Interleukin 17 Receptor E (IL-17RE) and IL-17C Mediate the Recruitment of Neutrophils during Acute Streptococcus pneumoniae Pneumonia

Abstract

Neutrophils contribute to lung injury in acute pneumococcal pneumonia. The interleukin 17 receptor E (IL-17RE) is the functional receptor for the epithelial-derived cytokine IL-17C, which is known to mediate innate immune functions. The aim of this study was to investigate the contribution of IL-17RE/IL-17C to pulmonary inflammation in a mouse model of acute Streptococcus pneumoniae pneumonia. Numbers of neutrophils and the expression levels of the cytokine granulocyte colony-stimulating factor (G-CSF) and tumor necrosis factor alpha (TNF-α) were decreased in lungs of IL-17RE-deficient (Il-17re^-/- ) mice infected with S. pneumoniae Numbers of alveolar macrophages rapidly declined in both wild-type (WT) and Il-17re^-/- mice and recovered 72 h after infection. There were no clear differences in the elimination of bacteria and numbers of blood granulocytes between infected WT and Il-17re^-/- mice. The fractions of granulocyte-monocyte progenitors (GMPs) were significantly reduced in infected Il-17re^-/- mice. Numbers of neutrophils were significantly reduced in lungs of mice deficient for IL-17C 24 h after infection with S. pneumoniae These data indicate that the IL-17C/IL-17RE axis promotes the recruitment of neutrophils without affecting the recovery of alveolar macrophages in the acute phase of S. pneumoniae lung infection.

Keywords: G-CSF; IL-17; IL-17C; IL-17RE; Streptococcus pneumoniae; host defense; lung infection; neutrophils; pneumonia; sepsis.

FIG 1

Deficiency for Il-17RE results in decreased recruitment of neutrophils during acute S. pneumoniae pneumonia. WT and Il-17re^−/− mice were intranasally infected with S. pneumoniae (∼5 × 10⁶ CFU per mouse) or treated with PBS as a control. Numbers of viable bacteria (CFU) were determined in BAL fluids (A) at the indicated time points (hours). Numbers of total cells (B), neutrophils (C), macrophages (D), and lymphocytes (E) were determined in cytospin preparations. Data are shown as the means ± standard deviations (n = 11 and 9 for sham-infected mice, n = 8 and 5 for 4-h-infected mice, n = 9 and 5 for 24-h-infected mice, n = 10 and 8 for 72-h-infected mice). Significant differences in results for infected mice compared to those for the corresponding sham-infected mice are indicated as follows: +, P < 0.05; ++, P < 0.01; +++, P < 0.001. Significant differences in results for infected Il-17re^−/− mice compared to those for the corresponding infected WT mice are indicated as follows: *, P < 0.05; ***, P < 0.001. (F to I) Representative lung histology (hematoxylin and eosin staining [H&E]), inflammatory score (n = 10 and 8 mice per group), representative immunohistochemistry of TNF-α, and quantification of TNF-α-positive cells in lung parenchyma (n = 5 and 6 mice per group) of mice infected with S. pneumoniae for 24 h (scale bar, 200 μm) were determined. Data are shown as the means ± standard deviations. ***, P < 0.001. HP, high-power field.

FIG 2

IL-17RE promotes the expression of G-CSF during acute S. pneumoniae pneumonia. WT and Il-17re^−/− mice were intranasally infected with S. pneumoniae (∼5 × 10⁶ CFU per mouse) or treated with PBS as a control. Concentrations of G-CSF (A), KC (B), and MIP-2 (C) were measured in BAL fluids by ELISA at indicated time points (hours). Data are shown as the means ± standard deviations (n = 9 and 8 for sham-infected mice, n = 8 and 5 for 4-h-infected mice, n = 5 and 4 for 24-h-infected mice). Significant differences in results for infected mice compared to those for the corresponding sham-infected mice are indicated as follows: +, P < 0.05; ++, P < 0.01; +++, P < 0.001. *, P < 0.05 for the difference between results for infected Il-17re^−/− mice and those for infected WT mice (*). (D) The expression levels of IL-17A, IL-17C, IL-17D, and IL-17RE in lung tissue of WT mice were measured by qRT-PCR at 4 h postinfection. Data are shown as the means ± standard deviations (n = 6 for sham-infected mice, n = 9 for 4-h infected mice). Significant differences in results for infected WT mice compared to those for sham-infected mice are indicated as follows: +, P < 0.05; ++, P < 0.01; +++, P < 0.001.

FIG 3

Evaluation of leukocytes and differentiation of hematopoietic cells during acute S. pneumoniae pneumonia. WT and Il-17re^−/− mice were intranasally infected with S. pneumoniae (∼5 × 10⁶ CFU per mouse) or treated with PBS as a control. (A) Leukocytes were differentiated by light microscopy. (B to E) Differentiation of hematopoietic cells was analyzed by flow cytometry analysis. Data are shown as the means ± standard deviations (n = 4 to 6 per group). +, P < 0.05; ++, P < 0.01, for a comparison of results in infected mice to those of corresponding sham-infected mice.

FIG 4

IL-17C promotes the recruitment of neutrophils during acute S. pneumoniae pneumonia. WT and Il-17c^−/− mice were intranasally infected with S. pneumoniae (∼8 × 10⁶ CFU per mouse). Numbers of viable bacteria (CFU) were determined in BAL fluids (A). Numbers of total cells (B), neutrophils (C), macrophages (D), and lymphocytes (E) were determined in cytospin preparations. Data are shown as the means ± standard deviations (n = 6 per group). **, P < 0.01, for a comparison of results in infected Il-17re^−/− mice to those in infected WT mice.