False RIA IgM titres to herpes simplex virus and cytomegalovirus: factors causing them, and their absorption by protein A-Sepharose/IgG-protein A-Sepharose.

A method for the absorption of false radioimmunoassay (RIA) IgM titres against herpes simplex virus (HSV) and cytomegalovirus (CMV) is presented. The serum specimens were absorbed by a mixture of protein A-Sepharose and protein A-Sepharose saturated with normal human gamma globulin (PAS/IgG). The detection of rheumatoid factor of IgM class (IgM-RF) as well as antinuclear antibodies (ANA) of both IgM and IgG class by solid-phase RIA is also described, and their role in the false IgM results was studied. It was found that the PAS/IgG absorption removed 50-90% of both IgM-RF and total IgG. The reduction of IgM-ANA clustered at 50-90% or nothing, whereas the reduction of IgG-ANA was approximately 50%. The studies with HSV and CMV antigens indicated that the removal of false IgM titres was more effective than the removal of each of these four factors. It was concluded that the IgM-RF titres alone were not sufficiently high to explain the false IgM results, but the ANA activity probably contributed.