Role of transiently accumulated neutrophils in the lung of hamster in development of pneumonia due to Mycoplasma pneumoniae

: The importance of Mycoplasma pneumoniae as a pathogen of human infectious diseases, particularly of respiratory infections, has been well recognized. However, the details of the mechanism through which lung tissue damages are produced in mycoplasmal infection has not been fully understood. It has been pointed out that beside the direct invasive process certain immunological responses to the deposited microbes are crucial in development of mycoplasmal pneumonia. In the present study, we aimed at elucidating the role of neutrophils in producing pneumonia due to Mycoplasma pneumoniae in hamsters. For this purpose, hamsters were divided into two groups; the one not pretreated and infected with Mycoplasma pneumoniae and the other immunosuppressed by 60Co irradiation and infected. A serial determination of the numbers of mycoplasmal cells recovered from the treacheal tissue and bronchoalveolar lavage fluid (BALF) and analysis of cellular components in BALFs were carried out. The severity and the nature of pathological changes produced in the lungs were evaluated and scored on the basis of microscopic findings. As a result, it was found that the numbers of mycoplasmal cells recovered from both tracheal tissues and BALFs reached maximum on the seventh day of infection in both groups and decreased rapidly. There no apparent difference was found between the two groups in number of cells recovered. In the not-irradiated control groups, the percentage of polymorphonuclear leukocytes (PMNs) in BALF was very high on the seventh day and then they were replaced by lymphocytes by the 21st day of infection.(ABSTRACT TRUNCATED AT 250 WORDS)