In vitro neutralization of Chlamydia trachomatis with monoclonal antibody to an epitope on the major outer membrane protein.

A murine monoclonal antibody, which binds to an epitope on the major outer membrane protein of Chlamydia trachomatis and with species specificity in the micro-immunofluorescent assay, effectively neutralized in vitro two antigenically distinct serovars of C. trachomatis. Optimal concentrations of both organism and antibody were required to produce maximal neutralization of the organism. Neutralization was less effective and more variable at lower dilutions of antibody than at higher dilutions, suggesting a prozone phenomenon. A radiolabeled attachment assay demonstrated that attachment of elementary bodies was unaffected by earlier treatment with antibody and that neutralization occurred at a step after attachment. The epitope to which this antibody is directed, on the major outer membrane protein of C. trachomatis, may have an important role in determining infectivity of the organism.