Specificity of Subcapsular Antibody Responses in Ethiopian Patients following Disease Caused by Serogroup A Meningococci

Abstract

Dissecting the specificities of human antibody responses following disease caused by serogroup A meningococci may be important for the development of improved vaccines. We performed a study of Ethiopian patients during outbreaks in 2002 and 2003. Sera were obtained from 71 patients with meningitis caused by bacteria of sequence type 7, as confirmed by PCR or culture, and from 113 Ethiopian controls. Antibody specificities were analyzed by immunoblotting (IB) against outer membrane antigen extracts of a reference strain and of the patients' own isolates and by enzyme-linked immunosorbent assay for immunoglobulin G (IgG) levels against lipooligosaccharide (LOS) L11 and the proteins NadA and NspA. IB revealed that the main antigens targeted were the proteins PorA, PorB, RmpM, and Opa/OpcA, as well as LOS. MenA disease induced significant increases in IgG against LOS L11 and NadA. The IgG levels against LOS remained elevated following disease, whereas the IgG anti-NadA levels returned to acute-phase levels in the late convalescent phase. Among adults, the anti-LOS IgG levels were similar in acute-phase patient sera as in control sera, whereas anti-NadA IgG levels were significantly higher in acute-phase sera than in controls. The IgG antibody levels against LOS and NadA correlated moderately but significantly with serum bactericidal activity against MenA strains. Future studies on immune response during MenA disease should take into account the high levels of anti-MenA polysaccharide IgG commonly found in the population and seek to clarify the role of antibodies against subcapsular antigens in protection against MenA disease.

A Seroepidemiological Study of Serogroup A Meningococcal Infection in the African Meningitis Belt

“…Although a number of studies of meningococcal serology have been performed previously in countries of the African meningitis belt, most of these have been undertaken in the context of evaluation of the response to vaccination[ 7 – 10 ] or in disease survivors. [ 19 ] Comparisons between the results obtained in individual studies can be difficult when standardised methods are not used. Therefore, for this comparative study, substantial efforts were made to standardise the ELISA technique used at each of the collaborating centres with support from the Vaccine Evaluation Unit at PHE, Manchester, UK.…”

Characterization of an Antibody Depletion Assay for Analysis of Bactericidal Antibody Specificity

“…In addition, a relatively large amount of serum is required, and the chemical bonding of the antigen to the matrix may alter important antigen epitopes. The depletion assay does not require denaturation of the antigen by hot detergent prior to resolution on a polyacrylamide gel, as required for Western blot analysis (11,21). Since bactericidal antibodies may bind preferentially to conformational determinants on outer membrane proteins, some bactericidal antibodies may not bind on a Western blot.…”

“…Various approaches have been used to obtain specificity information, including the use of different bactericidal test strains that differ in known ways from each other, the use of genetically engineered test strains (3,19), correlation of results of Western blotting with bactericidal activity (11,21), and inhibition of bactericidal activity by addition of soluble antigen at various concentrations to the bactericidal assay mixture (12,15). All of these approaches have limitations and potential problems.…”

An Outer Membrane Vesicle Vaccine for Prevention of Serogroup A and W‐135 Meningococcal Disease in the African Meningitis Belt

“…A substantial part of the serum antibodies in normal individuals with bactericidal activities against meningococci is shown to be directed against non‐capsular antigens [17–19]. Meningococcal outer membrane proteins may, therefore, serve as alternative vaccine antigens to the capsular polysaccharides.…”