A simple, quantitative, reproducible avidin-biotin ELISA for the evaluation of group B Streptococcus type-specific antibodies in humans

Type-specific antibodies to the capsular polysaccharides (CP) of group B Streptococcus (GBS) are protective Historically, the radioactive antigen-binding assay (RABA) has been used to determine GBS antibody levels. This method measures total immunoglobulin and employs the use of radioactive materials. We have developed an avidin-biotin ELISA that is less hazardous and is able to measure GBS la, Ib, II or III CP specific IgG, To avoid inconsistent binding to the plate, the CPs from GBS In, Ib, II and III were derivatized using adipic acid dihydpazide (ADH) and subsequently biotinylated without altering their antigenic epitopes and bound to avidin coated plates. Plasma from three different human subjects immunized with a tetravalent CP vaccine were used to prepare IgG references for Ia, II and III, respectively, thus rendering the assay quantitative for those types. The assay is able to detect nanograms per milliliter of GBS Ia, Ib, II or III specific antibody. This method is reproducible, sensitive and correlates with RABA by 76%. Copyright (C) 1996 Elsevier Science Ltd.