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The expression of PDGF-B chain mRNA in lung tissue from rats repeatedly infected with mycoplasma pneumoniae
1Department of General Medicine, Tongji Hospital, Tongji Medical University, Wuhan.
Abstract:
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 bronchoalveolar 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, P < 0.05) and in BALF from those rats both infected with MP and, at the same time, treated with erythromycin (n = 4, P < 0.05). Bacterial cultures of the bronchial and lung tissue were negative in all three groups. The observation under a transmission electron microscope indicated that the interalveolar septa were widened with increased amount of collagen in the MP-infected rats while there were no obvious abnormalities in the other two groups. (2) Strong positive expression of PDGF-B chain mRNA was found in the plasma of monocytes and macrophages located in the locally widened interalveolar septa and alveolar spaces in the lung tissue from the MP-infected animals with the integral optical densities being 37.42 +/- 9.05 (n = 4) which was significantly higher than the values of control group (0.42 +/- 0.08, n = 4, P < 0.01) and of the group with MP-infection plus erythromycin treatment (1.62 +/- 0.40, n = 4, P < 0.01). These results suggest that PDGF-BB may be involved in the process of the development of pulmonary interstitial fibrosis caused by the repeated MP-infection. It may be an important growth factor for mediating the roles of monocytes and macrophages to promote the aggregation and proliferation of fibroblasts which can then secrete collagen in large quantity in the pulmonary interstitium.
Insights
Platelet-derived growth factor-BB (PDGF-BB) plays a role in developing pulmonary interstitial fibrosis after repeated Mycoplasma pneumoniae (MP) infections in rats. This growth factor may mediate monocyte and macrophage actions, promoting fibroblast proliferation and collagen secretion.
Area of Science:
- Pulmonary Medicine
- Pathology
- Molecular Biology
Background:
- Recurrent Mycoplasma pneumoniae (MP) infections can lead to pulmonary interstitial fibrosis.
- The specific molecular mechanisms driving this fibrotic process require further elucidation.
Purpose of the Study:
- To investigate the role of platelet-derived growth factor-BB (PDGF-BB) in the pathogenesis of pulmonary interstitial fibrosis induced by repeated MP infections in a rat model.
- To examine the expression of PDGF-B chain mRNA in lung tissue following MP infection.
Main Methods:
- A rat model of pulmonary interstitial fibrosis was established through repeated ultrasonic nebulizing inhalation of MP over 24 weeks.
- In situ hybridization with a PDGF-B chain cDNA probe was used to quantify PDGF-B chain mRNA expression in lung tissue.
- Transmission electron microscopy was employed to assess structural changes in lung tissue.
Main Results:
- Repeated MP infection led to widened interalveolar septa and increased collagen deposition, indicative of fibrosis.
- Significantly elevated PDGF-B chain mRNA expression was observed in monocytes and macrophages within the fibrotic lung tissue of MP-infected rats compared to controls and erythromycin-treated groups.
- MP was detected in bronchoalveolar lavage fluid of infected rats but not in controls or those treated with erythromycin, with negative bacterial cultures in all groups.
Conclusions:
- PDGF-BB is implicated in the development of pulmonary interstitial fibrosis following repeated MP infections.
- PDGF-BB may act as a key growth factor, influencing monocytes and macrophages to promote fibroblast proliferation and subsequent collagen deposition in the pulmonary interstitium.
