Quantification of cell-associated and free antigens in Bordetella pertussis suspensions by antigen binding ELISA

In order to achieve batch-to-batch consistency of whole-cell pertussis vaccines, properties relevant for protection and safety should be characterised. Therefore, ELISAs to quantify pertussis toxin (PT), filamentous haemagglutinin (FHA), 92 kD outer membrane protein (92 kD-OMP) and pertactin (PRN) in Bordetella pertussis (B. pertussis) suspensions were developed. In this paper the influence of the bacterial growth stage on antigen production and antigen release into the supernatant was studied for pertussis strains 134, 509 and CS. The levels of cell-associated and free antigens during growth were strongly strain and antigen dependent. Because of this, the proportion of cell-associated antigens changed during cultivation for all three strains. Substantial amounts of PT and PRN were released into the supernatant, while little free FHA and 92 kD-OMP were found. The amount of cell-associated FHA declined rapidly during growth, whereas cell-associated 92 kD-OMP contents increased. These findings demonstrate that, although antigen exposure and release differ from strain to strain, the main factor that determines the antigen production and release is the growth phase.