Lab Anim Res.  2018 Dec;34(4):295-301. 10.5625/lar.2018.34.4.295.

Nucleotide-binding oligomerization domain 1 is dispensable for host immune responses against pulmonary infection of Acinetobacter baumannii in mice

• Kang MJ
• Choi JA
• Choi JH
• Jang AR
• Park JY
• Ahn JH
• Lee TS
• Kim DY
• Park JH

• KMID: 2459308
• DOI: http://doi.org/10.5625/lar.2018.34.4.295

Abstract

Nucleotide-binding domain 1 (Nod1) is a cytosolic receptor that is responsible for the recognition of a bacterial peptidoglycan motif containing meso-diaminophimelic acid. In this study, we sought to identify the role of Nod1 in host defense in vivo against pulmonary infection by multidrug resistant Acinetobacter baumannii. Wildtype (WT) and Nod1-deficient mice were intranasally infected with 3×107 CFU of A. baumannii and sacrificed at 1 and 3 days post-infection (dpi). Bacterial CFUs, cytokines production, histopathology, and mouse β-defensins (mBD) in the lungs of infected mice were evaluated. The production of cytokines in response to A. baumannii was also measured in WT and Nod1-deficient macrophages. The bacterial clearance in the lungs was not affected by Nod1 deficiency. Levels of IL-6, TNF-α, and IL-1β in the lung homogenates were comparable at days 1 and 3 between WT and Nod1-deficient mice, except the TNF-α level at day 3, which was higher in Nod1-deficient mice. There was no significant difference in lung pathology and expression of mBDs (mBD1, 2, 3, and 4) between WT and Nod1-deficient mice infected with A. baumannii. The production of IL-6, TNF-α, and NO by macrophages in response to A. baumannii was also comparable in WT and Nod1-deficient mice. Our results indicated that Nod1 does not play an important role in host immune responses against A. baumannii infection.

Keyword

Nucleotide-binding domain 1 (Nod1); peptidoglycan; Acinetobacter baumannii

MeSH Terms

Acinetobacter baumannii*
Acinetobacter*
Animals
Cytokines
Cytosol
Interleukin-6
Lung
Macrophages
Mice*
Pathology
Peptidoglycan
Cytokines
Interleukin-6
Peptidoglycan

Figure

• 

  Figure 1 Nod1 does not affect bacterial clearance in the lungs of A. baumannii-infected mice. WT and Nod1-deficient mice (n=5–6 mice per group) were intranasally (i.n) infected with A. baumannii (3×107 CFU) and sacrificed at 1 and 3 days after infection. Bacterial loads in lung homogenates were counted by agar plating assay. This experiment was repeated twice independently, and the results are provided separately (A and B).

• 

  Figure 2 Cytokines production in the lung homogenates of WT and Nod1-deficient mice infected with A. baumannii. WT and Nod1-deficient mice (n=5–6 mice per group) were i.n infected with A. baumannii (3×107 CFU). Lung homogenates were collected at 1 and 3 days after infection. Levels of IL-6, TNF-α, and IL-1β were measured by ELISA (A–C). Results are from one of two independent experiments.

• 

  Figure 3 Lung pathology in WT and Nod1-deficient mice infected with A. baumannii. Lung pathology in WT and Nod1-deficient mice (n=5–6 mice per group) infected with A. baumannii was evaluated in H&E-stained section (A, ×40 magnification). Histology score was calculated as described in Materials and Methods, and the results are shown as mean±SD (B).

• 

  Figure 4 Expression of β-defensins in the lungs of WT and Nod1-dificient mice infected with A. baumannii. RNA was obtained from the lungs of WT and Nod1-deficient mice (n=5–6 mice per group) infected with A. baumannii. The gene expressions of mBD-1, -2, -3, and -4 were examined by real-time PCR (A–D). Fold increase (arbitrary unit) was obtained by comparing each level in the lungs from infected to that in uninfected control lungs. *P<0.05 and **P<0.01.

• 

  Figure 5 Nod1 deficiency does not influence the production of cytokines by macrophages in response to A. baumannii. WT and Nod1-deficient bone marrow-derived macrophages (BMDMs) in triplicates were infected with indicated doses of A. baumannii for 24 h, and levels of IL-6 and TNF-α in culture supernatants were measured by ELISA (A and B). Results are from one of three independent experiments.

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