Human opsonins induced during meningococcal disease recognize outer membrane proteins PorA and PorB

Human opsonins directed against specific meningococcal outer membrane struc tures in sera obtained during meningococcal disease were quantified with a recently developed antigen-specific, opsonin-dependent phagocytosis and oxi dative burst assay. Outer membrane vesicles (OMVs) and PorA (class 1) and P orB (class 3) proteins purified from mutants of the same strain (44/76; B:1 5:P1.7.16) were adsorbed to fluorescent beads, opsonized with acute- and co nvalescent-phase sera from 40 patients with meningococcal disease, and expo sed to human leukocytes, Flow cytometric quantitation of the resulting leuk ocyte phagocytosis products (PPs) demonstrated that disease induced serum o psonins recognized meningococcal OMV components and both porins, The PPPorA and PPPorB values induced by convalescent-phase sera correlated positively with the PPOMV values. However, the PPPorB values were higher than the PPP orA values In convalescent-phase sera (medians [ranges] of 754 [17 to 1,057 ] and 107 [4 to 458], respectively) (P < 0.0001) and correlated positively with higher levels of immunoglobulin G against PorB than against PorA as ev aluated by enzyme linked immunosorbent assay. Extensive individual variatio ns in the anti-OMV and antiporin serum opsonic activities between patients infected by serotypes and serosubtypes homologous and heterologous to the t arget antigens were observed. Simultaneously measured oxidative burst activ ity correlated with the opsonophagocytosis, an indication that both of thes e important steps in the in vitro phagocytic elimination of meningococci ar e initiated by opsonins directed against OMV components, including PorA and PorB, In conclusion, human patient opsonins against meningococcal OMV comp onents and in particular PorB epitopes were Identified by this new method, which might facilitate selection of opsonin-inducing meningococcal antigens for inclusion in future vaccines.