Chlamydia-dependent biosynthesis of a heparan sulphate-like compound in eukaryotic cells

One hypothesis for the mechanism of chlamydial interaction with its eukaryo tic host cell invokes a trimolecular mechanism, whereby a Chlamydia-derived glycosaminoglycan bridges a chlamydial acceptor molecule and a host recept or enabling attachment and invasion. We show that a heparan sulphate-specif ic monoclonal antibody specifically binds a glycosaminoglycan localized to the surface of the chlamydial organism and effectively neutralizes infectiv ity of both C. trachomatis and C. pneumoniae. In addition to the ability of this antibody to neutralize infectivity, direct visualization using immuno fluorescence demonstrated staining of chlamydial organisms localized to the intracellular vacuole. The chlamydial-associated glycosaminoglycan was spe cifically labelled with [C-14]-glucosamine, and the labelled compound was i mmunoprecipitated and resolved by gel electrophoresis. The chlamydial-assoc iated glycosaminoglycan is a high-molecular-weight compound similar in size to heparin or heparan sulphate and was sensitive to cleavage by heparan su lphate lyase. These data demonstrate that a glucosamine-containing sulphate d polysaccharide is produced within the intracellular vacuole containing ch lamydiae and is a target for antibody-mediated neutralization of infectivit y.