IGG SUBCLASS ANTIBODIES TO HUMAN CYTOMEGALOVIRUS (CMV) IN NORMAL HUMAN PLASMA SAMPLES AND IMMUNE GLOBULINS AND THEIR NEUTRALIZING ACTIVITIES

An enzyme-linked immunoabsorbent assay (ELISA) was developed for quant itation of IgG subclass antibodies to human cytomegalovirus (CMV) in h uman serum or plasma samples and in immune globulin (IG) preparations. The assay was based on the parallel titration of known concentrations of purified IgG subclass myeloma proteins and a specific CMV antiseru m. The purified IgG subclass myeloma proteins were captured on an ELIS A plate pre-coated with anti-human kappa, anti-human lambda or a mixtu re of anti-human kappa and lambda antibodies and the specific antiseru m was titrated against CMV antigen coated on the plate. IgG subclass a ntibodies, captured or bound to antigen, were quantitated with IGG sub class heavy chain specific monoclonal antibodies. The method was highl y reproducible, specific and sensitive. Using this method, 257 human p lasma samples and 50 IG preparations were assayed for CMV specific IgG subclass and IgM antibodies. The major IgG subclass antibody to CMV w as IgG1 which represented more than 96% of CMV IgG antibodies, followe d by IgG3 (mean CMV IgG3 antibody content was 3% of IgG antibodies in IG preparations and 18% in plasma samples). A majority of the samples had low levels of IgG2 antibodies and a few samples exhibited low leve ls of lgG4 antibodies. IG preparations showed very low levels of CMV I gM antibodies whereas plasma samples had 14.2% of CMV antibodies (IgG and IgM) as IgM antibodies. Virus neutralizing (Nt) activity of these samples showed a significant correlation with CMV IgG1 antibodies. Nin e samples of plasma and IGs were further evaluated for Nt activity of IgG1 and IgG3 antibodies by separating IgG3 from the rest of the antib odies with protein A agarose. IgG3 antibodies showed much higher Nt ac tivity than IgG1 antibodies suggesting that enrichment of IgG3 antibod ies in IG preparations may be useful in preparing CMV specific IG. (C) 1996 The International Association of Biological Standardization