STANDARDIZATION AND A MULTILABORATORY COMPARISON OF NEISSERIA-MENINGITIDIS SEROGROUP-A AND SEROGROUP-C SERUM BACTERICIDAL ASSAYS

A standardized serum bactericidal assay (SEA) is required to evaluate the functional activity of antibody produced in response to Neisseria meningitidis serogroup A and C vaccines. We evaluated assay parameters (assay buffer, target strains, growth of target cells, target cell nu mber, complement source and concentration, and methods for growth of s urviving bacteria) which may affect the reproducibility of SEA titers. The various assay parameters and specificity of anticapsular antibody to five serogroup A strains (A1, ATCC 13077, F8238, F9205, and F7485) and four serogroup C strains (C11, G7880, G8050, and 1002-90) were ev aluated with Centers for Disease Control and Prevention meningococcal quality control sera. The critical assay parameters for the reproducib le measurement of SEA titers were found to include the target strain, assay incubation time, and complement. The resulting standardized SEA was used by 10 laboratories to measure functional anticapsular antibod y against serogroup A strain F8238 and serogroup C strain C11. In the multilaboratory study, SBA titers were measured in duplicate for 14 pa irs of sera (seven adults and seven children) before and after immuniz ation with a quadrivalent polysaccharide (A C, Y, and W-135) vaccine. The standardized SEA was reliable in all laboratories regardless of ex perience in performing SBAs. For most sera, intralaboratory reproducib ility was +/-1 dilution; interlaboratory reproducibility was +/-2 dilu tions. The correlation between median titers (interlaboratory) and enz yme-linked immunosorbent assay total antibody concentrations was high for both serogroup A (r = 0.86; P < 0.001; slope 0.5) and serogroup C (n = 0.86; P < 0.001; slope = 0.7). The specified assay, which include s the critical parameters of target strain, incubation time, and compl ement source, will facilitate interlaboratory comparisons of the funct ional antibody produced in response to current or developing serogroup A and C meningococcal vaccines.