Activity and Cross-Reactivity of Antibodies Induced in Mice by Immunization with a Group B Meningococcal Conjugate

Abstract

The capsular polysaccharide of group B Neisseria meningitidis is composed of a linear homopolymer of ␣(2-8) N-acetyl neuraminic acid or polysialic acid (PSA) that is also carried by isoforms of the mammalian neural cell adhesion molecule (NCAM), which is especially expressed on brain cells during development. Here we analyzed the ability of antibodies induced by the candidate vaccine N-propionyl polysaccharide tetanus toxoid conjugate to recognize PSA-NCAM. We hyperimmunized mice to produce a pool of antisera and a series of immunoglobulin G monoclonal antibodies and evaluated their self-reactivity profile by using a battery of tests (immunoprecipitation, immunoblotting, and immunofluorescence detection on live cells and human tissue sections) chosen for their sensitivity and specificity to detect PSA-NCAM in various environments. We also searched for the effects of the vaccine-induced antibodies in two functional assays involving cell lysis or cell migration. Although they were highly bactericidal, all the antibodies tested showed very low or no recognition of PSA-NCAM, in contrast to PSA-specific monoclonal antibodies used as controls. Different patterns of crossreactions were revealed by the tests used, likely due to affinity and specificity differences among the populations of induced antibodies. Furthermore, neither cell lysis nor perturbation of migration was observed in the presence of the tested antibodies. Importantly, we showed that whereas enzymatic removal of PSA groups from the surfaces of live cells perturbed their migration, blocking them with PSA-specific antibodies was not functionally detrimental. Taken together, our data indicated that this candidate vaccine induced antibodies that could not demonstrate an immunopathologic effect.

Protective Immunization against Group B Meningococci Using Anti-Idiotypic Mimics of the Capsular Polysaccharide

“…5). These data are in agreement with previously described work (8,9). A high frequency of polysialic acid-specific mAbs was observed in N-Pr MenB CP-immunized mice after fusion of spleen cells (9).…”

“…A high frequency of polysialic acid-specific mAbs was observed in N-Pr MenB CP-immunized mice after fusion of spleen cells (9). Moreover, a pool of sera from N-Pr MenB TT-immunized mice showed weak, but specific, IgG binding to polysialic acid-rich neural cell adhesion molecule in embryonic brain extracts and on the surface of live cells derived from a mouse pituitary tumor (8). No binding to polysialic acid was detected, however, by other tests.…”

“…The N-Pr CP, however, also elicits a small subset of autoreactive IgGs. Although the concentration and/or avidity of the latter are generally low (8), it may be difficult to prove that such autoantibodies are absolutely innocuous. By the use of mAbs raised against either the N-Pr or the N-Ac CP, at least two different classes of capsular epitopes have been defined, both of which can be found on the intact bacterial surface.…”

Selection of Poly-α 2,8-Sialic Acid Mimotopes from a Random Phage Peptide Library and Analysis of Their Bioactivity

“…Phage Library and Screening-Monoclonal anti-PSA Ab of the IgG 2a isotype directed to Neisseria meningitidis B capsular polysaccharide (19) was immobilized on magnetic protein G beads (protein G Magabeads; Europa Bioproducts, Ltd).…”

Specificity of the Immune Response to a Modified Group B Meningococcal Polysaccharide Conjugate Vaccine

“…This chemical modification has been shown to make the conjugate more immunogenic (2,3,5,6,7,12,14), but the epitope(s) on the bacterial surface recognized by the protective anti-NPrGBMP antibodies is not known (19,20).…”