A conjugate vaccine against Haemophilus influenzae type b (Hib) links polysaccharide antigen to a carrier protein. The immunological rationale for conjugation is to:
- A Convert a T-independent antigen to a T-dependent antigen, enabling class switching and memory ✓
- B Increase polysaccharide antigen half-life by reducing renal clearance
- C Prevent polysaccharide degradation by complement in the bloodstream
- D Allow presentation by MHC class I for cytotoxic T cell activation
Explanation
Polysaccharide antigens alone are T-independent (TI-2) antigens that activate B cells directly via BCR cross-linking without T helper cell involvement. This results in IgM-predominant responses without class switching to IgG, no germinal centre reactions, no somatic hypermutation, and no immunological memory. Conjugating the polysaccharide to a protein carrier (e.g., diphtheria CRM197, tetanus toxoid) converts it to a T-dependent antigen, recruiting CD4+ T helper cells, enabling isotype class switching (IgM to IgG), affinity maturation, and long-lived memory B cell formation.
Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.