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Immunity ii

Acquired immunity

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Immunity ii

  1. 1. Acquired (adaptive) Immunity Resistance to infection, developed / adapted / acquired by an individual during life, by virtue of natural infection or immunisation. It depends on prior contact with a pathogen or their antigens; Acquired immunity is of two types: Active immunity – host’s immune apparatus is active; Passive immunity – host’s immune apparatus is passive. 2
  2. 2. Adaptive Immunity is capable of recognising & selectively eliminating specific foreign microorganisms & molecules . Adaptive Immunity displays FOUR characteristic attributes – 1. Antigenic specificity 2. Diversity 3. Immunologic memory 4. Self – nonself recognition 3
  3. 3. ANTIGENIC SPECIFICITY – Permits it to distinguish subtle differences among antigens. DIVERCITY – Capable of generating tremendous diversity in its recognition molecules allowing it to recognise billions of unique structures on foreign antigens. MEMORY – Once it has recognised & responded to an antigen , it exhibits immunologic memory, i.e. a second encounter with the same antigen induces a heightened response. SELF – NONSELF RECOGNITION – Capable of responding only to foreign antigens. 4
  4. 4. 5 resistance developed by an individual as a result of an antigenic stimulus. - host’s immune apparatus is active – synthesis of antibodies &/or immunocompetent cells. Sets in after a latent period; Once developed – lasts longer; - second attack with the same or similar pathogen – quicker, prompt & abundant response; Associated with ‘immunological memory’ More effective & better protection than passive immunisation.
  5. 5. 6 resistance transmitted to an individual passively, in a ‘ready-made’ form. Host’s immune apparatus is passive No antigenic stimulus is required; preformed abs. Are administered; No latent period; protection effective immediately; Lasts for few days or weeks; No secondary response; no ‘immunological memory’ Advantage – acts immediately, hence employed when ‘instant’ protection is desired. Less effective & inferior immunity than active immunisation.
  6. 6. COMPARISON OF ACTIVE & PASSIVE IMMUNITY 7 Active Immunity Passive Immunity Produced actively by host’s immune system Received passively; no active host participation Induced by infection or immunisation ‘Ready-made’ antibodies transferred Durable effective protection Transient, less effective Latent period (Lag phase) required No Latent period; Immediate Immunity Immunological Memory present No immunological Memory Booster effect after subsequent dose Subsequent dose less effective ‘Negative Phase’ may occur No Negative Phase Not applicable in Immunodeficient Applicable in Immunodeficient
  7. 7. 8 ACQUIRED (ADAPTIVE) IMMUNITY Active Passive Natural NaturalArtificial Artificial Infection Vaccination Mother to fetus “Ready-Made” Abs.
  8. 8. 9 Natural active immunity: Results from either a clinical or in apparent infection by a pathogen. A person recovered from an attack of measles develops natural active immunity; Duration of immunity varies according to the pathogen; Life-long with many viral infections ex. Chicken pox & measles; Short-lived with some ex. Influenza & common cold; In typhoid fever – durable immunity; In syphilis – ‘premunition’ immunity.
  9. 9. 10 Artificial active immunity: Resistance induced by vaccines (live or killed or products of mos.) Ex. Bacterial vaccines: Live BCG for tuberculosis, Killed cholera vaccine, Subunit typhoid vi antigen, Bacterial products – tetanus toxoid Viral vaccines: Sabin’s live attenuated OPV, Salk’s killed injectable PV, Subunit hepatitis B vaccine.
  10. 10. 11 Artificial active immunity: contd….. Live vaccines: usually given in single dose; Its immunity parallels natural infection & lasts for years; Administered orally (OPV) or parenterally (BCG). Killed vaccines: less immunogenic than live vaccine; Lasts for a short period; Usually given in multiple doses; First ‘ – sensitises the immune apparatus; Later ‘ required to increase the ab. Level in the circulation; Administered orally (TAB) or parenterally (cholera vaccine).
  11. 11. 12 Artificial active immunity: contd….. Killed vaccines: immune response to primary & secondary doses.
  12. 12. 13 Natural passive immunity: Resistance passively transferred from mother to the fetus. Maternal abs. – Transmitted thro’ the placenta passively; IgG & IgA abs. Transmitted thro’ colostrum, - resist intestinal digestion, gives protection to neonates. Maternal abs. Protects the baby till 3 months of age, from infectious diseases; Passive immunity in infants can be improved by active immunisation of the mother during pregnancy.
  13. 13. 14 Artificial passive immunity: Resistance passively transferred to a recipient by the administration of antibodies. Ex. Hyper immune sera of immunised animals (ATS, ADS or AGS from horse serum) or human being; Convalescent sera – high titers of specific abs; Pooled gamma globulins – abs. For all common pathogens in a region; Used for prophylaxis & therapy of patients with immunodeficiencies.
  14. 14. 15 Artificial passive immunity: contd….. “Passive immunisation is indicated for immediate & temporary protection in a non-immune host, faced with the threat of infection, when there is insufficient time for active immunisation to take effect.” Combined (passive + active) immunisation: usually preferred at ‘emergencies’. Ex. A person with cl. Tetani infection is injected with ATS (passive) & TT (active) for combined immunisation against tetanus
  15. 15. 16 Artificial passive immunity: contd….. Passive immunisation can also be used to suppress active immunity, when the later may be injurious; Ex. Rh immunoglobulins injected in Rh –ve pregnant women to protect Rh +ve fetus.
  16. 16. 17 Artificial passive immunity: contd….. Adoptive immunity: Resistance transferred by injecting immunologically competent lymphocytes; Not practicable; An extract of such cells, known as ‘transfer factor’ are used; Especially attempted for the treatment of lepromatous leprosy.
  17. 17. 18 Local immunity: (Besredka – 1919-22) Immunity operative at a localised site or at the site of entry of the pathogen; May be due to infection or immunisation; Herd immunity: Herd = large population of individuals in a community; Overall level of immunity in a community; relevant to control epidemic diseases; Low herd immunity – epidemics are likely to occur & vice versa; Eradication of communicable diseases depends upon the development of high levels of herd immunity.
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