Serum opsonic and bactericidal activity after Neisseria meningitidis group A + C and Haemophilus influenzae type b vaccination: a comparison of three functional assays

Abstract

Three functional assays on immunity, serum bactericidal activity (SBA), phagocytic killing (PK) and an index calculation of chemiluminescence induced in polymorphonuclear leukocytes (CL-index), were compared with an enzyme linked immunoassay (ELISA) of the concentration of the total Ig-fraction of anticapsular antibodies in 28 healthy adults immunized against Haemophilus influenzae type b (Hib) or Neisseria meningitidis serogroup A and C (Me A + C). The immunization evoked a serum response measurable with all assays and a high concentration of antibodies against McA, McC and Hib usually was associated with functional activity and vice versa. However, qualitative differences were found and five of the vaccines (18%) were non-responders in functional assays despite a significant seroconversion measured by ELISA. A functional test may prove valuable in bacterial vaccine trials as complementary to immunochemical calculations of anticapsular antibodies. For estimates of opsonic activity bactericidal serum activity interferes in the PK assay, which is demonstrated in the present study. As an alternative, the CL assay, with the index technique described, is a reliable, less laborious and effective test on opsonophagocytosis.