Some studies on experimental infection with Mycoplasma pneumoniae (M. pneumoniae) have been reported. However, these models were unable to appear the transitional changes of epithelial cells in respiratory tract. In the present study, the tracheal rings of human embryo were used in organ culture for the purpose of continual observation on the host-parasite relationship in respiratory tract of man. In this system, distinct cytopathology was found to appear not only by isolated strains but also by standard strain (Mac strain) which was not able to produce effective damage to epithelium in hamster tracheal organ culture system. This observation suggest that precise virulence of M. pneumoniae strain was detectable only by experimental infection used epithelial cells of human respiratory tract. By the immunofluorescent technique, specific fluorescence was proved in the epithelial cytoplasma and covered fluorescent material was found on epithelial surface of infectious tracheal rings. In the electron microscopic findings, many infectious ciliated epithelial cells lost most of their cilia and some of remained cilias were metamorphosed. Microvillies of cells appeared as short rounded projections. Numerous rounded bodies which had about 150mμ. Diameter were found on the luminal border of cells and in the intercellular spaces but these structures were not found in the intracellular. Relationship between M. pneumoniae and the epithelial cell which was demonstrated by the results of immunofluorescence and electron microscopy may have implications for further understanding of M. pneumoniae infections.
After a strain of mumps virus was serially passaged in the amniotic cavity of chick embryo, it was tested for the grade of attenuation and reactogenicity as a live mumps virus vaccine in volunteered children who had been seronegative to mumps virus. The vaccines prepared at the 4th, 6th, 9th, 15th, 21st, and 26th passage levels respectively were inoculated into different groups of those children. No clinical manifestations were observed after vaccination and the vaccines from the 4th, 6th, 9th, 15th passage level elicited an antibody response in all the vaccinees. However, the seroconversion rate decreased gradually as the passage level increased, those of 21st and 26th levels being 86% and 75%, respectively. Then the plaque cloning was carried out using the 6th passage level (U-1005) virus: six clones were selected by the different plaque size on the chick embryo fibroblast cells. When six vaccine preparations prepared from those clones were compared, the seroconversion rates of U-1005-1, U-1005-2, and U-1005-9 clone vaccines were 97.4%, 95.8% and 97.5% respectively and they gave the geometric mean neutralizing antibody titer of 8.1, 9.9 and 6.3 respectively. In order to test influences of the futher passage on antibody response, U-1005-9 strain was passaged up to 10th in chick amniotic cavity. When examined at 5th and 10th passage levels, it was proved stable concerning clinical reaction as well as antibody response.