Detection of cytomegalovirus by ELISA in urine samples is inhibited by β2 microglobulin

AbstractDuring development of an enzyme immunoassay for the detection of cytomegalovirus (CMV) we previously discovered that virus found naturally in urine specimens could not be captured onto the solid phase by CMV‐specific monoclonal antibodies, whereas these same antibodies could capture CMV from cell culture supernatants. We now report that urine from normal CMV‐seronegative individuals contains a substance of molecular weight 11–12,000 daltons that inhibits the ELISA detection of cell culture‐grown CMV. The addition of a known urinary protein of this molecular weight, β2 microglobulin (βm; 11,700 daltons), inhibited the detection of cell culture‐grown CMV in the ELISA over the concentration range found in clinical urine samples. In contrast, another low molecular weight urinary protein, lysozyme, had no inhibitory effect. β2m caused inhibition only when added to the virus preparation and not to the antibody‐capture stage. We conclude that β2m in urine prevents the detection of CMV by ELISA by binding to the virus and masking its antigenic determinants and we culculate that of the order of 105 molecules of β2m bind to each particle of cell culture‐grown CMV. We postulate that CMV in fresh urine specimens is similarly coated with β2m, accounting for the failure to detect it by ELISA.