MEASUREMENT OF PNEUMOCOCCAL CAPSULAR POLYSACCHARIDE SEROTYPE-SPECIFICIMMUNOGLOBULIN-G IN HUMAN SERUM, A METHOD FOR ASSIGNING WEIGHT-BASED UNITS TO PROPOSED REFERENCE SERA

A direct method for measuring serotype-specific, class-specific antibo dy in proposed human reference sera is described. The assay uses a I-1 25-labeled, isotopically pure immunoglobulin G (IgG) as a primary stan dard in an antigen-antibody solid-phase enzyme immunoassay. From the m easurement of specific radioactivity bound to the adsorbed antigen, se rotype-specific IgG concentrations and optical density values can be d irectly related to optical density and serotype-specific IgG values fo r the reference Serum. We used this method to provisionally assign IgG concentrations in a pneumococcal reference serum to serotypes 1, 3, 6 A, 12F, 14,and 23F. This assay was found to be reproducible; the coeff icient of variation for duplicates was within 5%, and the day-to-day c oefficient of variation was from 3 to 18% for all six serotypes. The a ssay provides a general method for standardizing human reference serum pools with respect to concentration of antigen-specific IgM-, IgA-, a nd IgG-subclass antibodies.