Importance of Complement Source in Measuring Meningococcal Bactericidal Titers

Abstract

Complement-mediated bactericidal antibodies in serum confer protection against meningococcal disease. The minimum protective titer is estimated to be between 1:4 and 1:8 when measured by the Goldschneider assay performed with human complement, the assay used in the 1960s to establish the correlation between bactericidal antibodies and protection. A more recently described bactericidal assay standardized by an international consortium uses rabbit complement, which is known to augment bactericidal titers. To define a protective titer measured by the standardized assay, we compared bactericidal titers against serogroup C strains measured by this assay to titers measured by the assay described by Goldschneider et al. A titer of >1:128 measured by the standardized assay was needed to predict with >80% certainty a positive titer of >1:4 as measured by the Goldschneider assay. However, the majority of samples with titers of 1:4 measured by the Goldschneider assay had titers of <1:128 when measured by the standardized assay. Therefore, by the results of the standardized assay such persons would be falsely categorized as being susceptible to disease. In conclusion, high bactericidal titers measured with the standardized assay performed with rabbit complement are predictive of protection, but no threshold titer is both sensitive and specific for predicting a positive titer measured by the Goldschneider assay using human complement. Up to 10% of the U.S. adult population lacks intrinsic bactericidal activity against serogroup C strains in serum and can serve as complement donors. Therefore, use of the Goldschneider assay or an equivalent assay performed with human complement is preferred over assays that use rabbit complement.

Persistence of immune responses after a single dose of Novartis meningococcal serogroup A, C, W-135 and Y CRM-197 conjugate vaccine (Menveo®) or Menactra® among healthy adolescents

“…12 Previous studies have found a lack of correlation between hSBA and rSBA results; 12 however, our data did not detect any instances where the rSBA results contradicted the hSBA results. For serogroups A, W-135 and Y, MenACWY-CRM recipients were significantly more likely than MCV4 recipients to have evidence of bactericidal antibodies almost 2 years after vaccination, regardless of the complement source used, while the proportions of subjects achieving rSBA or hSBA titers ≥8 were similar for serogroup C in recipients of both vaccines.…”

Oral administration of recombinantNeisseria meningitidisPorA genetically fused toH. pyloriHpaA antigen increases antibody levels in mouse serum, suggesting that PorA behaves as a putative adjuvant

“…34,51,66 The titers of bactericidal activity were between 1:8 and 1:16, surpassing the accepted values for protective bactericidal activity titers in Europe ( 1:4) and in the US ( 1:8). 67 In summary, these data support the use of rPorA as an adjuvant and in the development of a novel meningococcal B oral vaccine. The next-generation vaccine NonaMen induced high SBA titers against all tested MenB strains, when administered subcutaneously in rabbits and mice, regardless of whether aluminum phosphate was used as an adjuvant, 31 suggesting that an adjuvant was not necessary.…”

Naturally Acquired Passive Protective Activity against Neisseria meningitidis Group C in the Absence of Serum Bactericidal Activity

“…Serum bactericidal activity also was measured with internal human complement, which was used in the Goldschneider et al study (10), or exogenous rabbit complement, which because of ease of standardization is currently used by most laboratories to measure bactericidal titers (1, 3) but is known to give higher bactericidal titers than human complement (3,32). Irrespective of the source of complement used, protective activity was more frequently found in sera that were positive for bactericidal activity (with a titer of Ն1:4 with human complement or Ն1:128 with rabbit complement) than in sera that were negative for bactericidal activity (P Ͻ 0.001).…”

“…For log transformation, samples below the lower limits of detection were assigned a value of half of the lower limit (i.e., 1:2 for the bactericidal titer and 0.05 g/ml for group C anticapsular antibody concentration measured by RABA). The proportion of sera with bactericidal titers of Ն1:4 (considered a protective titer [10]) or Ն1:128 when measured with rabbit complement (a titer previously shown to predict a bactericidal titer of Ն1:4 when measured with human complement [32]) was computed. Differences found in the proportion of subjects in the respective groups were compared by chi-square analysis.…”

“…There is a strong scientific basis for inferring meningococcal vaccine efficacy from immunogenicity data (3,10,11). However, the choice of in vitro assay conditions and serologic endpoints for inferring protection against meningococcal disease are topics of considerable recent debate (1,3,16,32). The reasons are complex but ultimately have to do with the effects of potential disparities between in vitro antibody functional assay conditions and in vivo host defenses.…”