Protective capacity of antibodies against Escherichia coli and K antigens.

Antibodies to Escherichia coli O and K antigens were raised in rabbits by repeated immunizations with whole, Formalin-killed and, later, liver bacteria. The serum antibody levels were determined with the ammonium sulfate precipitation technique after radioiodinating the antigens. The K antigens had to be conjugated to proteins before labeling. Such conjugations were performed using cyanogen bromide for the K1 antigen and bisdiazobenzidine for the K13 antigen. The protective capacities of the rabbit antisera were tested in intraperitoneally infected mice. The protective capacity of the antisera was expressed per ammonium sulfate precipitation titer. The results showed a significantly higher protective effect for the antibodies against the K1 and K13 antigens than for the antibodies against the O2 and O6 lipopolysaccharides.