Complement activation and stimulation of chemotaxis by Chlamydia trachomatis.

The stimulus for the migration of polymorphonuclear leukocytes (PMNs) in acute chlamydial infection was studied in vitro by examining the chemotaxigenic effect of L2 and DE Chlamydia trachomatis elementary bodies (EB) upon the plasma of three healthy donors. In each individual experiment, chemotactic response was assessed with PMNs and plasma from the same respective donor, and no specific antibodies against C. trachomatis were detected in the plasma of any donor. Chemotaxis was observed in an agarose plate assay and was quantitated as the chemotactic differential, or CD (directed migration of PMNs minus random movement of PMNs). For each donor, the mean CD was significantly greater (P less than 0.005) when plasma preincubated for 2 h with L2 EB was used as the chemoattractant than when (i) plasma alone, (ii) plasma preheated to 56 degrees C for 30 min before incubation with L2 EB, or (iii) L2 EB in phosphate-buffered saline (PBS) was used as the potential chemoattractant. Similarly, in the one donor in whom DE EB were studied, the mean CD was also significantly greater (P less than 0.005) for plasma preincubated with DE EB as compared with (i) plasma alone or (ii) DE EB in PBS. Complement activation by C. trachomatis EB was assessed by radioimmunoassay for C5a des-arginine in all chemoattractant preparations used in the chemotaxis assay. Mean C5a des-arginine levels were high in plasma samples preincubated with L2 EB (171.00 +/- 10.64, 107.00 +/- 4.76, and 89.70 +/- 1.74 ng per ml) or DE EB (37.40 +/- 15.76 ng per ml) but were undetectable (less than 4.0 ng per ml) in (i) plasma alone, (ii) preheated plasma incubated with L2 EB, and (iii) PBS containing L2 EB. Thus, L2 EB and DE EB of C. trachomatis exert a chemotaxigenic effect upon normal antibody-negative plasma, and this effect is at least in part a result of complement activation and generation of the potent chemotaxin C5a.