The Immune System

1. The Immune System Non-Specific Immunity

2. What You Should Know • The human body has the capacity to protect itself against pathogens, some toxins and cancer cells through the immune system. • Non-specific defences include physical defence as the epithelial cells form a physical barrier and chemical defences – chemicals are produced and secreted against infection. • Inflammatory response includes the release of histamine by mast cells causing vasodilation and increased capillary permeability. • The increased blood flow and secretion of cytokines leads to an accumulation of phagocytes and the delivery of antimicrobial proteins and clotting elements to the site of infection. • Phagocytes and NK (natural killer) cells release cytokines which stimulate the specific immune response. • Phagocytes recognise surface antigen molecules on pathogens and destroy them by phagocytosis. • NK cells induce the pathogen to produce self-destructive enzymes in apoptosis.

3. Non-specific Cellular Defence • The body has an immune system for defence against • pathogens • some toxins produced by living things • cancer cells • Immunity is the ability of the body to • resist infection by a pathogen • or to destroy the pathogen if it invades the body

4. Barriers defence The skin is composed of layers of epithelial cells which provide a physical barrier against bacteria and viruses Mucus membranes that line the digestive and respiratory tracts are also composed of epithelial cells First Line Defence-Non Specific

5. Chemical defence • Secretions from the skin’s sweat glands and sebaceous glands keep the pH of the skin too low for many organisms • Secretions such as tears and saliva contain lysozyme which digests bacterial cell walls killing them • Cells in mucus membranes secrete mucus which traps microorganisms • Ciliated cells in the trachea sweep mucus and trapped microbes up and away from the lungs • Acid secreted by the epithelial cells lining the stomach destroys many of the microbes which have been swallowed bacteria (yellow) sticking to the mucus (blue) on the hair-like cilia

6. Inflammatory Response • Prevents • spread of injurious agents to adjacent tissues • disposes of pathogens and dead tissue cells • promotes tissue repair

7. Mast Cells and Histamine • Histamine – • released from mast cells and promotes vasodilation of local arterioles and increased permeability of local capillaries • Signs: redness, pain, heat and swelling • Increased blood flow and permeability of capillary walls enhances the migration of phagocytes to the damaged area

8. Cytokines • Cytokines are cell signalling proteins released by phagocytes and natural killer cells when in contact with a pathogen • They are important in both non specific and specific immunity • Secreted from white blood cells at the site of injury • The increased blood flow and secretion of cytokines leads to • an accumulation of phagocytes which carry out phagocytosis • the delivery of antimicrobial proteins and clotting elements to the site of infection

10. Phagocytes • Phagocytes also release cytokines which stimulate the specific immune response by activating lymphocytes • Phagocytes recognise surface antigen molecules on the pathogens and destroy them by phagocytosis

11. Natural Killer Cells • Natural killer cells also release cytokines which stimulate the specific immune response by activating lymphocytes • NK cells attack virus infected and cancerous cells • NK cells release proteins that cause the cell to produce self-destructive enzymes resulting in cell death by apoptosis