Study On The Effect Of S100A8,S100A9,TNF-α And IL-6 Levels In Serum And BALF Of Rat On The Severity Of Mycoplasma Pneumoniae Pneumonia

Background Mycoplasma pneumoniae pneumonia（MPP）,as a common disease of communityacquired pneumonia（CAP）,significantly increases the risk of morbidity and mortality in children with increasing prevalence.Therefore,the early determination of the severity of MPP has become an issue of widespread concern.In recent years,the role of S100 protein in diseases has received much attention and research,under this context,we conducted this experiment to study the establishment method of MPP mouse model with different severity,and to explore the changes of S100A8,S100A9,TNF-α,and IL-6 in serum and bronchoalveolar lavage fluid（BALF）of mice with MPP.And to analyze the relationship between the concentration of these four indexes and the severity of MPP,in order to provide a new idea for judging the severity of MPP in the early stage.Methods Mice were randomly divided into high dose group,low dose group,and control group.Method of endotracheal intubation for MP infection.Blood,BALF,and lung tissue samples were collected on the 1th,3th,5th days of modeling.The concentrations of S100A8,S100A9,TNF-α,and IL-6 in serum and BALF of mice were analyzed by enzyme-linked immunosorbent assay（Elisa）.The lung tissue of mice was stained with HE to evaluate the severity of MPP and the localization of S100A8 and S100A9 in lung tissue by immunohistochemical staining（IHC）.The lung tissue was stained by the TUNEL method to observe the apoptosis in lung tissue.Results（1）The clinical observation showed that the mice infected with MP were in poor spirit,slow to respond to external stimuli,and liked to condense in the cage’s corner,especially on the 3rd day in the high dose group.（2）Observing the gross lung specimens,it was found that the lung color of mice infected with MP darkened and there was obvious congestion and edema,and the high dose group was prone to congestion on both sides of the lungs,especially on the 3rd day.（3）The results of Elisa detection showed that compared with the control group,the levels of S100A8,S100A9,and TNF-α in serum increased on the 1st and 3rd day after infection,especially in the high dose group,especially on the 3rd day.IL-6 increased significantly on the 3rd and 5th days after infection.（4）The contents of various indexes in BALF increased in infected MP and increased significantly in high dose group.（5）HE staining of mouse lung tissue showed neutrophil,lymphocyte,and monocyte-macrophage infiltration in bronchi,perivascular,and lung tissue space,and occasional positive cell infiltration in alveoli.Through the lung histopathological analysis,compared with the control group,the pathological changes of lung tissue in the high dose group were obvious,especially on the 3rd day.The pathological score showed that the severity of MPP in the high concentration group was more serious than that in the low dose group at each time point.（6）The results of immunohistochemical qualitative analysis of S100A8 and S100A9 in lung tissue of mice infected with MP showed that S100A8 and S100A9（brown granules）were mainly distributed in the cytoplasm and interstitial space of lung tissue.（7）TUNEL staining analysis of lung tissue showed that compared with the control group,apoptosis increased in the lung tissue of mice infected with MP,and the apoptotic cells were mainly seen in bronchioles endothelial cells,alveolar epithelial cells and alveolar infiltrating cells,especially in the high dose group.Conclusion 1.MPP mouse models with different severity were successfully established.2.When MPP occurred,the concentrations of S100A8,S100A9,TNF-α and IL-6 in serum and BALF increased,and increase was related to the severity of MPP.3.S100A8 and S100A9 may be involved in the development’s regulation of MPP and have potential value as b iomarkers for clinical diagnosis of the occurrence,development and severity of MPP.