Enzyme-linked protein A: an enzyme-linked immunosorbent assay reagent for detection of human immunoglobulin G and virus-specific antibody.

A general-purpose reagent capable of reacting with immunoglobulin G in a modified enzyme-linked immunosorbent assay technique was prepared by using protein A coupled with horseradish peroxidase. The reagent detected low levels (0.003 to 1.0 microgram/ml) of human immunoglobulin G and was also applied in an enzyme-linked immunosorbent assay for titration of antibody to human cytomegalovirus. The antibody titers to human cytomegalovirus determined by enzyme-linked immunosorbent assay and by complement fixation were compared. The correlation coefficient between the two techniques was 0.85, but the enzyme-linked immunosorbent assay was 10 times more sensitive than complement fixation in terms of antibody titers detected.