Neisseria meningitidis capsular group A polysaccharide (NmA-CPS)

The **Neisseria meningitidis capsular group A polysaccharide** is a homopolymer of (α1→6)-linked N-acetylmannosamine-1-phosphate, forming the external capsule of *N. meningitidis* serogroup A. This capsule is the **primary virulence determinant**, protecting the bacterium from complement-mediated killing and phagocytosis. Its unique structure distinguishes serogroup A from other meningococcal serogroups (e.g., B, C, W, and Y) and forms the antigenic basis for both epidemiological typing and vaccine development. The polysaccharide is highly immunogenic and, when isolated or conjugated to a carrier protein, is the active ingredient in group A meningococcal vaccines, which have been critical for controlling epidemics of meningococcal meningitis, especially in the African meningitis belt. Modifications such as O-acetylation of the capsule influence immunogenicity and vaccine efficacy. Genes encoding for biosynthesis and export of the group A capsule are located in the **cps locus** of the bacterial chromosome.

Other names

Group A meningococcal capsular polysaccharideMenA polysaccharideNmA-CPSSerogroup A meningococcal capsule

Vaccine-induced antibody responses against the group A capsular polysaccharide lead to complement-mediated lysis and phagocytic clearance of *Neisseria meningitidis* serogroup A. Conjugation to carrier proteins (in conjugate vaccines) induces a T-cell-dependent immune response, enhancing immunological memory.