Paper I
2025 March (Supplementary (SAY)) (2019 Scheme) · 100 marks · 180 min

Question

Classify immunity. Describe acquired immunity with examples (2+4)

Q66 marksShort Essays

Answer

Classification of immunity

  1. Innate (natural/non-specific) immunity — present from birth, non-specific, no memory generated; includes physical barriers (skin, mucosa), phagocytic cells, complement, and natural killer cells.
  2. Acquired (adaptive/specific) immunity — develops after exposure to a specific antigen, highly specific, generates immunological memory; further subdivided into:
    • Active immunity — the individual’s own immune system produces the response.
      • Natural active — following actual infection.
      • Artificial active — following vaccination.
    • Passive immunity — pre-formed antibody is transferred to the individual (no active response generated).
      • Natural passive — maternal antibody transfer (IgG across placenta; IgA via colostrum/breast milk).
      • Artificial passive — administration of immunoglobulin/antiserum (e.g., tetanus immunoglobulin, anti-snake venom serum).

Acquired immunity, described with examples:

Active immunity develops slowly (days to weeks after exposure) but is long-lasting, since it involves the generation of memory B and T lymphocytes capable of a rapid, strong secondary response on re-exposure to the same antigen.

  • Natural active example: a person who has recovered from chickenpox develops long-lasting (often lifelong) immunity against subsequent varicella infection.
  • Artificial active example: administration of the measles vaccine, stimulating the immune system to generate a protective antibody/memory response without the individual experiencing the actual disease.

Passive immunity provides immediate protection since pre-formed antibody is directly administered/transferred, but the protection is short-lived (weeks), and no memory is generated since the individual’s own immune system was never stimulated to respond.

  • Natural passive example: transfer of maternal IgG antibody across the placenta to the fetus, providing the newborn temporary protection against infections the mother is immune to during the first few months of life.
  • Artificial passive example: administration of tetanus immunoglobulin (TIG) to a patient with a contaminated wound and uncertain/incomplete tetanus vaccination history, providing immediate protection while active immunization is initiated simultaneously.

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