The fimbrial antigens ofShigella flexneri

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Abstract
1. ‘Pure fimbrial antisera’ were prepared for Sh. flexneri strains of O-serotypes 1a, 2b, 3 and 4a and 5, by injecting rabbits with a living fimbriate-phase culture and absorbing the crude immune serum with a non-fimbriate-phase culture of the same strain to remove antibodies for the non-fimbrial (somatic) antigens. These sera gave at high titre a rapid, loosely floccular agglutination of all fimbriate-phase Flexneri cultures, caused adhesion of their fimbriae visible by electron-microscopy and inhibited their haemagglutinating activity. ‘Non-fimbrial antisera’, prepared by injection of non-fimbriate-phase cultures, were devoid of these activities; they gave somatic-type agglutination with fimbriate bacilli at lower titres than with homologous non-fimbriate bacilli, the fimbriae tending to mask the O-antigens and confer relative O-inagglutinability.2. Heating at 90°C. detached the fimbriae from the bacilli, so that these lost their haemagglutinating activity, fimbrial serum agglutinability and fimbrial agglutinin-binding power. When heated for 21/2 hr. at 100°C., the detached fimbriae retained agglutinin-binding power, but lost their immunogenicity.3. Cross-agglutination and absorption tests showed that the antigenic composition of the fimbriae was identical in all flexneri strains, irrespective of O-serotype. The flexneri pure fimbrial antisera agglutinated at low titre sixty out of sixty-six fimbriate Bact. coli strains. Absorption tests with a flexneri and three coli pure fimbrial antisera showed that the fimbriae of Sh. flexneri contained a major ‘flexneri-specific antigen’, found in only one coli strain, one or more minor ‘flexneri-coli antigens’ shared by a few coli strains. The coli fimbriae also contained a major, ‘coli type-specific antigen’ shared in groups of several related strains. The flexneri sera did not react with fimbriate strains of Bact. cloacae, Salmonella and Proteus.4. Fimbrial agglutinins for Sh. flexneri were found in eighty of eighty-one normal human sera at titres from 30 to 1920, and in some pre-immunization rabbit sera at titres of 30 to 60.