Differential expression of three Chlamydia trachomatis hsp60-encoding genes in active vs. persistent infections

Real time RT-PCR was used to assess expression of the three Chlamydia trachomatis hsp60-encoding genes (Ct110, Ct604, Ct755) over time in in vitro systems of active vs. persistent infection, and in synovial samples from patients with Chlamydia-induced arthritis. In HEp-2 cells actively infected with C. trachomatis (serovar K), mRNA from Ct110 (groEL) was apparent by 8 h post-infection (p.i.) and increased more than 10-fold through 48 h p.i.; mRNA from Ct604 followed a similar pattern. Transcripts from Ct755 were abundant at 8 h p.i. and remained 2-3-fold higher than those from Ct110 at all times. In persistently infected human monocytes in culture, expression of Ct110 and Ct755 was low from 1 to 7d p.i., while mRNA from Ct604 was abundant at 1d p.i. and increased more than 3-fold from 1 to 3d p.i., as the organism transited to the persistent state. Those mRNA levels remained high through 7d p.i. Real time analyses of RNA/cDNA from synovial tissue of patients with Chlamydia-associated arthritis showed high Ct604 mRNA levels, consistent with results from the in vitro monocyte system of persistence. These data demonstrate that each chlamydial hsp60-encoding gene is expressed independently, and that the three genes are expressed differentially in active vs. persistent infection. The results further suggest that the Ct604 gene product may function importantly during chlamydial persistence.