A new flow-cytometry-based opsonophagocytosis assay for the rapid measurement of functional antibody levels against Group B Streptococcus

Analysis of sera from mice immunized with different GBS vaccines revealed comparable sensitivity and specificity with the traditional killing OPA assay (kOPA), and a good correlation between the fluorescent signal of bacteria internalized by HL-60 phagocytes and killing. Remarkably, the pHrodo-based approach reduced the variability observed with other fOPA assays. The obtained data indicate the proposed fOPA as a reliable and useful tool for functional antibody assessment.