Immunity

• 1. Phagocytes have receptors (extrinsic proteins) on the cell surface membrane that detect antigens, causing chemotaxis.
• Chemotaxis - a directional response to stimulus.
• 2. A phagosome forms to engulf the pathogen, which is then digested by hydrolytic enzymes in the lysosomes.
• (BACTERIA) Receptors (peripheral proteins) on the cell surface membrane of the phagocyte detect antigens on the bacteria, causing chemotaxis.
• (BACTERIA) The process of endocytosis forms a phagosome to engulf the bacteria, which then undergoes lysosome fusion and is digested by the hydrolytic enzymes in the lysosome.
• (BACTERIA) Exocytosis releases non-useful parts of the bacteria from the cell - antigens are retained and presented so the cell becomes an APC.
• There are two types of specific immune response: humoral and cell mediated.
• The cell-mediated response involves T cells, which are produced in the bone marrow and matured in the thymus.
• The humoral response involves B cells, which are produced and matured in the bone marrow.
• An antigen is a chemical that can trigger an immune response.
• There are 4 types of APC:

  • cancer cells
  • phagocytes
  • blood cells
  • pathogenically infected cells
• There are two types of T cell:

  • T helper cell
  • cytotoxic T cell
• Helper T cells recognise antigens, activate Tcs and stimmulate B cells to make antibodies.
• Cytotoxic T cells bind to infected cells, release enzymes (perforin) and destroy the APC by triggering cell suicide.
• Specific T helper cells that have a complementary receptor to the antigen bind to antigens on antigen-presenting phagocytes, causing them to become activated.
• Activated TH cells divide rapidly by mitosis and create clones.
• Cloned TH cells develop, stimulate phagocytosis, stimulate B cells and activate Tc cells which kill infected body cells.
• B-cell receptors bind to complementary antigens, then present them on their surface, becoming APCs.
• Clonal selection: TH cells attach to the antigen and activate the B cells.
• Clonal expansion: Activated B cells divide by mitosis, forming clones.
• Cloned B cells differentiate into plasma cells or memory cells.
• Plasma cells:

  • produce antibodies
  • primary immune response
• Memory cells:

  • divide to become plasma cells when encountering the same antigen
  • secondary immune response
• Antibodies are all proteins made of 4 polypeptide chains, demonstrating quaternary structure.