Comparison of Chlamydia pneumoniae isolates by western blot (immunoblot) analysis and DNA sequencing of the omp 2 gene.

The 60-kDa cysteine-rich outer membrane protein gene (omp 2) from nine Chlamydia pneumoniae isolates (TW-183, CM-1, CWL-050, CWL-011, IOL-207, FIL, Kajaani-6, Helsinki-12, and Parjaanonen) was amplified by PCR and sequenced from positions 1 to 580. In contrast to the sequence differences previously observed in this gene in other chlamydial species, all nine C. pneumoniae isolates were 100% identical. However, when sera from C. pneumoniae microimmunofluorescence-positive patients (with clinical signs of persistent cough or asthma) were immunoblotted against five C. pneumoniae isolates, distinct antigenic differences were observed. TW-183 was characterized by major bands at 35 and 43 kDa. In contrast, the other four isolates tested produced similar, though not identical, immunoblot profiles, characterized by strong bands at 18, 25, 29, 40, 46, and 53 kDa. These data support the fact that significant differences do exist between C. pneumoniae isolates, but unlike the case with other chlamydial species, these differences do not reside in either of the commonly studied outer membrane protein genes, omp 1 or omp 2.