Specific Immune system

• Humoral Immunity = body responds to antigens found outside of the cell (e.g. bacteria or fungi)
• Humoral Immunity:

  • B cell with complementary antibody binds to pathogen, engulfs it and processes its antigens becoming an APC
  • activated T helper cell binds to B cell APC (clonal selection)
  • T helper cell produces interleukins to activate B cell
  • B cell divides into plasma cells and B memory cells (clonal expansion)
  • plasma cells produce antibodies that fit the antigens on the pathogens surface
• Cell-mediated Immunity = responds to cells that have been changed (e.g. by a virus or mutation)
• Cell-mediated Immunity:

  • macrophages engulf pathogens, process the antigens and become APCs
  • receptors on some T helper cells will fit the antigens
  • these T helper cells become activated and release interleukins to stimulate more T cells to divide
  • these cloned T cells may develop into T memory cells, produce interleukins to stimulate phagocytosis or to stimulate B cells to divide or develop into T killer cells and destroy infected cells
• How antibodies defend the body:

  • act as opsonins (tag pathogens so the complex is engulfed by phagocytosis)
  • act as agglutinins (clump together pathogens preventing them from spreading + allowing multiple to be engulfed at once)
  • act as anti-toxins (bind to toxins produced by pathogens and make them harmless)
• T helper cells = receptors bind to antigens, produce interleukins, interleukins stimulate B cells (increases antibody production, stimulates production of other types of T cells and attracts macrophages to engulf pathogens)
• T killer cell = produce perforin which kills pathogens by creating holes in their cell membrane
• T memory cells = live for a long time, rapidly divide into T killer cells if a pathogen is encountered again
• T regulatory cells = suppress the immune system once a pathogen has been destroyed and makes sure the body recognises self antigens
• Plasma cells = produce antibodies to a particular antigen
• B effector cells = divide to form plasma cell clones
• B memory cells = enable a rapid response if a pathogen is encountered again
• Antibodies = Y-shaped glycoproteins called immunoglobulins
• Antibodies:

  • made up of polypeptide chains - two heavy chains and two light chains
  • Chains are held together by disulfide bridges
  • variable region - antigen binding site
  • constant region - same on every antibody
• Cell-mediated immunity:

  • Macrophages engulf and digest pathogens in phagocytosis and process the antigens to form antigen presenting cells (APCs).
  • The receptors on some of the T helper cells fit the antigens. These T helper cells become activated and produce interleukins which stimulate T cells to divide rapidly by mitosis.
  • The cloned T helper cells may; develop into T memory cells, produce interleukins that stimulate phagocytosis, produce interleukins that stimulate B cells to divide or develop into T killer cells and destroy infected cells.
• Humoral Immunity:

  1. A B cell with the complementary antibody will bind to the pathogen, engulf it and process the antigens to become an APC
  2. Activated T helper cells bind to the B cell APC (clonal selection)
  3. Interleukins produced by the activated T helper cells activate the B cells
  4. The activated B cells divide to give clones of plasma cells and B memory cells (clonal expansion)
• Humoral Immunity:

  Cloned plasma cells produce antibodies that fit the antigens on the surface of the pathogen, bind to the antigens and disable them or act as opsonins or agglutinins. (primary immune response)Some cloned B cells develop into B memory cells. If the body is infected by the same pathogen again, the B memory cells divide into plasma cell clones. These produce the right antibody and wipe out the pathogen quickly. (secondary immune response)
• B lymphocytes mature in the bone marrow.
• T lymphocytes mature in the thymus gland.
• T helper cells = produce interleukins (a type of cytokine- cell-signalling molecule). These interleukins stimulate the activity of B cells and stimulate the production of other T cells.
• T killer cells = these destroy the pathogen carrying the antigen. They produce perforin, which kills the pathogen by making holes in the cell membrane so it is freely permeable.
• T memory cells = live for a long time so if they meet an antigen a second time, they divide rapidly to form a huge number of clones of T killer cells that destroy the pathogen.
• T regulatory cells = these cells suppress the immune system, acting to control and regulate it. They stop the immune response once a pathogen has been eliminated, and make sure the body recognises self antigens and does not set up an autoimmune response.
• Plasma cells = produce antibodies to a particular antigen and release them into the circulation.
• B effector cells = these divide to form the plasma cell clones
• B memory cells = programmed to remember a specific antigen and enable the body top make a very rapid response when a pathogen carrying that antigen is encountered again.
• Antibodies are Y-shaped glycoproteins called immunoglobulins which bind to a specific antigen on the pathogen or toxin that triggered the immune response. There is a specific antibody for each antigen.
• Antibodies are made up of two identical long polypeptide chains called the heavy chains and two much shorter identical chains called the light chains. The chains are held together by disulfide bridges and there are also disulfide bridges within the polypeptide chains holding them in shape.
• How antibodies defend the body:

  1. The antibody of the antigen-antibody complex acts as an opsonin so the complex is easily engulfed and digested by phagocytes
  2. Most pathogens can no longer effectively invade the host cells once they are part of an antigen-antibody complex
  3. Antibodies act as agglutinins causing pathogens carrying antigen-antibody complexes to clump together. This prevents them spreading through the body and makes it easier for phagocytes to engulf a number of them at the same time
  4. Antibodies act as anti-toxins binding to the toxins produced by pathogens making them harmless
• Parasite = lives on host, feeds from host, and causes harm to host
• Autoimmune disease = a disease where the immune system attacks own body cells as it recognises them as foreign (body cells have become antigenic)