In order to investigate the role played by platelet derived growth factor-BB (PDGF-BB) in the pathogenesis of pulmonary interstitial fibrosis in rats repeatedly infected with mycoplasma pneumoniae (MP), a rat MP infection model was developed by infecting rats with MP for 9 times during a period of 24 weeks with a technique of ultrasonic nebulizing inhalation. Then in situ hybridization was performed with PDGF-B chain cDNA probe and the results were quantitatively analyzed to measure the changes in PDGF-B chain mRNA expression in the lung tissue. The results showed that: (1) MP polymerase chain reaction (PCR) tests showed positive results in the bronchoalveotar lavage fluid (BALF) from all of the MP-infected rats (n=4) while they were all negative in BALF from the control animals (n=4, P0.05) and in BALF from those rats both infected with MP and, at the same time, treated with erythromycin (n=4, P0.05). Bacterial cultures of the bronchial and lung tissue were negative in all three groups. The
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