Neisseria meningitidis serogroup B capsular polysialic acid (NmB polysialic acid)

Neisseria meningitidis serogroup B capsular polysialic acid is a homopolymeric, (α2→8)-linked polymer of N-acetylneuraminic acid (sialic acid) that forms a capsule enveloping the bacterium. This capsule enables the bacteria to evade innate and adaptive immune responses by resisting complement-mediated lysis and phagocytosis; it interferes with antibody access to other surface antigens and modulates complement deposition. The capsule is a critical virulence determinant in group B meningococci and is, therefore, a major target for vaccine design. However, vaccines based directly on this polysaccharide have proven challenging because the epitope is poorly immunogenic and mimics human neural cell polysialic acid, raising difficulties in generating effective and safe immune responses. For this reason, vaccines against group B meningococcus typically exploit protein antigens rather than targeting the capsule directly, unlike vaccines for serogroups A, C, Y, and W-135.

Other names

Meningococcal group B polysaccharideGroup B capsular polysialic acidNmB polysialic acidSerogroup B polysaccharide(α2→8)-linked polysialic acid capsule

Vaccine-induced antibodies bind to the capsular polysialic acid and promote complement-mediated bactericidal activity. Some experimental monoclonal antibodies may promote opsonization or neutralize the capsule’s immune evasion properties.