Polyribosylribitol Phosphate Capsule (PRP)

Polyribosylribitol phosphate (PRP) is the capsular polysaccharide of Haemophilus influenzae type b (Hib). It is a high-molecular-weight polymer composed of repeating ribose-ribitol phosphate units. PRP is a major virulence factor, enabling Hib to evade the host immune system. It is the active component of Hib conjugate vaccines, where it is conjugated to a carrier protein to elicit a protective antibody response. PRP's structure allows it to mask bacterial surface antigens, preventing opsonization and complement-mediated killing. Analytical methods for PRP include ion chromatography and size-exclusion chromatography.

Other names

Haemophilus influenzae type b capsuleHib capsuleCapsular polysaccharide of Hib[→3)-β-D-Ribf-(1→1)-D-Ribtol-(5→OPO₃⁻)]n

PRP is not directly targeted by a drug. Rather, it is used as an antigen in vaccines. Conjugation to a carrier protein enhances immunogenicity, leading to antibody production against PRP and subsequent protection against Hib infection.