Radioimmunoassay procedure for quantitating bacterial antibody in human sera

A RIA system was developed to detect antibodies in human sera against bacteria. Sonicates of Escherichia coli and Fusobacterium polymorphum were used as antigens to sensitize plastic-coated beads; antibodies to these antigens were detected with 125I-labelled antihuman globulin. Serum antibody titers against E. coli were determined by the serial dilution method; from the results, the standard curve principle was applied in determining the relative amounts of antibodies against E. coli in serum samples tested at a single dilution. The coefficient of variation of the RIA procedure was <10%. Serum titers obtained by the RIA and indirect immunofluorescence test were compared. RIA was more sensitive, quantitative and objective. Absorption studies using E. coli and F. polymorphum absorbents, indicated the specificity of the RIA system in detecting antibodies against E. coli and F. polymorphum. This RIA procedure offers a combination of desirable advantages; it is sensitive, objective, quantitative and easy to perform