Topic 11 - Animal physiology

• Antigens are foreign molecules that trigger an immune response
• The most common antigens are proteins and large polysaccharides
• Antigens are found on surface of cancer cells, bacteria and pollen grains
• In blood types A and B antigen H is modified by the addition of an additional molecule
• If additional molecule is galactose, antigen B results
• If additional molecule is N-acetylgalactosamine, antigen A results
• If a recipient’s transfusion involves the wrong blood type, the immune response is agglutination followed by hemolysis and coagulation of blood in the vessels
• 1. Pathogens are ingested by macrophages and antigens from them are displayed in macrophage plasma membranes
• 2. Helper t cell specific to the antigen binds to macrophage with its receptor proteins and is activated
• 3. The activated T cell binds to lymphocytes specific to antigen called B cells
• Plasma cells secrete antibodies
• Plasma cells are mature B lymphocytes that secrete antibodies during an immune response
• Plasma cells have many rER 
• Activated B cells multiply to form a clone of plasma cells and memory cells
• Clonal selection

  Activated B cells divide many times generating a clone of plasma cells that produce the same antibody
• Antibodies persist in body for a few weeks or months, then are lost after infection has been overcome and antigens are no longer present
• Small number of B cells divide to form memory cells which remain long after infection 
• Memory cells are inactive until same pathogen infects the body again
• Immunity to a disease involves having antibodies against the pathogen or memory cells that rapidly produce the antibody
• Antibodies aid in the destruction of pathogens
• Opsonisation

  Makes a pathogen more recognisable to phagocytes so they are more readily engulfed 
• Toxin neutralisation

  Some antibodies can bind to toxins produced by pathogens, preventing them from affecting cells
• Virus/bacteria neutralisation

  Antibodies can prevent viruses from docking to host cells so they cannot enter the cell
• Complement activation

  Antibodies bound to pathogen surface activate a cascade complex, forming a pore in the pathogen membrane allowing water and ions to enter, causing the cell to be lysed
• Agglutination

  Antibodies cause pathogens to stick together, preventing them from entering cells and making them easier for phagocytes to ingest
• Immunity depends upon persistence of memory cells
• Memory cells ensure that second time an antigen is encountered, body produces more antibodies faster
• Vaccines contain antigens that trigger immunity but do not cause the disease
• Vaccines either contain a weakened version of the pathogen or a derivative that contains the antigens 
• Vaccine stimulates primary immune response, if pathogen enters it will be destroyed by antibodies in a secondary immune response
• Pathogens can be species-specific but some can cross species barriers
• A zoonosis is a pathogen that can cross the species barrier
• Major factor contributing to increased zoonotic diseases is close contact between humans and animals
• Leucocytes release histamine in response to allergens
• Mast cells in connective tissue and basophils secrete histamine
• Histamine cause dilation of blood vessels in an infected area, causing them to become leaky
• Dilation of vessels increases the flow of fluid containing immune components to and from the infected area
• Histamines cause allergic symptoms 
• Cells in a variety of tissues have membrane-bound histamine receptors
• Histamine plays a role in bringing on the symptoms of allergy in the nose