Enzyme Linked Immunosorbent Assay (ELISA) for the detection of serum antibodies to the inner core lipopolysaccharide of Neisseria meningitidis Group B

Abstract

We have developed a solid-phase ELISA to study the human immune response to inner core lipopolysaccharide (LPS) of Neisseria meningitidis ( Nm) using structurally defined glycolipids from a genetically defined mutant ( galE) of a serogroup B Nm strain. Previous studies had demonstrated that a galE (inner core) LPS epitope is conserved in ∼70% Nm strains and was accessible to antibody in fully encapsulated wild-type Nm strains. A murine monoclonal antibody, MAb B5, raised to a galE mutant of serogroup B Nm strain, immunotype L3 (B.15.P1.7,16) was used to determine the specificity of the inner core LPS ELISA by inhibition studies using purified galE LPS and human sera. The intra-assay coefficient of variation (CV) was 5–6% and inter-assay CV was 19–22%. Using this ELISA, significant differences in the geometric mean titres (GMTs) of naturally occuring serum antibodies (specific to inner core LPS) between healthy adults (18–65 years, N=54) and healthy infants (3–4 months, N=144) of both IgG and IgM classes were found ( P<0.0001). GMTs were expressed in galE arbitrary units (AU/ml) (95% confidence intervals): IgG antibodies in adults 5.7 (5.0,6.9) and in infants 1.1 (1.0,1.3); IgM antibodies in adults 7.7 (5.7,10.4), and in infants 0.85 (0.7,1.1). In age-matched children aged 26–113 months a difference ( P=0.04) in specific IgG was found in healthy infants and infants in the acute phase of invasive Nm disease (GMT (95%CI) in AU/ml: in healthy infants 7.7 (5.3,11.0), in acute phase infants 4.2 (2.5,7.2). However, there was no difference in specific IgM ( P=0.98) between these groups healthy infants 4.7 (3.1,7.0), acute phase 4.6 (2.9, 7.4). In eleven children (5–181 months) there were differences in the GMTs of specific IgG and IgM ( P=0.02, P=0.008 respectively) between paired acute and convalescent sera (GMT) (95%CI) in AU/ml: IgG acute 1.95 (0.98, 3.8), convalescent 5.2 (2.2,12.4); IgM acute 1.78 (1.05,3.0), convalescent 4.38 (2.6,7.3). We conclude that ELISA is a specific, sensitive and reproducible method for the detection of antibodies to inner core LPS of Nm and that an epitope defined by MAb B5 can be immunogenic in infants and adults. These findings are relevant to the potential candidacy of inner core LPS as a vaccine.