Neisseria meningitidis capsular polysaccharide group A (NmA-CPS)

The Neisseria meningitidis capsular polysaccharide group A is a high-molecular-weight, surface-expressed carbohydrate polymer that forms the protective capsule of *N. meningitidis* serogroup A. It consists of (→6)-α-D-ManNAc-(1→OPO₃⁻→) repeating units, stabilized by phosphodiester linkages and variable O-acetylation at positions C3 and C4, both essential for vaccine-induced immunity. This capsule is the primary virulence factor for serogroup A strains, shielding bacteria from host immune defense and forming the basis for all current group A meningococcal vaccines. Its biosynthesis genes are clustered in the cps locus of the bacterial chromosome. Disruption of capsule expression dramatically reduces pathogenicity, making the NmA-CPS a validated therapeutic and vaccine target. The structure and O-acetylation pattern of the capsule critically influence immunogenicity, vaccine effectiveness, and epidemiological patterns of disease.

Other names

Group A meningococcal capsular polysaccharideSerogroup A polysaccharide capsuleNmA capsuleN. meningitidis serogroup A capsule

Vaccine-induced antibodies bind to the capsular polysaccharide, leading to bacterial opsonization, complement activation, and clearance. Inhibition of capsule synthesis is a proposed (not yet clinically realized) antimicrobial strategy.