Binding properties and anti-bacterial activities of V-region identical, human IgG and IgM antibodies, against group B Neisseria meningitidis

Abstract

We have constructed chimaeric (ch) mouse/human antibodies with identical binding regions isolated from the V-genes of two mouse parent hybridoma cell lines, with specificity against the P1.7 and P1.16 epitopes on the outer-membrane protein PorA on meningococci. The chimaeric antibodies can be used to analyse relationships between specificity, binding activity (avidity and kinetics), isotype (antibody class and antibody subclass) and in vitro anti-bacterial activity of meningococcal antibodies. The antibody sets represented the human isotypes IgG1, IgG3 and IgM, which dominate during immune response against protein antigens. The binding activities were quite similar for all these isotypes, surprisingly also for the pentameric IgM. Interestingly, monomeric IgM, prepared from pentameric IgM by partially reduction and alkylation, had similar binding activities as the original pentameric IgM. Regarding in vitro anti-bacterial activity, chIgG1 was superior in SBA (serum bactericidal activity) compared with chIgG3, while chIgG3 was more efficient in OP (opsonophagocytosis; measured by flow cytometry) than chIgG1. ChIgM showed slightly higher SBA than chIgG1 on molar basis, and much higher OP than chIgG3 and chIgG1. A lower concentration of antibodies was needed against the P1.16 than against the P1.7 epitope to induce SBA, but this was not the case for OP.

Protection by Natural Human Immunoglobulin M Antibody to Meningococcal Serogroup B Capsular Polysaccharide in the Infant Rat Protection Assay Is Independent of Complement-Mediated Bacterial Lysis

“…At low complement concentrations (Ͻ10%) activation of complement occurs mainly through the classical pathway (59). However, previous studies comparing monoclonal IgG and IgM antibodies against meningococcal surface PorA protein revealed IgM to be more active than IgG in OPA under conditions similar to those used in the present study (29,30). Also, when different concentrations of complement serum were tested with a human monoclonal IgM anti-P1.…”

A Systematic Comparison of Free and Bound Antibodies Reveals Binding-Related Conformational Changes

“…Thus, a conformational change in this loop may affect the relative orientation of the CH1 domain versus the Fc, thereby influencing effector binding to the Fc. There are now many examples of Abs with identical variable domains but different isotypes that bind the same Ag with a different affinity or specificity (13,(15)(16)(17)(18)(19)(20)(21)(22)(23)(24). Some of these studies suggested that the CH1 domain accounts for the observed changes in binding, because it was identified as the only region with sequence diversity between the tested Abs and because a similar effect was observed using only the Fab instead of the entire Ab scaffold (13,16,19).…”

“…However, recent reports provide some evidence for binding-related allosteric effects in Abs. It was demonstrated that Ag binding, as well as the structure of the variable domains, may be influenced by changes in the constant domains (11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22)(23)(24). For example, Pritsch et al (13) demonstrated that two human mAbs sharing identical variable domains, but expressing different isotypes, bind tubulin with significantly different affinities.…”

Combined Roles of Human IgG Subclass, Alternative Complement Pathway Activation, and Epitope Density in the Bactericidal Activity of Antibodies to Meningococcal Factor H Binding Protein

“…In one study, all three IgG1 anti-PorA MAbs tested had superior bactericidal activity to the respective IgG3 MAbs (28), while in the second study an IgG1 anti-PorA MAb had similar or better activity than the IgG3 MAb (37). The second study also investigated the activity of a chimeric IgG2 anti-PorA MAb, which had less activity than the IgG1 or IgG3 MAbs, while the IgG4 MAb with identical respective V region genes had no activity.…”