HEPARIN-MEDIATED INHIBITION OF CHLAMYDIA-PSITTACI ADHERENCE TO HELA-CELLS

The adherence of human strains of Chlamydia trachomatis has been recen tly shown to be inhibitable by heparin and heparitinase, leading to th e proposal that Chlamydia binding to host cells may be mediated by a g lycosaminoglycan (GAG)-dependent mechanism. We here describe the adher ence of the guinea-pig pathogen, Chlamydia psittaci GPIC, to HeLa cell s, which was measured by cytofluorometry with chlamydiae whose DNA was fluorescently labelled. Adherence could be inhibited by heat or tryps in pretreatment of the bacteria, and binding was much faster at 37 deg rees C (reaching a plateau within 1 h) than 4 degrees C. Little bindin g remained when host cells were pre-fixed with paraformaldehyde, sugge sting that host cell receptor mobility may be required for effective a dherence. Visualization by confocal microscopy confirmed that the bact eria were at or near the host cell surface during the entire time-cour se of these experiments. Adherence increased as a function of pH betwe en pH 6 and pH 8.0-8.5. Both adherence and infection of HeLa cells cou ld be inhibited with heparin when the adherence step was performed at 4 degrees C, but only infection was inhibited when the adherence step was performed at 37 degrees C, even though heparitinase could block ad herence at either 4 degrees C or 37 degrees C. Even at 4 degrees C, he parin-mediated inhibition was significantly lower at pH 8 than pH 7.4, suggesting that GAG-independent mechanisms may play a role in the hig her adherence observed at basic pH. These results therefore demonstrat e that a GAG-dependent adherence step may be operative in C. psittaci, and raise the possibility that other adherence mechanisms may also co ntribute to binding by this chlamydial strain. Furthermore, they sugge st that there may not be a strict correlation between C. psittaci adhe rence and the ability to cause productive infections. (C) 1997 Academi c Press Limited