Immunology and HIV

• A pathogen is an organism, usually a micro-organism, which causes a disease
• Bacteria are single cell organisms called prokaryotic cells (EG: Cholera, Salmonella)
• Viruses consists of a protein coat and a nucleic acid such as DNA/RNA.N(EG: HIV, common cold, flu)
• Fungi are Eukaryotic organisms which could be single called or filamentous (EG: athlete’s foot, thrush)
• The human body has several defence mechanisms against pathogens such as preventing their entry, inflammation and recognising ‘foreign’ cells.
• An antigen is a molecule (usually a protein) that stimulates an immune response resulting in the production of specific antibodies.
• All cells present antigens either self antigens which our own cells or Non-self antigens which are foreign.
• An Antibody is a protein/glycoprotein made in response to a foreign antigen. It has binding sites which bind specifically to antigen, which are produced by B plasma cells.
• The overall shape of the antibody is ‘Y-shaped’.
• The main structure of an antibody is the heavy chain and is the same in all antibodie.
• The light chain in an antibody is the binding site for antigens and therefore is different from antibody to antibody.
• Due to having specific binding sites, antibodies only bind to specific antigens forming antigen-antibody complexe.
• The phases of phagocytosis are:

  1)Pathogens are engulfed by the phagocyte

  2)The engulfed pathogen enters the cytoplasm of the phagocyte in a vesicle

  3)Lysosomes fuse with vesicles releasing digestive enzymes

  4)Lysosomes enzymes(hydrolytic enzymes) break down the pathogen

  5)waste materials are ejected from the cell
• Phagocytosis is non specific and targets any ‘foreign’ entities within the body.
• Specific immunity is a specific response to a specific antigen on the surface of a cell or pathogen that has be recognised as non self (foreign)
• Specific immunity involves Lymphocytes, which are smaller that phagocytes and have a large nucleus that fills most of the cell.
• Lymphocytes are produced in the bone marrow before birth
• Specific Immunity: (T cells)

  1)T-lymphocytes are activated when they encounter and bind to their specific antigen presented on a hosts cell (EG: phagocyte, infected cell)

  2)The T-lymphocytes that have bound to a antigen presenting cell divide by mitosis.

  3) The T-lymphocytes differentiate into two main types of T cell (T Helper cells and Cytotoxic (killer) T cells)
• Helper T cells assist other white blood cells in the immune response when they release cytokines (hormone-like signals)
• Cytokines stimulate:

  1)the maturation of B-lymphocytes into antibody-secreting plasma cells

  2)production of memory B cells

  3)activation of cytotoxic (killer) T cells which destroy virus infected and tumour cells

  4)an increased rate of phagocytosis
• Cytotoxic (Killer) T cells kill infected cells.
• The humoral response involves the activation of B cells to produce antibodies.
• B Lymphocytes - Humoral Response:

  1)The surface antigens of an invading pathogens are taken up by a specific B cell

  2)The specific B lymphocyte presents the antigens on its surface.

  3) A T Helper cell with a complementary receptor binds to the presented antigen and activates the B cell to clone (clonal selection)

  4)The specific B cell divides by mitosis producing B plasma cells which secrete the specific antibody that fits on the pathogens surface.
• B cells can divide by mitosis to produce plasma and memory B cells. B memory class remain circulating in the blood for a long time and allow for a quicker response if re infected (secondary response)
• Aggulation is when antibodies bind to the antigens on pathogens and clump them together allowing phagocytes to recognise and destroy the pathogen more efficent (enhanced phagocytosis)
• Antibodies destroy bacteria by binding to the bacteria’s surface and damaging its cell membrane casing the cell to undergo lysi.
• The secondary immune response is similar to the primary immune response but this time the memory cells recognise the antigen and divide quickly into plasma cells and produce more memory cells.
• The activation of memory cells to produce antibodies is known as the secondary immune response and is both quicker and more extensive.
• Antigenic variability is a change in the antigen shape or structure (tertiary structure) that is caused by genetic mutations which makes it difficult to develop vaccines against specific pathogens.
• Passive immunity has 4 characteristics:

  1)It does not involve memory cells

  2)It is short term as the antibody is broken down

  3)Fast acting

  4)The antibodies are received from elsewhere (not produced by the individual)
• Artificial passive immunity occurs when people are given an injection/ transfusion of the antibodies.
• Natural passive immunity occurs when Foetuses receive antibodies across the placenta or babies revive the initial breast milk from their mothers.
• There are r characteristics of Active immunity:

  1)The immunity is provided by memory cells that are produced after a primary immune response to a pathogens antigen

  2)Involves the production of antibodies form plasma cells

  3)It is naturally acquired

  4)It provides long term immunity
• In active immunity during the primary response to a pathogen or vaccination the antibody concentration in the blood takes one or two weeks to increase.
• Vaccines are not effective against pathogens which show antigenic variability
• Antigenic concealment is when a pathogen hides from the immune system by living inside cells or when the pathogen coast their bodies in host protein.
• Vaccines will initiate a primary immune response
• A vaccine is a suspension of antigens that are intentionally put into the body to induce artificial active immunity.
• Herd immunity is when enough individuals in the population are vaccinated then there is little chance of the disease spreading and therefore non-vaccinated individuals are protected.
• Monoclonal antibodies all have the same tertiary structure and they bind specifically to only ONE antigen.