Establishment of a mouse pneumonia model for Mycoplasma pncumoniae infection and alterations on the level of IFN-γ

To establish a mouse pneumonia model for Mycoplasma pneumoniae infection to study the changes of level of IFN-γ,BALB/c mice were randomly grouped by body weight,and instillated intranasally with bacterial suspension of M.pneumoniae on day 0,1 and 2 mean while the control group was set up with instillation of sterile broth intranasally.Mice were sacrificed on 1-21 days.And detection of the M.pneumoniae by culture and PCR tesing in the lung tissues of mice were performed.A histopathological scoring system adapted from a hamster model of M.pneumoniae was applied to judge the severity of the inflammatory reactions of lungs,and the lung specimens were evaluated for the percentages of the involved sites with peribrochiolar infiltrates,quality of infiltrales.Luminal exudates,perivascular infiltrates and parenchymal pneumonia,to define the inflammatory reactions in the lumgs on a scale of 0-26 (from least to most severity).The level of IFN-γ was determined by ELISA on 1,3,4,6,8 and 14 days after infection.The experimental results showed that the pulmonary inflammation occurred on day 1 after inoculation/l of M.pneumoniae,and the average score of the histopathological scoring of lesions was 6.32,and showed the most severe lesions on day 3 and 4 with the average score of 11.6 and 9.58 respectively,and the highest score of 19.It became less severe later on,and on day 21 the inflammatory reactions almost disappeared.The control group showed no any inflammatory reactions in lungs.There were evidences of existence of M.pneumoniae by culture and PCR testing in the lung tissues with a detection rate of 100%.On day 1,2,3,and 4.The level of IFN-γ in blood serum had been examined by ELISA On day 1,3,4,6,8 and 14,and it was found that the level of IFN-γ was significantly decreased on day 3 and 4,and then gradually returmed to normal up to 6 days.It concludes that there are marked pathological changes of pneumonija after 3 days intranasal instillation of bacterial suspension of M.pneumonia,in association with reduction of the level of IFN-γ in blood serum of infected mice,and the histopathological scoring system can be used to determine the severity of acute inflammatory lesions of lung of BALB/c mice.