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Porin A (PorA), which determines the serosubtype of Neisseria meningitidis, is the main antigen of a candidate vaccine against serogroup B meningococci,which has been shown to induce high-avidity antibodies in children. We characterized the immune response of children after convalescing from meningococcal infection with a serosubtype P1.7-2,4 strain. Acute-and convalescent-phase sera of 21 c hildren with meningococcal septic shock caused by strains with PorA subtype P 1. 7-2,4 were collected. The serum bactericidal antibody titers, IgG isotype distr ibution, and antibody avidity were measured. We determined whether the differenc es in avidity of anti-outermembrane vesicle antibodies were PorA specific. Seru m bactericidal activity against H44/76 P 1.7-2,4 was < 4 in all convalescent sera. The IgG i sotype distribution of the convalescent sera was dominated by IgG1, followed by IgG3 , whereas no IgG2 or IgG4 was found. The geometric mean avidity index (GMAI ) of convalescent sera measured against a strain with the identical subtype as t he infective isolate was significantly higher than that against a strain with a heterologous PorA subtype or a PorA negative mutant strain (57 versus 35 and 23 %, respectively; p = 0.005 and p < 0.001). Geometric mean avidity titers were h ighest for P1.7-2,4, corresponding with the highest GMAI. The GMAI after invasi ve meningococcal disease was lower than after vaccination of healthy toddlers wi th a monovalent P1.7-2,4 outer membrane vesicle vaccine.
Porin A (PorA), which determines the serosubtype of Neisseria meningitidis, is the primary antigen of a candidate vaccine against serogroup B meningococci, which has been shown to induce high-avidity antibodies in children. We characterized the immune response of children after convalescing from meningococcal infection with a serosubtype P1.7-2,4 strain. Acute-and convalescent-phase sera of 21 c hildren with meningococcal septic shock caused by strains with PorA subtype P 1. 7-2,4 were collected. The serum bactericidal antibody We determined whether the differencies in avidity of anti-outer membrane folicle antibodies were PorA specific. convalescent sera. The IgG i sotype distribution of the convalescent sera was dominated by IgG1, followed by IgG3, no no IgG2 or IgG4 was found. The geometric mean avidity index (GMAI) of convalescent sera measur ed against a strain with the identical subtype as t he infective isolate was significantly higher than that against a strain with a heterologous PorA subtype or a PorA negative mutant strain (57 versus 35 and 23%, respectively; p = 0.005 and p <0.001) . Geometric mean avidity titers were h ighest for P1.7-2,4, corresponding with the highest GMAI. The GMAI after invasi ve meningococcal disease was lower than after vaccination of healthy toddlers wi th a monovalent P1.7-2,4 outer membrane vesicle vaccine.