The roles of the TLR/NF‑κB signaling pathway in the mutual interactions between the lung and the large intestine

Abstract

The 'exterior-interior relationship between the lung and the large intestine' is a classical basic theory in Traditional Chinese Medicine. The present study aimed to investigate the roles of the toll like receptor/nuclear factor‑κB (TLR/NF‑κB) signaling pathway in the mutual interactions between the lung and the large intestine. A rat model of allergic asthma complicated with intestinal flora disorder was established by oral administration of Candida albicans and intraperitoneal injection with ovalbumin. The number of inflammatory cells and expression levels immunoglobulin (Ig)E, secretory IgA, interleukin (IL)‑4 and interferon‑γ in serum and bronchoalveolar lavage fluid were subsequently measured. Bacterial colonies and expression of 16S ribosomal DNA were studied in feces samples and pathological alterations of lung tissues were identified. Furthermore, the expression levels of genes associated with the TLR/NF‑κB signaling pathway in the lung and intestinal tissues were determined by reverse transcription‑quantitative polymerase chain reaction. The results of the present study indicated that, in the rat model of allergic asthma complicated with intestinal flora disorder, the expression levels of IL‑4 and IgE, and the numbers of inflammatory cells and C. albicans increased, and marked inflammatory cell infiltration was observed in lung tissues, suggesting that the animal model was successfully established. Furthermore, the present results revealed the mRNA expression levels of genes associated with the TLR/NF‑κB signaling (including myeloid differentiation primary response 88, TNF receptor associated factor 6 and β‑arrestin) were upregulated in both of the lung and intestinal tissues of the model group rats. Collectively, the results demonstrated that the TLR/NF‑κB signaling may serve roles in the mutual interactions between the lung and the large intestine, and TLR and NF‑κB may be potential targets for the treatment of lung diseases complicated with intestinal disorders.

Figure 1.

Pulmonary function determined by measuring the respiratory rate and Penh value. Data are presented as the mean ± standard deviation (n=10). *P<0.05 and **P<0.01 vs. the model rats; ^##P<0.01 vs. the normal rats.

Figure 2.

Histological examination of lung tissues with hematoxylin and eosin staining (top row magnification, ×100; bottom row magnification, ×400). Black arrows indicate the blood vessel; red arrows indicate the inflammatory cell infiltration; yellow arrows indicate the pulmonary alveol; green arrows indicate the pulmonary septum; blue arrows indicate the bronchus.

Figure 3.

ELISA assays. (A) sIgA in bronchoalveolar lavage fluid. (B) sIgA in intestinal mucosa. (C) IgE in serum. Data are presented as the mean ± standard deviation (n=10); *P<0.05 and **P<0.01 vs. the model rats; ^#P<0.05 and ^##P<0.01 vs. the normal rats. S, secretory; Ig, immunoglobulin.

Figure 4.

ELISA assays in BALF. Expression levels of (A) IL-4 and (B) IFN-γ in BALF. Data are presented as the mean ± standard deviation (n=10). *P<0.05 and **P<0.01 vs. the model rats; ^#P<0.05 and ^##P<0.01 vs. the normal rats. BALF, bronchoalveolar lavage fluid; IL-4, interleukin 4; IFN-γ, interferon-γ.

Figure 5.

Composition of the intestinal flora in the normal, model and positive groups.

Figure 6.

Results of reverse transcription-quantitative polymerase chain reaction analysis of expression levels of TLR-2, TLR-4, MyD88, TRAF6 and β-arrestin. Data are presented as the mean ± standard deviation (n=10). **P<0.01 vs. the model rats; ^##P<0.01 vs. the normal rats. TLR, toll like receptor; MyD88, myeloid differentiation primary response 88; TRAF6, TNF receptor associated factor 6.