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 Tlymphocytes 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
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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:
1st
Barriers preventing entry - non-specific
Physical
Chemical
Skin – physical barrier (keratinised) impermeable
Mucociliary escalator – airways (mucus and cilia)
Reflexes - sneezing; coughing; blinking
Sebum – antibacterial fatty acids (acidic) – pH 5.4
Tears – lysozyme – destroys bacterial cell wall
HCl acid – gastric juice; lactic acid - vagina
2nd
Non-specific responses
Inflammatory response –phagocytes and chemicals
Phagocytosis – phagocytes (+ intracellular chemicals)
Blood clotting (haemostasis)
3rd
Specific response (specific for pathogen or toxin)
Immune response – active and passive immunity
T and B cells (lymphocytes – WBC’s)
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Immune Response
Non-specific (innate / natural)
Specific (adaptive / acquired)
Response is always of similar magnitude
Does not discriminate
No memory of encountered Ag (foreign
agent)
Specific for particular initiating Ag
Adaptive – mechanism of eradication
dependent on nature of Ag (bloodborne – by antibodies; intracellular –
e.g. viruses – by specific effector
cells)
Eradicate Ag rapidly and effectively
Immunological memory to future
infection – to prevent re-infection
If innate is breached – adaptive immune system responds
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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
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2nd Line of Defence
Phagocytosis flow chart
Non specific responses Inflammatory response
Phagocytosis
Blood clotting
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
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membrane (antigen presentation) to start immune response
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
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Immunity
Active
Exposure to Ag
Ag (pathogen) invades body
Lag phase before protection develops
Long-term protection
Memory cells produced
Natural
Infection
Artificial
Vaccination
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
Natural
Transfer of maternal
Ab’s to foetus/baby
via milk or through
placenta
Artificial
Administration of
pre-formed Ab’s
•Tetanus injection
•Rabies injections
•Anti-venom Ab’s
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art; pas
art; act
nat ; act
art; pas
art; act
nat ; act
art; act
nat; pas
art; act
nat; pas
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