Haemophilus influenzae type b polyribosylribitol phosphate (PRP) (Hib PRP)

Haemophilus influenzae type b polyribosylribitol phosphate (PRP) is the primary capsular polysaccharide and a major virulence factor of the Hib bacterium. It functions by protecting the bacteria from phagocytosis and complement-mediated lysis, allowing for systemic invasion and the development of severe diseases such as meningitis, pneumonia, and epiglottitis. The input name, 'Haemophilus influenzae type b PRP–tetanus toxoid conjugate', refers to a vaccine formulation (PRP-T) rather than a biological target; in this context, the PRP polysaccharide is the actual target of the vaccine-induced immune response. Because pure polysaccharides are poorly immunogenic in infants, PRP is chemically conjugated to a carrier protein like tetanus toxoid to create a T-cell dependent antigen. This conjugation enables the induction of high-affinity IgG antibodies and immune memory in young children. These antibodies facilitate the opsonization and killing of the bacteria, providing effective protection against invasive Hib disease.

Other names

Polyribosylribitol phosphateHib capsular polysaccharideHaemophilus influenzae type b antigenPRP

The vaccine induces the production of capsular-specific IgG antibodies (opsonophagocytic antibodies) that bind to the PRP polysaccharide on the surface of the Hib bacterium. This binding facilitates bacterial clearance through opsonization, phagocytosis, and complement-mediated lysis, thereby preventing invasive disease.