Polyribosylribitol phosphate (PRP) (PRP)

Polyribosylribitol phosphate (PRP) is the primary capsular polysaccharide and major virulence factor of Haemophilus influenzae type b (Hib), a Gram-negative bacterium. The capsule serves as a protective barrier that allows the pathogen to evade the host immune system by inhibiting phagocytosis and complement-mediated lysis. In its purified form, PRP is a T-cell independent antigen, which makes it poorly immunogenic in infants and young children who have immature immune systems. To overcome this, PRP is covalently linked to carrier proteins in conjugate vaccines to recruit T-cell help, transforming it into a T-cell dependent antigen. This conjugation induces high-affinity IgG antibodies and immunological memory, providing long-term protection against invasive Hib disease. Widespread use of these conjugate preparations has significantly reduced the global burden of life-threatening conditions such as bacterial meningitis, epiglottitis, and pneumonia.

Other names

Hib capsular polysaccharidePolyribosyl-ribitol-phosphatePRP antigenHaemophilus influenzae type b capsular polysaccharide

The vaccine introduces the PRP polysaccharide conjugated to a carrier protein (such as tetanus toxoid or CRM197). This molecular structure allows B-cells to present carrier-derived peptides to T-helper cells, inducing a T-cell dependent immune response. This leads to the production of high titers of protective IgG antibodies and the generation of memory B-cells, which recognize the PRP on the surface of invading Hib bacteria and facilitate their clearance.