- Skin is composed of dead cells containing the indigestible protein keratin
- Sebum produced by the skin lowers the pH to inhibit growth of pathogens
- Lysozymes in salvia, sweat and tears are anti-bacterial enzymes
- Many ingested bacteria in the stomach are destroyed by acid (HCl)
- A sticky substance, mucus, traps pathogens in the respiratory tract
- Cilia moves away mucus towards the throat to protect gas exchange surfaces
- The immune system targets foreign materials and pathogens
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Inflammatory response |
- Histamine is released into the wound by white cells
- This increases vasodilation and increases vascular permeability
- Vasodilation increases the local blood flow → area becomes red, warm
- Increased permeability allows escape of tissue fluid into the tissues
- Tissue fluid contains plasma proteins (antibodies) and may cause swelling
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Phagocytosis |
- White cells (phagocytes) contain digestive enzymes within lysosomes
- Neutrophils primarily engulf bacteria
- Macrophages engulf larger particles; including old and infected red blood cells
- Found in blood, lymph systems and tissues
- Squeeze through gaps in the walls of venules to enter tissues
- This allows them to move faster to tissues infected with pathogens
- Phagocytes are attracted by chemotaxis
- Opsonisation by antibodies (bacteria becomes coated with antibody)
- As a result, binding between bacteria and phagocytes is improved
- Phagocytes form pseudopodia around the particle
- This positions the particle into a phagocytic vacuole (also called phagosome)
- Lysosome fuses with the phagosome
- Intracellular killing by digestive enzymes from the lysosome
- Pus if formed at the site of infection if no extensive vasculature is present
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Blood clotting |
If blood vessels are damaged a series (cascade) of enzyme-control reactions occurs to form a clot
a) Prevents further blood loss
b) Prevents invasion by pathogens
- Clotting depends on clotting factors which are plasma enzymes
- They are present as an inactive form in blood plasma
- They are named with roman numerals e.g. Factor V
- Haemophilia is an inherited disease. Patients make non functional Factor VIII
- Serotonin causes smooth muscle of the arterioles to contract / narrows blood vessels, cutting off the
blood flow to damaged area
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Principle of immunology |
| Antigen |
- Molecule that stimulates an immune response
- Usually proteins (polysaccharides, nucleic acid, lipids can also act as antigens) and other inorganic molecules important for self-recognition
- Self-antigen
- Only found on the host's own cells and does not trigger an immune response
- As these are proteins, their structure depends on the amino acid sequence
- The gene for this sequence is highly polymorphic, having several alleles at each loci
- There is great genetic variability between individuals
- \ Antigen is different in other people → would cause an immune response
- There is only 1:4 change that siblings will possess an identical antigen
- Non-self-antigen
- Found on cells entering the body (e.g. bacteria, viruses, another person's cell)
- Will cause an immune response
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Antibody (immunoglobin protein) |
- Secreted by B-lymphocytes and produced in response to a specific (foreign) non-self antigen
- B-lymphocyte's receptor site matches the non-self-antigen
- Each antibody is produced by one type of B-lymphocyte for only one type of antigen
- An antibody is Y-shaped
- The two ends of the Y are called the Fab fragments
- The other end is called the Fc fragment
- Fab fragment is responsible for the antigen-binding properties
- Fc fragment is the effector component and triggers the immune response
- B cells divide and form memory cells and antibody-secreting plasma cells:
- Agglutination makes pathogens clump together
- Antitoxins neutralise toxins produced by bacteria
- Lysis digests bacterial membrane, killing the bacterium
- Opsonisation coats pathogen in protein that identifies them as foreign cells
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Types of Immune Response |
- Lymphocytes undergo maturating before birth, producing different types of lymphocytes
- Humoral response - B lymphocytes
- Produce and release antibodies into blood plasma
- Produce antibodies from B plasma cells
- Recognize foreign antigen directly
- Cellular response - T lymphocytes
- Bind to antigen carrying cells and destroy them and/or activate the humoral response
- Recognize foreign antigens displayed on the surface of normal body cells
- Primary response produces memory cells which remain in the circulation
- Secondary response new invasion by same antigen at a lower state. Immediate recognition and distraction by memory cells - faster and larger response usually prevents harm
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B-Lymphocytes: The Humoral Response |
- Response for pathogens not entering our cells (e.g. bacterium)
- Each B-lymphocyte recognizes only one specific antigen / need T-helper cell to be activated
- Maturation / B-cells develop to give many different variants / specific immune system responds to
any type of pathogen entering the body
- Primary response:
- Pathogen is ingested by macrophages / macrophage displays the pathogens surface non-self antigen on its surface (antigen presentation)
- It then joins with specific T-helper cells and B lymphocytes that have membrane receptors and are complementary in shape to the non-self antigen
- T-helper cells will release cytokines to activate selected B-cell/lymphocyte
- Secretes antibodies of the same type into the blood
- Divided by mitosis to produce a clone
- Cells grow to form plasma cells producing masses of free antibodies
- Some of the cells remain in the blood as memory cells.
- Secondary response = new invasion by same antigen at lower state. Immediate recognition and distraction - faster, larger response usually prevents harm. Antibodies are produced more rapidly and in larger amounts
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T-Lymphocytes: Cell-Mediated Response |
- Virus enter cell and more difficult to remove
- No antibodies involved / work directly on the infected cell by destroying it
- Special proteins called Major Histocompability Complex (MHC) are present on all human cells
- Non-self antigen interacts with MHC as human cell becomes infected by a pathogen
- Specific T-lymphocyte recognises specific non-self antigen only with a chemical marker next to it (MHC)
- Activated T-lymphocytes multiply by mitosis and enter circulation
- Cells differentiate into different types of cell
- Cytotoxic T-Cells destroy pathogens and infected cells by enzyme action, and secrete chemicals which attract and stimulate phagocytes
- Helper T-Cells stimulate the activity of the cytotoxic T-Cells and B-lymphocytes by releasing chemicals (cytokines and interleukins). Destroyed by HIV
- Suppressor T-Cells switch off the T and B cell responses when infection clears
- Memory T-Cells Some activated T-Cells remain in the circulation and can respond quickly when same pathogen enters body again
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Table 3-12-3: Different types of immunity
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Active (Antibodies made by the human immune system, long term acting due to memory cells) |
Passive (Given-Antibodies, short term acting) |
| Natural |
- Response to disease
- Rejecting transplant |
- Acquired antibodies
(via placenta, breast milk) |
| Artificial (immunisation) |
- Vaccination
(Injection of the antigen in a weakened form) |
- Injection of antibodies from an artificial source, e.g. anti venom against snake biter |
| Differences |
- Antibody in response to antigen
- Production of memory cells
- Long lasting |
- Antibodies provided
- No memory cells
- Short lasting |
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How vaccines produce responses by the immune system |
| Artificial active immunity |
| Types of vaccine |
- Vaccine containing dead pathogens. Antigen is still recognised and an immune response made
- Salk polio vaccine (Polio vaccine is injected)
- Influenza
- Whooping cough
- Vaccine containing a toxin
- Vaccine containing an attenuated (modified or weakened) organism which is alive but has been modified so that it is not harmful
- Sabin polio vaccine (Taken orally, often sugar pumps)
- Purified antigen - genetically engineered vaccine
- Hepatitis B (A gene coding for a surface protein of the hepatitis B virus has been inserted into yeast cells which produce the protein when grown in fermenters)
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