Paper I
2013 September (Supplementary) (2010 Scheme) · 40 marks · 120 min

Question

Active immunity.

Q72 marksShort Notes

Answer

Active immunity is the resistance to infection that develops when an individual’s own immune system is stimulated to produce antibodies and/or sensitized lymphocytes in response to an antigen — it is slow in onset (takes days to weeks to develop) but is long-lasting, often for years, because it involves the formation of immunological memory.

Types:

  • Natural active immunity — acquired following actual clinical or subclinical infection (e.g., immunity after recovering from measles or chickenpox).
  • Artificial active immunity — acquired by deliberate immunization with a vaccine (live attenuated, killed/inactivated, toxoid, or subunit vaccine), which stimulates the immune system without necessarily causing disease.

Key characteristics: slow onset (requires time for clonal expansion of B/T cells), but durable protection, often reinforced by booster doses; generates immunological memory (memory B and T cells) providing a faster, stronger secondary response on re-exposure — the basis of vaccination programmes.

This contrasts with passive immunity (ready-made antibody transferred from another source — e.g., maternal antibody across the placenta, or immunoglobulin/antitoxin injections), which acts immediately but is short-lived since no memory is generated and the transferred antibody is gradually catabolised.

Other Years Asked


Revise MBBS
Preview