specific immune response

• 1. Phagocytes detect chemical signals from pathogen (sugars, DNA, proteins) using TLRs
  2. Phagocytes bind to antigens on the pathogen
  3. They engulf the pathogen and form a phagosome
  4. Lysosomes migrate to the phagosome
  5. A phagolysosome forms and lytic enzymes break down and digest the pathogen.
• All cells display proteins on their cell surface known as antigens. These can be recognised by the body as “self” or “non-self”.

  If the body recognises these antigens to be non-self, it triggers an immune response.
• One aspect of the specific immune response is to produce antibodies.  These are Y shaped glycoproteins made of polypeptide chains held together by disulphide bridges. They are referred to as Immunoglobulins.

  
• Antigens bind to antibodies in a lock and key mechanism. This forms an antigen-antibody complex
• Antibodies act as Opsonins, Agglutinins and Anti-toxins
• There are B and T lymphocytes involved in the immune response.
• T Helper cells bind to the antigens on APCs using receptors on their surface membrane (CD4) This stimulates production of interleukins (type of cytokine)

  • stimulate B cells
  • stimulate T cell production
  • stimulates macrophages
• T killer cells produce perforins and their function is for “killing”

  Perforin makes holes in the cell membrane of the pathogen
• T Memory Cells are important for immunological memory. They remember antigens specific to pathogens. This means that they can mount a quick response if a pathogen is encountered for a second time.
• Once a pathogen has been eliminated T regulatory cells suppress the immune response.

  This is vital to prevent the body from attacking “self” cells.
• There are two main forms of immunity- Cell Mediated and Humoral
• Receptors on T helper cells fit the antigens presented by the Antigen presenting cell. These T helper cells also respond to any altered cells (cancer cells, viruses etc)
• B Lymphocytes- mature in the bone marrow

  • plasma cells
  • B memory cells
  • B effector cells
• T Lymphocytes- mature in the Thymus gland

  • T killer cells
  • T helper cells
  • T regulatory cells
  • T memory cells
• Plasma cells produce antibodies (at a rate of 2000 per second!)

  These are specific to the antigen presented by the pathogen.

  Plasma B cells only live for a few days- their antibodies survive for longer than they do.
• B Memory cells have an Immunological memory. They live a long time and remember specific antigens.

  This enables a rapid response if that specific antigen is detected again. If this occurs it triggers formation of appropriate antibodies.
• B effector cells become APCs

  They divide to form plasma B cells to help mount a defence
• The humoral immune response is a response to antigens on the outside of cells. This could be on APCs or on the invading pathogen itself.

  The main difference between the humoral response and cell mediated response is that the humoral produces antibodies.

  The humoral response involves B and T lymphocytes
• B lymphocytes have antibodies on their surface called Immunoglobins (usually M (IgM)).

  These antibodies bind to the complementary antigens on pathogens and like macrophages an APC can be formed. This triggers the humoral pathway
• primary immunity - Where antibodies produced by plasma cells inhibit the pathogen
• clonal selection - Where B effector cells with antibodies complementary to the pathogen's antigens are selected for cloning
• clonal expansion - Where B effector cells rapidly divide into B plasma and B memory cells.
• secondary immunity - Where antibodies produced by memory cells inhibit the pathogen upon second infection.
• T lymphocytes are involved in cell mediated immunity

  Cell Mediated Immunity is the response to cells that have been altered.