The Hib (Haemophilus influenzae type b) conjugate vaccine elicits T-cell-dependent immunity in infants under 2 years, unlike the plain polysaccharide vaccine. This is achieved by:
- A Adding alum adjuvant to the polysaccharide
- B Covalently linking the polysaccharide hapten to a carrier protein (e.g., tetanus toxoid or diphtheria CRM197) which allows T-cell help and immunological memory ✓
- C Using live attenuated Hib organisms as the vaccine strain
- D Incorporating TLR-4 agonist in the formulation
Explanation
Plain polysaccharide antigens are T-cell-independent antigens — they directly stimulate B cells via multivalent BCR crosslinking but do not generate immunological memory and are poorly immunogenic in children < 2 years due to immaturity of the marginal zone B-cell compartment. Conjugate vaccines covalently link the polysaccharide to an immunogenic carrier protein (tetanus toxoid, diphtheria toxoid, or CRM197 mutant diphtheria). This converts the response to T-cell-dependent: carrier peptides are presented on MHC class II to CD4+ helper T cells, providing co-stimulation for B cells, class switching, affinity maturation, and memory cell formation — effective even in infants.
Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.