Time course of cHtrA expression during C. trachomatis infection. The C. trachomatis-infected culture samples were processed at various times after infection (as indicated on the top) for immunofluorescence staining as described in Figure 1 legend. The mouse anti-cHtrA (a to h) and anti-CPAF (mAb 100a; i to p) were visualized with a goat anti-mouse IgG conjugated with Cy3 (red) while the chlamydial organisms were visualized with a rabbit anti-chlamydia antibody plus a goat anti-rabbit IgG-Cy2 conjugate (green). Note that cHtrA was first detected inside the chlamydial inclusions at 12 hours after infection [panel d, yellow (overlapping with organisms) & red (free of chlamydial organisms) arrowheads], similar to the detection of CPAF. However, cHtrA secretion into host cell cytosol was only detected 24 h after infection while secretion of CPAF was already obvious by 16 h post infection.