BORDETELLA-PERTUSSIS FIMBRIAE BIND TO HUMAN MONOCYTES VIA THE MINOR FIMBRIAL SUBUNIT FIMD

Nonopsonized Bordetella pertussis can bind to and become ingested by h uman monocytes. Previous studies demonstrated that mutant B. pertussis strains that lack fimbriae express a reduced adherence to monocytes. The present study was undertaken to investigate the involvement of the minor fimbrial subunit FimD in the adherence of B. pertussis to human monocytes using purified fimbriae, FimD, and strains with mutations i n fimbrial genes. Flow cytometry demonstrated that purified B. pertuss is fimbriae avidly bind to monocytes in a dose-dependent manner but bi nd less to neutrophils and hardly to lymphocytes; FimD-lacking fimbria e did not bind to monocytes. Purified fimbriae or FimD inhibited the b inding of wild-type B. pertussis to monocytes in a dose-dependent mann er and similarly inhibited the binding of a mutant defective in the ma jor fimbrial subunits. It did not affect the binding of strains defect ive in FimD. These results prove that B. pertussis bind to human monoc ytes via the fimbrial minor subunit FimD.