Abstract
Purified protein A (PA) from Staphylococcus aureus was conjugated with the enzyme alkaline phosphatase. This reagent reacted well with pig, rabbit and guinea pig IgG and less well with mouse and bovine IgG. Radioactive 125I-labelled PA showed a similar affinity for the IgGs examined. Antibodies against foot-and-mouth disease virus contained in guinea pig, rabbit and pig serum were detected, using the enzyme-conjugated PA in indirect tests, which were of similar sensitivity to those using enzyme-conjugated anti-species antibody as tracer.