To investigate the effect of high mobility group box 1 (HMGB1) / Toll-like receptor 4 (TLR4) signaling pathway on rats with acute lung injury induced by sepsis.

A total of 60 clean male Sprague Dawley rats were randomly divided into a sham operation group, a sepsis group and an experimental group, with 20 rats in each group. Rats in the sham operation group received celiotomy, and rats in the sepsis group and experimental group were injected with isotonic NaCl solution (4 mL / kg) and anti-HMGB1 monoclonal antibody (2 mg / kg) respectively via caudal vein 0.5 h after cecal ligation and puncture (CLP). Ten rats in each group were used to observe the survival status 7 d after CLP, and the others were sacrificed to take lung tissue samples 24 h after CLP. The Smith score of lung injury was calculated, and the expression levels of HMGB1 and TLR4 positive proteins in the lung tissue were compared among the three groups. The levels of tumor necrosis factor-alpha (TNF-α), interleukin-6 (IL-6), HMGB1 and TLR4 in bronchoalveolar lavage fluid (BALF) were measured by the enzyme-linked immunosorbent assay, the phagocytosis of alveolar microphage (AM) was compared by counting the number of microglobulins in each AM, and the expression levels of HMGB1 and TLR4 proteins in AM were determined by Western-blotting.

On 7 d after CLP, rats in the sham operation group all survived, while three rats in the sepsis group and five rats in the experimental group survived. The survival status of rats among the three groups was significantly different ( χ² = 10.833, P = 0.004), and it was better in the sham operation group than in the sepsis group and experimental group (both P < 0.017), but no significant difference was noted between the latter two groups (P = 0.120). The Smith score of lung injury [(2.20 ± 0.27), (8.20 ± 1.27), (4.25 ± 2.21); F = 56.432, P < 0.001], HMGB1 [(10.4 ± 1.5), (34.4 ± 5.0), (26.6 ± 6.9); F = 35.203, P = 0.003] and TLR4 [(10.6 ± 2.1), (48.0 ± 5.8), (38.2 ± 5.3); F = 103.414, P = 0.002] positive proteins in the lung tissue, TNF-α [(19 ± 4), (45 ± 4), (35 ± 4) μg / L; F = 2.749, P < 0.001], IL-6 [(56 ± 19), (86 ± 15), (70 ± 19) μg / L; F = 4.648, P = 0.001], HMGB1 [(41 ± 18), (70 ± 15), (56 ± 12) μg / L; F = 7.254, P = 0.002] and TLR4 [(20.9 ± 1.8), (51.2 ± 1.6), (49.8 ± 2.6) μg / L; F = 3.978, P = 0.035] in BALF, phagocytosis of AM [(21.8 ± 2.7), (3.1 ± 1.9), (12.6 ± 2.2); F = 32.821, P = 0.001], and HMGB1 [(11 ± 3), (40 ± 15), (24 ± 13); F = 7.253, P < 0.001] and TLR4 [(0.9 ± 0.4), (1.2 ± 0.6), (1.1 ± 0.4); F = 3.984, P = 0.028] proteins in AM were significantly different among the sham operation group, sepsis group and experimental group. Further pairwise comparison revealed that the Smith score of lung injury, HMGB1 and TLR4 positive proteins in the lung tissue, TNF-α, IL-6 and HMGB1 in BALF, and HMGB1 protein in AM in the sepsis group and experimental group were higher than those in the sham operation group, and they were highest in the sepsis group (all P < 0.05). The phagocytosis of AM in the sepsis group and experimental group was worse than that in the sham operation group, and it was worst in the sepsis group (all P < 0.05). The levels of TLR4 in BALF and TLR4 protein in AM in the sepsis group and experimental group increased obviously as compared with those in the sham operation group (all P < 0.05), while no difference was noted between the former two groups (both P > 0.05).

Inhibition of the HMGB1 / TLR4 signaling pathway can reduce the inflammatory response, prevent the excessive release of inflammatory mediators, and enhance the phagocytic function of AM in rats with lung injury induced by sepsis.