Abstract: Objective To investigate the effects of different doses of methylprednisolone on Toll-like receptor 4(TLR4)/nuclear factor κB (NF-κB) pathway in lung tissue of mouse model with Mycoplasma pneumoniae pneumonia. 
Methods  Forty healthy male SD mice were selected, of which 10 were randomly selected as normal mice group, and the remaining 30 were used to establish mouse model of Mycoplasma pneumoniae pneumonia. After successful modeling, 10 were randomly selected as model group, and the remaining 20 were selected as low-dose intervention group and high-dose intervention group. Low-dose intervention group was injected with low-dose methylprednisolone, while high-dose intervention group was injected with high-dose methylprednisolone. The expression of TLR4 and NF-κB was compared among groups. The levels of TLR4 and NF-κB were detected by immunohistochemistry. The levels of tumor necrosis factor-α(TNF-α) and interleukin 1β(IL-1β) were detected by enzyme-linked immunoassay. Superoxide dismutase(SOD) was detected by xanthine oxidase method and malondialdehyde(MDA) was detected by thiobarbituric acid method. 
Results Compared with normal mice group, the expression of TLR4 and NF-κB was higher in model group, low-dose intervention group and high-dose intervention group, the expression of TLR4 and NF-κB in low-dose intervention group and high-dose intervention group was lower than that in model group, and the expression of TLR4 and NF-κB in high-dose intervention group was lower than that in low-dose intervention group(P＜0.05). Compared with normal mice group, the expression of TLR4 and NF-κB in model group, low-dose intervention group and high-dose intervention group was higher.The levels of TLR4 and NF-κB were lower in the low-dose intervention group and the high-dose intervention group than in the model group, and the levels of TLR4 and NF-κB in the high-dose intervention group were lower than those in the low-dose intervention group(P＜0.05). Compared with the normal mice group, the levels of TNF-α and LI-1β in the model group. The low-dose intervention group and the high-dose intervention group was higher, and the levels of TNF-α and LI-1β in the low-dose intervention group and the high-dose intervention group were lower than those in the model group. The level of TNF-α and IL-1β in the high-dose intervention group was lower than that in the low-dose intervention group(P＜0.05). Compared with the normal mice group, the MDA level was higher and SOD level was lower in the model group, the low-dose intervention group and the high-dose intervention group. The MDA level was lower and SOD level was higher in the low-dose intervention group and the high-dose intervention group, as compared with the model group, and the MDA level was lower and SOD was higher in the high-dose intervention group than in the low-dose intervention group(P＜0.05). 
Conclusion In mouse model of Mycoplasma pneumoniae pneumonia, methylprednisolone can significantly improve the lung tissue damage, inhibit the expression of TLR4/NF-κB pathway, reduce the degree of inflammatory response, and improve oxidative stress, and the high-dose effect is more significant.

Key words: pneumonia, mycoplasma, methylprednisolone, malondialdehyde