LOCALIZATION AND IMMUNOLOGICAL PROPERTIES OF A 24-KDA SURFACE PROTEINOF HAEMOPHILUS-DUCREYI

The cell wall and outer structures of Haemophilus ducreyi bacteria wer e investigated. The 24-kDa outer protein from two strains was purified with an SDS-PAGE preparative continuous-elution electrophoresis cell. The protein was further characterised by SDS-PAGE and immunoblotting, and the immunological properties were investigated by ELISA. Localisa tion on the bacterial surface was investigated by immune-electronmicro scopy with a polyclonal antiserum raised against the purified protein. A triple-laminar cell wail typical of gram-negative bacteria, close c ellular contact between bacterial cells and outer blebs were seen on t hin sections. An additional high mel. wt band of c. 165 kDa was seen w hen not treated by heating to 100 degrees C. A high density fibrilla-l ike material was detected on the bacterial cell and in the environment by negative staining and immune-electronmicroscopy with antisera spec ific for the 24-kDa protein. The surface localisation of the 24-kDa pr otein was confirmed by an ELISA technique with the specific antiserum and whole bacterial cells as antigen. The presence of antibodies to th e 24-kDa protein was demonstrated in antisera to 13 strains of H. ducr eyi, indicating antigenic identity or within-species crossreactivity. Low titres of antibodies to this protein were also detected in 19 anti sera raised against different strains of gram-negative bacteria, indic ating cross-reactivity with other species. Antibody response to the 24 -kDa protein in rabbits immunised subcutaneously with live bacteria re sulted in a secondary IgG response. Of 28 sera from patients with cult ure-verified chancroid, 26 manifested high titres of IgG antibodies to the 24-kDa protein, thus indicating the involvement of this antigen i n the disease process in man.