A multiplexed fluorescent microsphere immunoassay for antibodies to pneumococcal capsular polysaccharides.

We developed a multiplexed indirect immunofluorescent assay for antibodies to pneumococcal polysaccharides (PnPs) based on the Luminex multiple analyte profiling system (Luminex, Austin, TX). The assay simultaneously determines serum IgG concentrations to 14 PnPs serotypes: 1, 3, 4, 5, 6B, 7F, 8, 9N, 9V, 12F; 14, 18C, 19F, and 23F. To assess the specificity of the multiplexed assay for each individual serotype, inhibition-of-binding studies were conducted using adult serum samples obtained after pneumococcal vaccination. Except for the closely related serotypes 9V and 9N, we demonstrated inhibition by homologous serotypes of more than 95% and inhibition by heterologous serotypes of less than 15% for all 14 PnPs serotypes. There was, however, high heterologous inhibition of 50% or greater with some serotypes. These cross-reacting antibodies could not be removed by preabsorption with pneumococcal C-polysaccharide but were removed by additional preabsorption with serotype 22F polysaccharide. The multiplexed Luminex assay showed good overall agreement with a well-established enzyme-linked immunosorbent assay that is currently recommended for evaluation of pneumococcal vaccine immunogenicity.