[Heme oxygenase-1 (HO-1) gene knockout affects the balance of lung immune cell composition and aggravates inflammatory injury in lung tissues of LPS-induced acute lung injury (ALI) mice].

Objective To evaluate the effects of heme oxygenase-1 (HO-1) gene deletion on immune cell composition and inflammatory injury in lung tissues of mice with lipopolysaccharide (LPS)-induced acute lung injury (ALI). Methods C57BL/6 wild-type (WT) mice and HO-1 conditional-knockout (HO-1^-/-) mice on the same background were randomly divided into four groups (n=5 in every group): WT control group, LPS-treated WT group, HO-1^-/- control group and LPS-treated HO-1^-/- group. LPS-treated WT and HO-1^-/- groups were injected with LPS (15 mg/kg) through the tail vein to establish ALI model, while WT control group and HO-1^-/- control group were injected with an equivalent volume of normal saline through the tail vein, respectively. Twelve hours later, the mice were sacrificed and lung tissues from each group were collected for analysis. Histopathological alterations of lung tissues were assessed by HE staining. The levels of mRNA expression of tumor necrosis factor α (TNF-α), interleukin 1β (IL-1β), and IL-6 were determined by PCR. The percentages of neutrophils (CD45⁺CD11b⁺Ly6G⁺Ly6C^-), total monocytes (CD45⁺CD11b⁺Ly6C^hi), pro-inflammatory monocyte subsets (CD45⁺CD11b⁺Ly6C^hiCCR2^hi) and total macrophages (CD45⁺CD11b⁺F4/80⁺), M1 macrophage (CD45⁺CD11b⁺F4/80⁺CD86⁺), M2 macrophage (CD45⁺CD11b⁺F4/80⁺CD206⁺), total T cells (CD45⁺CD3⁺), CD3⁺CD4⁺ T cells, CD3⁺CD8⁺ T cells and myeloid suppressor cells (MDSCs, CD45⁺CD11b⁺Gr1⁺) were detected by flow cytometry. Results Compared with the corresponding control groups, HE staining exhibited increased inflammation in the lung tissues of both LPS-treated WT and HO-1^-/- model mice; mRNA expression levels of TNF-α, IL-1β and IL-6 were up-regulated; the proportions of neutrophils, total monocytes, pro-inflammatory monocyte subsets, MDSCs and total macrophages increased significantly. The percentage of CD3⁺, CD3⁺CD4⁺ and CD3⁺CD8⁺ T cells decreased significantly. Under resting-state, compared with WT control mice, the proportion of neutrophils, monocytes and pro-inflammatory monocyte subset increased in lung tissues of HO-1^-/- control mice, while the proportion of CD3⁺ and CD3⁺CD8⁺ T cells decreased. Compared with LPS-treated WT mice, the mRNA expression levels of TNF-α and IL-1β were up-regulated in lung tissues of LPS-treated HO-1^-/- mice; the proportion of total monocytes, pro-inflammatory monocyte subsets, M1 macrophages and M1/M2 ratio increased greatly; the percentage of CD3⁺CD8⁺ T cells decreased significantly. Conclusion The deletion of HO-1 affects the function of the lung immune system and aggravates the inflammatory injury after LPS stimulation in ALI mice.