Divergent roles of IL-23 and IL-12 in host defense against Klebsiella pneumoniae - PubMed (original) (raw)

Divergent roles of IL-23 and IL-12 in host defense against Klebsiella pneumoniae

Kyle I Happel et al. J Exp Med. 2005.

Abstract

Interleukin (IL)-23 is a heterodimeric cytokine that shares the identical p40 subunit as IL-12 but exhibits a unique p19 subunit similar to IL-12 p35. IL-12/23 p40, interferon gamma (IFN-gamma), and IL-17 are critical for host defense against Klebsiella pneumoniae. In vitro, K. pneumoniae-pulsed dendritic cell culture supernatants elicit T cell IL-17 production in a IL-23-dependent manner. However, the importance of IL-23 during in vivo pulmonary challenge is unknown. We show that IL-12/23 p40-deficient mice are exquisitely sensitive to intrapulmonary K. pneumoniae inoculation and that IL-23 p19-/-, IL-17R-/-, and IL-12 p35-/- mice also show increased susceptibility to infection. p40-/- mice fail to generate pulmonary IFN-gamma, IL-17, or IL-17F responses to infection, whereas p35-/- mice show normal IL-17 and IL-17F induction but reduced IFN-gamma. Lung IL-17 and IL-17F production in p19-/- mice was dramatically reduced, and this strain showed substantial mortality from a sublethal dose of bacteria (10(3) CFU), despite normal IFN-gamma induction. Administration of IL-17 restored bacterial control in p19-/- mice and to a lesser degree in p40-/- mice, suggesting an additional host defense requirement for IFN-gamma in this strain. Together, these data demonstrate independent requirements for IL-12 and IL-23 in pulmonary host defense against K. pneumoniae, the former of which is required for IFN-gamma expression and the latter of which is required for IL-17 production.

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Figures

Figure 1.

Figure 1.

Animals with targeted gene deletion in the IL-12, IL-17, and IL-23 signaling pathways demonstrate increased mortality during intrapulmonary K. pneumoniae infection. (A) WT C57BL/6, IL-23 p19−/−, IL-12 p35−/−, IL-12 p40−/−, or IL-17R−/− mice were challenged with 104 CFU intratracheal K. pneumoniae and survival was recorded every 12 h (n = 16–20 per group). IL-12 p40 knockout mice showed the greatest susceptibility to infection (*P < 0.01 compared with C57BL/6 [log rank test]). Survival differences between IL-23 p19−/−, IL-17R−/−, and IL-12 p35−/− mice were not statistically significant. (B) WT and p19−/− mice were also challenged with a lower dose (103 CFU) of bacteria, demonstrating significant mortality in p19−/− mice to a sublethal dose of K. pnuemoniae (*P < 0.01 compared with WT mice; n = 10 per group).

Figure 2.

Figure 2.

Cytokine mRNA expression following pulmonary K. pneumoniae infection. Animals were administered 104 CFU bacteria and killed at specified time points. BAL cell pellet and lung homogenate mRNA were assayed via real-time RT-PCR. (A) Increases in BAL cell IL-23 p19, IL-12/23 p40, and IL-12 p35 mRNA expression during infection (n = 4–5 per group). (B) Whole lung tissue IL-23 p19, IL-17, and IL-17F mRNA expression following infection (n = 4–5 per group). Data are normalized for 18s ribosomal RNA content and plotted as fold change over baseline (time 0) expression. *Earliest significant (P < 0.05) increase in expression compared with time zero transcripts. Error bars represent mean ± SD.

Figure 3.

Figure 3.

AM IL-23 expression is required for induction of splenocyte IL-17 expression in response to K. pneumoniae. (A) AMs from naive WT, p35−/−, p40−/−, and p19−/− mice were recovered via BAL and exposed in vitro to K. pneumoniae. After 24 h, supernatants were harvested, centrifuged, and placed onto adherent cell-depleted WT splenocytes for 24 h to assay IL-17 induction (n = 5 per group; *P < 0.05 compared with media control). (B) IL-23 p19 mRNA expression in unexposed mDCs (mDC-control) or pDCs (pDC-control) or mDCs, AMs, and pDCs following 2-h in vitro exposure to K. pneumoniae. Data are expressed as fold increase in p19 expression compared with mDC- or pDC-control (n = 4–5 per group; *P < 0.05 compared with mDC-control). Error bars represent mean ± SD.

Figure 4.

Figure 4.

IL-23 expression is required for lung IL-17 and IL-17F expression, whereas IL-12 is necessary for IFN-γ induction in response to K. pneumoniae infection. WT, p35−/−, p40−/−, and p19−/− mice were infected with 104 CFU K. pneumoniae and killed 24 h after infection. (A, B) Whole lung homogenate IL-17 (A) and IL-17F (B) mRNA expression as measured via real-time RT-PCR. (C) Whole lung homogenate IL-17 protein expression in repeat experiments. (D) Lung homogenate IFN-γ content in response to infection, indicating IL-23 is not sufficient to induce IFN-γ in the absence of IL-12. (E) Lung homogenate IFN-γ mRNA 24 h after K. pneumoniae infection confirms equivalent IFN-γ expression in WT and IL-23 p19−/− mice (n = 6 per group; *P < 0.05 compared with WT). Error bars represent mean ± SD.

Figure 5.

Figure 5.

IL-23 p19−/− mice have reduced cytokine and chemokine responses to K. pneumoniae infection. Whole lung cytokine and chemokine content were measured in lung homogenates 24 h after 104 CFU K. pneumoniae delivery. Values are normalized to homogenate protein concentration (n = 6 per group; *P < 0.05 compared with WT). Error bars represent mean ± SD.

Figure 6.

Figure 6.

Defects in pulmonary host defense in IL-23 p19−/− mice are rescued by IL-17 treatment. WT C57BL/6 or IL-23 p19−/− mice were challenged with 104 K. pneumoniae followed by intratracheal administration of 1.5 μg recombinant murine IL-17 (or phosphate-buffered saline vehicle) 12 h later. Animals were then killed 24 h after rmIL-17 (or vehicle) delivery. (A) IL-17 improves bacterial clearance in IL-23 p19−/− mice. (B) IL-17 restores pulmonary concentrations of G-CSF, KC, and LIX in IL-23 p19−/− mice. (C) IL-17 partially improves bacterial clearance in IL-12 p40−/− mice. *P < 0.05 compared with WT vehicle-treated control. **P < 0.05 compared with vehicle-treated group of same genotype (n = 4–6 per group). Error bars represent mean ± SD.

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