Neutralization of Chlamydia trachomatis: kinetics and stoichiometry.

Monoclonal antibodies to the major outer membrane protein of Chlamydia trachomatis were used to neutralize C. trachomatis infectivity in HeLa 229 cells and to determine the kinetics and stoichiometry of the reaction. In vitro neutralization of C. trachomatis infectivity proceeded as a first-order reaction and required an activation energy of approximately 20 kcal/mol (ca. 84 kJ/mol). The rate of neutralization was linear with respect to antibody concentration and reaction temperature. The efficiency of neutralization decreased exponentially as the ratio of noninfective to infective chlamydiae increased in the antigen preparation. The neutralization assay was also significantly affected by reaction parameters such as the reaction volume and the duration of incubation. Stoichiometric calculations showed that an average ratio of 10(3) and 10(4) immunoglobulin molecules per chlamydial particle was required to yield 50% neutralization by monoclonal antibodies specifying serovar-specific and species-specific epitopes, respectively. The implications of these findings for vaccine design and for the role of the major outer membrane protein in the pathogenesis of chlamydial infections are discussed.