SHIFT IN S-LAYER PROTEIN EXPRESSION RESPONSIBLE FOR ANTIGENIC VARIATION IN CAMPYLOBACTER-FETUS

Campylobacter fetus strains possess regular paracrystalline surface la yers (S-layers) composed of high-molecular-weight proteins and can cha nge the size and crystalline structure of the predominant protein expr essed. Polyclonal antisera demonstrate antigenic cross-reactivity amon g these proteins but suggest differences in epitopes. Monoclonal antib odies to the 97-kDa S-layer protein of Campylobacter fetus subsp. fetu s strain 82-40LP showed three different reactivities. Monoclonal antib ody 1D1 recognized 97-kDa S-layer proteins from all C fetus strains st udied; reactivity of monoclonal antibody 6E4 was similar except for ep itopes in S-layer proteins from reptile strains and strains with type B lipopolysaccharide. Monoclonal antibody 2E11 only recognized epitope s on S-layer proteins from strains with type A lipopolysaccharide rega rdless of size. In vitro shift from a 97-kDa S-layer protein to a 127- kDa S-layer protein resulted in different reactivity, indicating that size change was accompanied by antigenic variation. To examine in vivo variation, heifers were genitally challenged with Campylobacter fetus subsp. venerealis strains and the S-layer proteins from sequential is olates were characterized. Analysis with monoclonal antibodies showed that antigenic reactivities of the S-layer proteins were varied, indic ating that these proteins represent a system for antigenic variation.