Monoclonal antibody neutralization of unmanipulated Chlamydia trachomatis serovar A infection of human epithelioid cells (A-431)

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Abstract
A human epithelioid cell line (A-431) was tested in parallel with McCoy fibroblast cells for the growth of trachoma-related serovar A Chlamydia trachomatis without centrifugation or cycloheximide addition. A-431 cells were 4–7 times more susceptible to infection with serovar A than McCoy cells in such unmanipulated cultures. Murine monoclonal antibodies (MAbs) developed against serovar A were then evaluated for their ability to inhibit unmanipulated serovar A infectivity of A-431 cells. Two of seven MAbs tested neutralized infectivity by more than 50%. An IgG2a MAb (2C8) that is specific for serovar A, and another IgG2a MAb (4E3) that reacts equally with serovars A and L2 neutralized infectivity of serovar A by 72.2 ± 3.7% and 56.0 ± 5.8% (mean ± SEM of 7 experiments) respectively. Mouse immune serum (MIS) raised against serovar A elementary bodies (EB) neutralized infectivity of serovar A by 76.0 ± 4.9% (mean ± SEM of 7 experiments). Immunoblot detection of serovar A EB polypeptides separated by SDS-PAGE indicated that 2C8 reacted with a 16 kD and 4E3 reacted with a 12 kD polypeptide while MIS reacted with several polypeptides including the major outer membrane protein (MOMP). These studies show that the human epithelioid cell line A-431 is a more susceptible host than McCoy cells in unmanipulated cultures, and that 2 MAbs neutralize serovar A infectivity of A-431 cells. Identification of antigenic moieties of importance in unmanipulated chlamydial infections may help in the development of potential vaccines against trachoma.