cell-mediated response

• T lymphocytes (T cells)

  • lymphocytes are white blood cells involved in the specific immune response
  • all lymphocytes are made in the bone marrow, but T lymphocytes cells mature in the thymus.
  • the cell-mediated response is the response involving T cells and body cells.
• antigen presenting cells (APC)

  • the cell-mediated response is specific because T cells respond to antigens on the surface of cells.
  • APC: any cell that presents a non-self antigen on their surface:
  • a macrophage which has engulfed and destroyed a pathogen will present the antigens on their surface.
  • cells of a transplanted organ will have different shaped antigens on their surface compared to your self-cell antigens.
  • cancer cells will have abnormal shaped self-cell antigens.
• cell-mediated:

  T cells responses are described as cell-mediated because T cells only respond to antigens which are presented on cells (APC), and not antigens detached from cellss and within body fluids e.g. blood.
• the cell-mediated response:

  1. once a pathogen has been engulfed and destroyed by a phagocyte, antigens are postitioned on the cell surface- an antigen presneting cell (APC)
  2. helper t cells have receptors on their surface which attach to the antigens on APC
  3. once atatched this actviates the helper T cells to divide by mitosis to repliacte and make large numbers of clones
  4. cloned helper T cells differentiate into different cells. some remain T cells and activate B lymphocytes, stimulate macrophages to perform more phagocytosis, memory cells for that shaped antigen,become cytotoxic T cells
• cytotoxic T cells:

  • destroy abnormal or infected cells
  • they release a protein, perforin, which embeds in the cell surface membrane and make a pore so that any substance can enter or leave the cell.
  • this causes cell death (cell shrivels or lyse)
  • this is most common in viral infections because viruses infect body cells.
  • body cells are sacrificed to prevent viral replication.
• on the surface membrane of T lymphocytes we find the T cell receptor. the job of the cell receptor is to attach to an antigen
• T helper cell is activated when a T helper cell with the correct T cell receptor now attaches to the surface antigen. it then undergoes mitosis producing identical clones. the activated T helper cells also produce cytokine molecules called interleukins.
• interleukins can trigger phagocytes to increase their rate of phagocytosis and also stimulate B lymphocytes to divide by mitosis.
• cytotoxic T cells

  • identifying abnormal or virally-infected cells
  • attach to cell and release perforin
  • perforin destroys cell by forming holes in cell membrane
• T regular cells

  • down-regulate the immune system once pathogen is destroyed
  • ensure that body does not attack self-antigens
  • reduce the chances of autoimmune disorders
• immune response

  A) pathogen

  B) non-self antigens

  C) antibody

  
• what is a capsid?

  protein coat around the core
• what are the attachemnt proteins on a virus?

  attatchemnt proteins stick out from the edge of the capsid of enevelope, let the virus cling on to a suitable host cell.
• what is the envelope on a virus?

  extra outer layer stolen from the cell membrane of a previous host cell.
• describe the structure of a virus?

  a strand of nucleic acid (DNA or RNA) enclosed within a protein coat.
• what is an antigen?

  a molecule which can trigger an immune response
• what is pahgocytosis?

  when foreign cells are engulfed by pahgocytes, digested by lyzozymes released by lysosomes in the cell.
• how does phagocytes use chemotaxis?

  phagocytes are attracted to pathogens by chemicals released by the pathogen. the phacogytes move down a concentration gradient.
• what is a lysozyme?

  mucosal surfaces produce secretions that contain lysozyme. it kills bacteria by damaging their cell walls making them burst open.
• specific immune response:

  1. cell-mediated response- involves specialised white blood cells called T-lymphocytes which target pathogens inside and outside cells
  2. humoral response- involves specialised white blood cells called B-lymphocytes which target pathogens by producing antibodies.