De-N-acetylated sialic acid is immunogenic and elicits antibodies that are protective against Neisseria meningitidis.

Recently, we showed that monoclonal antibodies (mAbs) that are reactive with derivatives of polysialic acid containing de-N-acetylated neuraminic acid (Neu) residues are protective against N. meningitidis group B strains (Moe et al. 2005, Infect Immun73: 2123; Flitter et al., in preparation). In addition, we found that fully de-N-acetylated PSA (i.e. poly alpha 2,8 Neu) conjugated to tetanus toxoid (DeNAc) elicits IgM and IgG antibodies of all subclasses in mice that bind to group B strains, activate human complement deposition, are protective in an infant rat model of meningococcal bacteremia and are bactericidal against group C strains (Moe et al, in press). We show here that anti-DeNAc mAbs, DA1 and DA2 (both IgM), are reactive with polysaccharides containing Neu, bind to group B, C, W135 and Y but not X strains grown in chemically defined media (CDM). However, when the group X strain is grown in CDM supplemented with human plasma, DA2 binds. Also both mAbs mediate bactericidal activity against B, C, W135, and X strains with human complement. The results suggests that N. meningitidis express and/or acquire zwitterionic de-N-acetyl sialic acid antigens that can be the target of protective antibodies.