Polyribosyl ribitol phosphate antigen of Haemophilus influenzae type b (PRP antigen)

The polyribosyl ribitol phosphate (PRP) antigen is a linear capsular polysaccharide forming the outermost layer of encapsulated Haemophilus influenzae type b (Hib) bacteria. It is composed of repeating units of ribose and ribitol phosphate, and is the principal virulence factor of Hib, allowing the bacteria to evade host immune responses by resisting phagocytosis. The antigen is poorly immunogenic on its own, particularly in infants, because it is a T-cell independent antigen. To overcome this limitation, the PRP antigen is covalently conjugated to carrier proteins (such as tetanus toxoid or meningococcal outer membrane protein) in Hib vaccines, inducing a robust, T-cell dependent immune response and protective antibody production. Anti-PRP antibodies are the primary mechanism of protection against invasive Hib disease, which includes meningitis, pneumonia, and septicemia in young children[2][4][5][6]. Key points: - PRP antigen is essential for the pathogenicity of Hib and is the target of effective conjugate vaccines that have virtually eliminated invasive Hib disease where widely used. - It does not function as an enzyme, receptor, transporter, or transcription factor, but as a structural polysaccharide and immune target[2][4][5][6]. - Anti-PRP antibody titers serve as correlates of vaccine-induced protection. - The main therapeutic challenge is the inherently low immunogenicity of unconjugated PRP in young children, which was solved by protein conjugation in modern vaccines[2][4][5][6]. - PRP-based vaccines have no known direct molecular drug interactions (antibiotics kill Hib but do not interact with PRP). The PRP is not a classical drug target but rather a vaccine antigen.

Other names

Hib PRP antigenHaemophilus influenzae type b capsular polysaccharideHib capsulePRP polysaccharide

Induction of protective, neutralizing antibodies when used as a vaccine antigen (PRP-protein conjugate)