The expression of PDGF-B chain mRNA in lung tissue from rats repeatedly infected with mycoplasma pneumoniae

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 erythrornycin (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.

Keywords

mycoplasma pneumoniae / pulmonary interstitial fibrosis / platelet derived growth factor-BB

References

[1] 1996, 25:154

[2] WestermarkB. The molecular and cellular biology of platelet-derived growth factor. Acta Endocrinol, 1990, 123131-131

[3] 1996, 25: 39

[4] 1992, 15: 14

[5] AntoniadesH N, BravoM A, AvilaR E, et al. . Platelet-derived growth factor in idiopathic pulmonary fibrosis. J Clin Invest, 1990, 861055-1055

[6] VignaudJ M, AllamM, MartinetN, et al. . Presence of platelet-derived growth factor in normal and fibrotic lung is specifically associated with interstitial macrophages, while both interstitial and alveolar epithelial cells express the c-sis protooncogene. Am J Respir Cell Mol Biol, 1991, 5531-531

[7] HommaS, NagaokaI, AbeH, et al. . Localization of platelet-derived growth factor and insulin-like growth factor-1 in the fibrotic lung. Am J Respir Crit Care Med, 1995, 1522084-2084

[8] AubertJ D, PareP D, HoggJ C, et al. . Plateletderived growth factor in bronchiolitis obliteransorganizing pneumonia. Am J Respir Crit Care Med, 1997, 155676-676

[9] HerzM I, HenkeC A, NaklethR E, et al. . Obliterative bronchiolitis after lung transplantation: a fibroproliferative disorder associated with platelet-derived growth factor. Proc Natl Acad Sci USA, 1992, 8910-385

[10] Rojas-valenciaL, MontielF, MontanoM, et al. . Expression of a 2. 8-kb PDGF-B/c-sis transcript and synthesis of PDGF-like protein by human lung fibroblasts. Chest, 1995, 108240-240