Multiplexed immunoassay to assess Shigella-specific antibody responses

Infection with Shigella spp. results in bacillary dysentery and a systemic and mucosal antibody response. The immune response is directed at multiple antigens, including LPS and the invasin plasmid antigen (Ipa) proteins, and is capable of conferring short-term, serotype-specific protection. Both live-attenuated and several subunit vaccine approaches have focused on inducing a pronounced mucosal immune response directed to the same antigens recognized after natural infection. Traditionally, Shigella-specific antibody responses are measured using ELISA. Although ELISAs are robust immunological assays, limited sample volume and assay costs often precludes its use for immunological evaluation against multiple antigens. To overcome these shortcomings, a novel assay has been developed to simultaneously measure specific antibody levels to six Shigella antigens, including three serotype-specific LPS preparations and three conserved protein antigens in a Luminex™-based system. Coupling methods were optimized to covalently link recombinant Ipa proteins (IpaB, IpaC, and IpaD) and purified LPS from Shigella sonnei, Shigella flexneri 2a, and Shigella dysenteriae 1 to unique bead sets. The antigen-coupled beads maintained stable reactivity with monoclonal antibodies (mAbs) for 6 weeks (protein) to 3 months (LPS). The specificity of the Luminex assay was similar to an ELISA, with the multiplexed assay providing a larger dynamic range. Comparable levels of antigen-specific reactivity were attained in monoplex or multiplex formats indicating limited interference. The correlations (R(2)) between the ELISA and the multiplexed assay along with the repeatability and reproducibility of the assay were very high. Minor changes in species-specific conjugated secondary antibodies allowed the optimized multiplexed assays to be used to assess antigen-specific antibodies in serum or blood eluted from filter paper isolated from mice and guinea pigs highlighting applicability of the assay for seroepidemiology and pre-clinical/clinical vaccine studies.