Haemophilus influenzae type b capsular polyribosyl ribitol phosphate polysaccharide (Hib PRP polysaccharide)

The Haemophilus influenzae type b capsular polyribosyl ribitol phosphate polysaccharide (PRP) is a **linear copolymer** of repeating units comprised of β-D-ribofuranose and D-ribitol linked by (3→5) phosphate diester bonds. The capsule enables the bacterium to evade host immune mechanisms and is a major virulence factor responsible for invasive disease. The PRP is poorly immunogenic on its own in infants, but when chemically conjugated to a carrier protein (such as tetanus toxoid or CRM197), it becomes highly immunogenic, inducing protective, long-lived, T-cell dependent antibody responses. This property forms the basis of Hib conjugate vaccines, which have dramatically reduced the incidence of Hib disease globally[2][3][7][8]. The PRP is used in biological assays as a standard for vaccine characterization, and antibody titers against PRP serve as biomarkers for infection risk and vaccine efficacy[4][7]. Safety concerns are minimal relative to disease risk; rare hypersensitivity reactions may occur[8], but overall, Hib PRP conjugate vaccines are considered safe and essential in pediatric immunization.

Other names

PRPHib capsulePolyribosyl ribitol phosphateHaemophilus influenzae type b polysaccharide capsule

Vaccine-induced antibodies bind PRP, promoting complement-mediated killing and phagocytosis. The conjugation to carrier protein induces T-cell dependent immunity, allowing effective antibody response even in young children[7][8].