Influence regulation of inflammatory immune response by interleukin-17 lipopolysaccharide-induced acute lung injury in mice

Abstract

To explore the immunomodulatory effects of interleukin-17 (IL-17) on acute lung injury (ALI) induced by lipopolysaccharide (LPS). Thirty-six SPF-class C57BL/6 mice were divided into normal saline control group (NS group) and LPS-induced ALI model group (LPS group, LPS 5 mg/kg intratracheal drip) according to random number table method, with 18 mice in each group. Six mice were sacrificed at 2, 6 and 24 hours after model reproduction, and peripheral blood, lung and spleen tissues were harvested. After staining with hematoxylin-eosin (HE), the pathological changes of lung tissue were observed under microscope and the infiltration level of lymphocytes, neutrophils and macrophages in the alveolar wall and tracheal wall were detected. Immunohistochemistry was used to detect the protein expression of IL-17 in alveolar wall and tracheal wall, and the correlation between IL-17 expression and lymphocytes, neutrophils and macrophages infiltration in alveolar wall and tracheal wall were analyzed. The level of IL-17 in lung tissue homogenate was determined by enzyme linked immunosorbent assay (ELISA). Flow cytometry was used to detect the proportion of CD4+IL-17+ helper T cells (Th17 cells) in CD4+ T cells in peripheral blood, lung tissue and spleen tissue. (1) Microscopy showed that the lung tissue structure of NS group was basically normal at each time after model reproduction, and there was no obvious inflammatory cell infiltration, while the lung tissue edema and inflammatory reaction were gradually aggravated in the LPS group, and the lung injury score was significantly higher than that in NS group at each time (2 hours: 4.47±1.42 vs. 1.10±0.55, 6 hours: 7.93±2.14 vs. 1.23±0.50, 24 hours: 12.67±2.67 vs. 1.20±0.61, all P < 0.01). (2) Immunohistochemistry showed that the protein expression of IL-17 in alveolar wall and tracheal wall of LPS group increased gradually with time, while that in NS group was negative or weak positive. Quantitative analysis showed that the immunohistochemical staining score of IL-17 protein in alveolar wall and tracheal wall of LPS group were higher than those of NS group (alveolar wall: 2.70±1.40 vs. 0.90±0.37 at 2 hours, 5.10±1.76 vs. 1.17±0.59 at 6 hours, 9.67±1.32 vs. 1.10±0.45 at 24 hours; tracheal wall: 2.87±0.89 vs. 0.90±0.39 at 2 hours, 4.97±1.48 vs. 1.10±0.41 at 6 hours, 8.67±1.54 vs. 1.03±0.29 at 24 hours; all P < 0.05). (3) Correlation analysis showed that the protein expression of IL-17 in alveolar wall and tracheal wall were positively correlated with the degree of lymphocyte, neutrophil and macrophage infiltration (alveolar wall: r value was 0.632, 0.550, 0.466; tracheal wall: r value was 0.695, 0.662, 0.575, respectively; all P < 0.01). (4) IL-17 content (μg/L) in lung tissue homogenate was significantly higher than that in NS group at each time after model reproduction (2 hours: 1.37±0.14 vs. 1.01±0.18, 6 hours: 1.65±0.19 vs. 1.11±0.18, 24 hours: 1.92±0.36 vs. 1.17±0.24, all P < 0.01). (5) The proportion of Th17 cells in the peripheral blood, lung tissue and spleen tissue of the LPS group were higher than those of the NS group at each time after model reproduction [peripheral blood: (2.62±0.62)% vs. (1.42±0.40)% at 2 hours, (3.74±0.43)% vs. (1.27±0.32)% at 6 hours, (4.44±0.65)% vs. (1.59±0.45)% at 24 hours; lung tissue: (2.32±0.44)% vs. (1.50±0.25)% at 2 hours, (3.66±0.36)% vs. (1.33±0.24)% at 6 hours, (4.60±0.54)% vs. (1.60±0.27)% at 24 hours; spleen tissue: (1.49±0.36)% vs. (0.69±0.21)% at 2 hours, (2.58±0.55)% vs. (0.59±0.18)% at 6 hours, (3.76±0.57)% vs. (0.65±0.26)% at 24 hours; all P < 0.01]. IL-17 is involved in the inflammatory immune regulation of ALI mice.