Assessment of immune response to meningococcal disease: comparison of a whole-blood assay and the serum bactericidal assay

A whole-blood assay (WBA), which assesses the complete bactericidal activit y of blood, was compared with the serum bactericidal assay (SBA), which mea sures antibody and complement mediated cell lysis. Twenty children infected with serogroup B strains and 25 infected with serogroup C strains were stu died 8-12 weeks after disease, and 29 healthy children were used as control s. The infecting strain (convalescent children only) and two reference stra ins, MC58 (B:15:P1.7, 16) and NCTC 8554 (C:NT:P1.5) were used. In children previously infected with a serogroup B strain, bactericidal activity was de tected in 95% and 85% to their infecting strain by the WBA (>50% killing) a nd the SEA (greater than or equal to 4), respectively. Bactericidal activit y to the reference serogroup B and C strain was detected by WBA in 70 and 7 5% of children, respectively, and the SEA in 45% and 20%. In contrast bacte ricidal activity was detected to both serogroup C strains in >80% of childr en previously infected with a serogroup C strain using either assay and in 48% (WBA) and 20% (SBA) to the reference serogroup B strain. Levels of bact ericidal activity were detectable in fewer control children. Children conva lescing from meningococcal disease develop an immune response to their infe cting strain, detectable by both the WBA and SEA, which is independent of a ge. However, the WBA appears to be a more sensitive measure of bactericidal activity to heterologous strains than the SEA.