The aim of this study was to determine the relationship between the radiological pattern of Mycoplasma pneumoniae and the level of cell-mediated immunity of the host. Computed tomographic (CT) scans of the chest and the results of the purified protein derivative (PPD) test were studied during the acute stage of infection in 54 patients with M. pneumoniae pneumonia. The CT findings were used to divide the patients into two groups: one group had a predominance of nodular opacities with a

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... ular distribution (Group N; n=29); and the other showed a predominance of an airspace consolidation (Group C; n=25). Forty out of 54 subjects had negative tuberculin skin tests (<10 mm induration). The positive rate of PPD reaction was higher in Group N (13 out of 29) compared to Group C (1 out of 25) (p=0.0005); whilst pleural effusion appeared more frequently in Group C (10 out of 25) than in Group N (3 out of 29) (p=0.023). There was no significant difference between Groups N and C in white blood cell and lymphocyte counts, level of antibodies to M. pneumoniae in sera, and severity of the disease. These findings suggest that the characteristics of the host cell-mediated immunity might influence the pattern of pulmonary lesions in M. pneumoniae infection.