Group A Carbohydrate (Streptococcus pyogenes) (GAC)

The Group A Carbohydrate (GAC) is a fundamental cell wall polysaccharide of Streptococcus pyogenes (Group A Streptococcus), accounting for approximately 30-50% of the bacterial cell wall by weight. It is composed of a poly-L-rhamnose backbone with N-acetyl-D-glucosamine (GlcNAc) side chains, which are essential for the bacterium's structural stability, viability, and virulence. GAC facilitates bacterial survival by providing resistance against host innate immune mechanisms, including neutrophil-mediated killing and metal ion toxicity. As the defining antigen for Lancefield Group A classification, it serves as the primary target for rapid antigen detection tests (RADTs) used globally to diagnose streptococcal pharyngitis. In therapeutic development, GAC is a high-priority target for universal conjugate vaccines aimed at inducing protective opsonophagocytic antibodies. However, a significant challenge in targeting GAC is the potential for autoimmune cross-reactivity between its GlcNAc moiety and human tissues, which has led researchers to develop modified, GlcNAc-deficient GAC variants to improve vaccine safety.

Other names

Group A CarbohydrateGACLancefield Group A antigenGroup A streptococcal carbohydrateStrep A carbohydrateGAS cell wall polysaccharide

Induction of opsonophagocytic antibodies to facilitate bacterial clearance; diagnostic antibody binding for pathogen identification.