TLR2 regulates allergic airway inflammation through NF-κB and MAPK signaling pathways in asthmatic mice

OBJECTIVE: To investigate the role of toll-like receptor 2 (TLR2) in asthmatic mouse model and its possible signal transduction pathways.

MATERIALS AND METHODS: Mice were divided into three groups: TLR2-/- asthma mouse model group (n=10), C57BL/6 asthma mouse model group (n=10) and control group (n=10). Mice were sensitized and stimulated with ovalbumin (OVA) to establish the asthmatic mouse model. The unilateral bronchoalveolar lavage fluid (BALF) was collected and centrifuged to separate cells, and the cells were classified and counted via smear test under a microscope. Part of the lung tissues on the other side was taken for hematoxylin-eosin (HE) staining to observe the histopathological change in lung tissues. The remaining lung tissues on the other side were taken to detect the messenger ribonucleic acid (mRNA) expression levels of interleukin-4 (IL-4), IL-5 and IL-13 via reverse transcription-polymerase chain reaction (RT-PCR). The levels of nuclear factor-κB (NF-κB) p65, phosphorylated (p)-NF-κB p65, p-IκBα, extracellular signal-regulated kinase (ERK)1/2, p-ERK1/2, Jun N-terminal kinase (JNK), p-JNK, p38 mitogen-activated protein kinase (MAPK), p-p38 MAPK, IL-4, IL-5 and IL-13 were detected via enzyme-linked immunosorbent assay (ELISA). The protein expressions of NF-κB p65, p-NF-κB p65, p-IκBα, ERK1/2, p-ERK1/2, JNK, p-JNK, p38 MAPK, and p-p38 MAPK were detected using the immunohistochemical method.

RESULTS: HE staining showed that the infiltration degree of inflammatory cells in perivascular tissues in TLR2-/- asthma group was reduced compared with that in C57BL/6 asthma group. Results of electron microscopy showed that the ultrastructural changes in alveolar type I epithelial cells in mice in TLR2-/- asthma group was significantly alleviated. In BALF in TLR2-/- asthma group, the numbers of eosinophils and lymphocytes were significantly decreased, but the number of macrophages was significantly increased compared with those in C57BL/6 asthma group. Results of RT-PCR and ELISA revealed that the mRNA and protein expression levels of IL-4, IL-5, and IL-13 in lung tissues of mice in TLR2-/- asthma group were significantly decreased compared with those in C57BL/6 asthma group. Besides, results of ELISA and immunohistochemistry revealed that the protein expressions of NF-κB p65, p-NF-κB p65, p-IκBα, ERK1/2, JNK, p38 MAPK, p-ERK1/2, p-JNK, and p-p38 MAPK in lung tissues of mice in TLR2-/- asthma group were significantly decreased compared with those in C57BL/6 asthma group.

CONCLUSIONS: TLR2 is involved in the occurrence and development of experimental asthmatic airway inflammation. TLR2 gene knockout in asthmatic mice can alleviate the airway inflammation, whose mechanism may be that the allergic airway inflammation of asthmatic mice is alleviated through inhibiting NF-κB and MAPK signaling pathways.

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