OBJECTIVE To explore the causative agents of the atypical pneumonia (also SARS) occurred recently in some regions of our country. METHOD Organ samples of 7 dead cases of SARS were collected from Guangdong, Shanxi, Sichuan Provinces and Beijing for electron microscopic examination. 293 cell line was inoculated with the materials derived from the lungs to isolate causative agent(s). The agents in the organs and cell cultures were revealed by immunoassay. RESULTS Both Chlamydia-like and coronavirus-like particles were found in EM. Inclusion bodies containing elementary bodies, reticulate antibodies and intermediate bodies of Chlamydia-like agent were visualized in multiple organs from the 7 dead cases, including lungs (7 cases), spleens (2 cases), livers (2 cases), kidneys (3 cases) and lymph nodes (1 cases), by ultrathin section electron microscopy (EM). In some few sections, coronavirus-like particles were concurrently seen. A coronavirus RNA- polymerase segment (440 bp) was amplified from the lung tissues of two cases of the SARS. After inoculated with materials from the lung samples, the similar Chlamydia-like particles were also found in the inoculated 293 cells. Since the Chlamydia-like agents visualized in both organs and cell cultures could not react with the genus specific antibodies against Chlamydia and monoclonal antibodies against C. pneumoniae and C. psittaci, the results might well be suggestive of a novel Chlamydia-like agent. CONCLUSION Since the novel Chlamydia-like agent was found co-existing with a coronavirus-like agent in the dead cases of SARS, it looks most likely that both the agents play some roles in the disease. At the present time, however, one can hardly determining how did these agents interact each other synergetically, or one follows another, need further study.
[Chlamydia-like and coronavirus-like agents found in dead cases of atypical pneumonia by electron microscopy].