A pneumococcal polysaccharide vaccine (PPSV23) fails to induce protective immunity in a 10-month-old infant. The primary immunological reason is:
- A Deficiency of complement C3 in infants under 1 year
- B Absent bone marrow plasma cells in infants
- C Immature marginal zone B cells unable to mount T-independent responses ✓
- D Suppression of polysaccharide response by maternal T cells
Correct answer: C. Immature marginal zone B cells unable to mount T-independent responses
Explanation
The marginal zone of the spleen, which houses B cells responsible for T-independent polysaccharide responses, is functionally immature in children under 2 years. This developmental immaturity explains why plain polysaccharide vaccines fail in infants. Conjugate vaccines overcome this by converting the response to T-cell-dependent via the carrier protein.
Reference: Janeway's Immunobiology, 9th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.