Measurement of BK papovavirus IgG and IgM by radioimmunoassay (RIA)
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Current techniques for the measurement of BK papovavirus (BKV) specific IgM include sucrose density gradient centrifugation followed by hemagglutination inhibition (HAI) or indirect immunofluorescent (IF) staining of BKV infected cells using a fluorescein conjugated anti-human IgM antibody. These techniques are cumbersome and labor intensive and do not lend themselves to testing large numbers of sera. A solid phase radioimmunoassay (RIA) was developed to facilitate the measurement of BKV IgG and IgM in large numbers of sera. Solid phase antigen was prepared by adsorbing CsCl purified BKV antigen to polyvinyl chloride microtiter plates. Following reaction with serum, bound immunoglobulin was detected with iodinated goat anti-human IgG or IgM. RIA for the measurement of BKV IgG was sensitive with titers approaching 10(-6). Determination of IgG titers by RIA and HAI showed good agreement (P less than 0.01, correlation coefficient = 0.74). Measurement of BKV IgM was not affected by the presence of BKV IgG as evidenced by sucrose density gradient fractionation of IgM positive sera, removal of IgG by treatment with S. aureus protein A, and addition of BKV IgG to BKV IgM. Rheumatoid factor (RF) gave false positive IgM titers in the presence of BKV IgG when RF titers were greater than or equal to 1:640 by latex agglutination testing and BKV IgG levels exceed 1:256 by HAI. False positives due to RF could be eliminated by treatment of sera with sheep anti-human IgG antisera. RIA for BKV IgM was specific as sera containing JCV-, cytomegalovirus (CMV)-, rubella-, or hepatitis B core antibody (anti HBc)-IgM were negative by RIA. RIA detected BKV IgM in several sera from renal dialysis or allograft patients with titers ranging from 1:400 to 1:128,000 and demonstrated that BKV IgM persisted in sera of renal allograft patients for as long as 343 days post transplantation.
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