Primary non - specific defences in animals

• Physical barriers to infection include:

  • Skin is a tough physical barrier consisting of keratin

  • Stomach acid (hydrochloric acid) which kills bacteria

  • Gut and skin flora – natural bacterial flora compete with pathogens for food and space
• Non-specific responses:

  Inflammation – histamines released by mast cells in injured tissue cause vasodilation which increases the flow of blood to the infected area and increases permeability of blood vessels. As a result of that antibodies, white blood cells and plasma leak out into the infected tissue and destroy the pathogen
• Non - specific responses:

  • Lysozyme action – lysozyme is an enzyme found in secretions such as tears and mucus which kills bacterial cells by damaging their cell wall
• Non - specific response:

  • Interferon – interferons prevent viruses spreading to uninfected cells by stopping protein synthesis in viruses
• Non - specific response:

  • Phagocytosis is a process in which white blood cells engulf pathogens thus destroying them by fusing a pathogen such as bacteria enclosed in a phagocytic vacuole with a lysosome
• Non - specific response:

  • Blood clotting which reduces the blood loss by temporarily sealing the opening thus preventing entry of pathogens
• After the pathogen is engulfed and destroyed, its chemical markers called antigens are then presented on the surface of the phagocyte. The phagocyte then becomes an antigen presenting cell which activates other types of immune cells, immune response will be stimulated if the antigen is recognised as foreign
• The specific immune response is antigen specific and produces responses specific to one type of pathogen only
• This type of immune response relies on lymphocytes produced in the bone marrow:

  • B cells
  • T cells
• B cells mature in the bone marrow and are involved in the humoral response
• T cells move from the bone marrow to the thymus gland where they mature, they are involved in cell mediated response
• Specific immune response:

  • Memory cells are cells which replicate themselves when exposed to an invading pathogen and remain in the lymph nodes searching for the same antigen thus resulting in a much faster immune response

  • B effector/plasma cells are antibody producing cells

  • T helper cells stimulate B cells and T killer cells to divide

  • T killer cells destroy pathogen infected cells