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Immune Response

recognise phagocytes and lymphocytes under the light microscope; describe the origin, maturation and mode of action of phagocytes

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Immune Response

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  1. recognise phagocytes and lymphocytes under the light microscope; describe the origin, maturation and mode of action of phagocytes explain the meaning of the term immune response; distinguish between B- and T-lymphocytes in their mode of action in fighting infection and describe their origin and functions relate the molecular structure of antibodies to their functions explain the role of memory cells in long-term immunity; distinguish between active and passive, natural and artificial immunity and explain how vaccination can control disease discuss the reasons why vaccination has eradicated smallpox but not measles, TB, malaria or cholera

  2. Many pathogens cannot cause disease due to non-specific barriers (physical, chemical) and cellular defences, that prevent them from entering the body. If they do enter, the immune system (the specific immune response) can prevent them from spreading through the body Body has three lines of defence against pathogens: 1stBarriers preventing entry - non-specific PhysicalSkin – physical barrier (keratinised) impermeable Mucociliary escalator – airways (mucus and cilia) Reflexes - sneezing; coughing; blinking Chemical Sebum – antibacterial fatty acids (acidic) – pH 5.4 Tears – lysozyme – destroys bacterial cell wall HCl acid – gastric juice; lactic acid - vagina 2ndNon-specific responses Inflammatory response –phagocytes and chemicals Phagocytosis – phagocytes (+ intracellular chemicals) Blood clotting (haemostasis) 3rdSpecific response (specific for pathogen or toxin) Immune response – active and passive immunity T and B cells (lymphocytes – WBC’s)

  3. Immune Response Specific (adaptive / acquired) Specific for particular initiating Ag Adaptive – mechanism of eradication dependent on nature of Ag (blood-borne – by antibodies; intracellular – e.g. viruses – by specific effector cells) Eradicate Ag rapidly and effectively Immunological memory to future infection – to prevent re-infection Non-specific (innate / natural) Response is always of similar magnitude Does not discriminate No memory of encountered Ag (foreign agent) If innate is breached – adaptive immune system responds

  4. 1st Line of defence Skin Dry; composed of dead cells containing keratin (protein) – keratin cannot be digested easily – protective barrier to pathogens; outer layer of cells are shed taking bacteria with them. Microbes can only penetrate when surface is broken; shedding of skin Sebum (sebaceous glands) contains long chain fatty acids – lowers pH (acidic- pH 5.4) – inhibits growth of microorganisms and viruses Sweat (sweat glands) – contains lysozyme – digests cell wall of bacteria Tears – lysozyme and washing action Gut Saliva – lysozyme; amylase HCL acid in stomach – destroys ingested bacteria Mechanical flushing – due to movement of contents and fibre Respiratory tract Mucus (goblet cells) – traps particle and microorganisms Cilia – sweeps mucus towards throat Urinary/Reproductive tract Semen (male) – spermine – antibacterial Vagina – mucus membrane - acidic (lactic acid) Urethra – acidic (due to acidic urine); washing action of urine

  5. 2nd Line of Defence Non specific responses Inflammatory response Phagocytosis Blood clotting Phagocytosis flow chart Phagocytes – originate from bone marrow / foetal liver • Pathogen recognised as foreign – pathogen is antigenic; chemotaxis • Pathogen attached to phagocyte by antibody and surface receptors • Engulfed by phagocyte by endocytosis – invagination of plasma cell membrane to form a phagosome (a membrane bound vesicle containing the pathogen) • Lysosomes (containing lysins & hydrolytic enzymes) fuse to phagosome • Release of H2O2, HCl, free radicals into phagosome • Digest pathogen – harmless products removed (egested / excreted) or used by phagocyte • Phagocyte also displays antigenic components on external surface of plasma cell membrane (antigen presentation) to start immune response

  6. 3rd Line of Defence – Immune Response (Specific) Immune Response Body’s reaction to a foreign antigen or pathogen Antigen Substances capable of eliciting the immune response (production of antibodies – which are usually proteins – termed immunoglobulins). Any agent (foreign) to which an Ab can bind Antibody Immunoglobulin (proteins) produced in response to antigen during the immune response Agglutinate (clump) pathogens (antigens) – for easier phagocytosis Coat pathogen – to attract other chemicals (termed complement proteins), that destroy the pathogen Neutralize toxins Five classes – IgA; IgD; IgM; IgE; IgA Fulfil a specific role within days after encountering Ag Hb – long term evolution to fulfill role

  7. Immunity Passive Ab mediated No immune response – Ab’s not made - come from other source No exposure to Ag Immediate protection Short-term protection No memory cells produced Active Exposure to Ag Ag (pathogen) invades body Lag phase before protection develops Long-term protection Memory cells produced Artificial Vaccination Natural Infection • Artificial • Administration of pre-formed Ab’s • Tetanus injection • Rabies injections • Anti-venom Ab’s Natural Transfer of maternal Ab’s to foetus/baby via milk or through placenta

  8. art; pas art; pas art; act nat ; act art; act nat; pas art; act nat ; act art; act nat; pas

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