[Studies on Chlamydia pneumoniae, strain TWAR, infection. I. Experimental infection of C. pneumoniae in mice and serum antibodies against TWAR by MFA].

Six to seven-week-old ICR mice were inoculated intranasally with C. pneumoniae TW-183 strain and observed for sickness and death. The inoculated mice showed weakness within the 1st day and decrease in weight were observed, however, mice were cured within 7 days after inoculation. No death was observed. Histopathological studies of the mice lungs clearly revealed interstitial pneumonitis on the 3rd day and parenchymal pneumoniae on the 5th day after inoculation. Pathological changes were, however, improved in 10 to 14 days after inoculation. Inclusions were detected from the 1st to 10th day in broncho-epithelial cells and alveolar epithelial cells by DFA stain and TWAR specific monoclonal antibody. Serum antibodies, IgG and IgM, were assayed by microplate immunofluorescence antibody technique (MFA). From 7 to 14 days after inoculation, the titer of IgG rapidly increased and reached 1:4096 and then this titer level was maintained for 3 weeks and more. On the other hand, IgM was detected on 7th day and increased up to 1:16 on 14th day. However, the IgM titer declined within 1 month. To examine the specificity of the antibody titration, IgG in sera prepared against C. pneumoniae TW-183, C. psittaci Cal 10 and C. trachomatis L2 strains were assayed by MFA using in situ inclusions of each strain and compared. The results indicated that IgG titer in homologous combination between antigen and antiserum was always 2 times higher than that of heterologous combination, suggesting strongly that the chlamydial species responsible for the infection could be differentiated by the comparison of IgG titers obtained in the MFA titration.