VIABILITY AND GENE-EXPRESSION IN CHLAMYDIA-TRACHOMATIS DURING PERSISTENT INFECTION OF CULTURED HUMAN MONOCYTES

The principal host cell for persistently infecting synovial Chlamydia trachomatis is the macrophage. During infection of human monocytes/mac rophages in culture this bacterium displays aberrant morphology and pr oduces no new elementary bodies, reflecting the situation in synovium. Here we investigate the metabolic status of C. trachomatis (serovar K ) during an extended infection of human peripheral monocytes in vitro. Using reverse transcription-polymerase chain reaction assays, we have shown that primary transcripts from the chlamydial rRNA operons are p resent throughout a 10-day course of infection. Other assays targeting mRNAs from chlamydial genes encoding r-proteins S5 and L5, the glycyl -tRNA synthetase, the 60-kDa cysteine-rich outer membrane protein, and the KDO transferase indicate that these messengers are also present t hroughout the entire 10-day period. The gene encoding the 57-kDa heat- shock protein (hsp60) is expressed by the bacterium throughout the 10- day infection of cultured monocytes, but transcript levels from the ge ne encoding the major outer membrane protein (omp1) appear to be atten uated. Western analyses targeting these latter proteins confirm the pr esence of the hsp60 gene product, and the virtual absence of major out er membrane protein, in chlamydia-infected cultured human monocytes. T hus, during extended infection of human monocytes in vitro, chlamydia are non-productive but transcriptionally active; the pattern of transc riptional activity reflects that known for persistent C. trachomatis i nfection in vivo in synovial tissue.