (Macs), mast cells (MCs), and BM basophils (BMBas) obtained from Tnffl/fl mice and Basoph8± x Tnffl/fl mice at 24 h after moderate CLP. The numbers above the bar graphs indicate the number of cells analyzed. Results are expressed as % of cells expressing transcripts for the PCR products analyzed/cell type; results were pooled from n = 3 sorting experiments.
Supplementary Figure 9 TNF ablation in basophils does not affect ROS production and phagocytosis in neutrophils and macrophages ex vivo.
Neutrophil ROS production (a) and macrophage phagocytosis (b). Bone marrow neutrophils were loaded for 30 min at 37 °C with 1 μM of CM-H2DCFDA, which is a general oxidative stress indicator, and then activated with 100 ng/ml of PMA. Peritoneal macrophages were incubated with opsonized FITC-labeled E. coli (K-12 strain) bioparticles for 10 min at 37 °C. Cells were stained for neutrophil and macrophage-specific surface markers and flow cytometry analysis was performed immediately thereafter. Data in a and b are shown as means + SEM with squares showing values for individual mice (n = 4 for Tnffl/fl mice in a and b, and n = 3 and n = 4 for Basoph8 x Tnffl/fl mice in a and b, respectively). Data were pooled from n = 2 independent experiments.
Flow cytometry plots and frequencies (a) and mean fluorescence intensities (b) for IL-6 positive cells in the peritoneal neutrophil and macrophage populations obtained from Tnffl/fl mice and Basoph8 x Tnffl/fl mice (n = 6 mice/group) at 24 h after CLP and then incubated ex vivo for 4 h in the presence of GolgiPlug. Cells were immunostained for IL-6 in addition to surface Gr-1 and CD11b to identify peritoneal neutrophils or surface F4/80 and CD11b to identify macrophages. Data in a are from one representative experiment of the n = 2 independent experiments performed, each of which gave similar results. The data in b were pooled from n = 2 independent experiments that were performed. Data are shown as means + SEM with squares showing values for cells obtained from individual mice (n = 6/group). P values by Mann-Whitney test.
Supplementary Figs. 1–10 and Supplementary Table 1. Association between FCER1A expression in whole blood and clinical attributes in trauma patients at 7 d after severe injury. The dataset was obtained from 167 severely injured patients and compared with 35 healthy individuals (ages 16–55) (http://web.mgh.harvard.edu/TRT/).