Enzyme linked immunosorbent assay (ELISA) for the detection of serum antibodies to the inner core lipopolysaccharide of Neisseria meningitidis group B

We have developed a solid-phase ELISA to study the human immune response to inner core lipopolysaccharide (LPS) of Neisseria meningitidis (Nm) using s tructurally defined glycolipids from a genetically defined mutant (galE) of a serogroup B Nm strain. Previous studies had demonstrated that a galE (in ner core) LPS epitope is conserved in similar to 70% Nm strains and was acc essible to antibody in fully encapsulated wild-type Nm strains. A murine mo noclonal 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 hum an sera. The intra-assay coefficient of variation (CV) was 5-6% and inter-a ssay CV was 19-22%. Using this ELISA, significant differences in the geomet ric mean titres (GMTs) of naturally occuring serum antibodies (specific to inner core LPS) between healthy adults (18-65 years, N=54) and healthy infa nts (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 interva ls): Ige antibodies in adults 5.7 (5.0,6.9) and in infants 1.1 (1.0,1.3); I gM antibodies in adults 7.7 (5.7,10.4); and in infants 0.85 (0.7,1.1). In a ge-matched children aged 26-113 months a difference (P=0.04) in specific Ig G was found in healthy infants and infants in the acute phase of invasive N m disease (GMT (95%CI) in AU/ml: in healthy infants 7.7 (5.3,11.0), in acut e 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 pha se 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), conval escent 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 ad ults. These findings are relevant to the potential candidacy of inner core LPS as a vaccine. (C) 2000) Elsevier Science B.V. All rights reserved.