Unit 4 - Immunology and Public Health CfE Higher Human Biology Non-Specific Defences

Learning Intentions I can describe non-specific defences. I can describe physical and chemical defences. Epithelial cells form a physical barrier and produce secretions against infection. I can describe the inflammatory response which 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. I can describe the structure of Phagocytes and apoptosis by natural killer (NK) cells. I can state that Phagocytes and NK 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. I can describe specific cellular defences. I can describe immune surveillance as a range of white blood cells constantly circulate monitoring the tissues. If tissues become damaged or invaded, cells release cytokines which increase blood flow resulting in specific white blood cells accumulating at the site of infection or tissue damage.

First Line Defences. The body defends itself against disease causing organisms (pathogens), some toxins, and cancer cells by using its immune system. This can be in the form of a physical defence or a chemical defence. Immunity is the ability of the body to resist infection by a pathogen or to destroy the organism if it succeeds in invading and infecting the body.

First line of defence of the body. Is Non-specific. Skin acts as a physical barrier to keep out germs/microbes. Stomach acid made by the epithelial lining of the stomach destroys the microbes swallowed Mucus in trachea traps microorganisms –the epithelial cells lining the trachea are ciliated and sweep the mucus up and away from the lungs. Tears and saliva have an enzyme called lysozyme that digests the cell walls of bacteria and destroys them.

Epithelial cells – Physical Defence Epithelial cells are our first line of defence against infection. They line the surfaces and cavities of the entire body. Form a physical barrier against infection.

These cells cover almost the entire surface of the body. They grow constantly upwards and outwards from the bottom layer and by around 14 days they have become dead cells called stratum corneum which flake off taking any bacteria or pathogens with them. Epithelial cells also produce secretions such as enzymes, hormones and lubricating fluids that can defend against infection.

Secretions – Chemical Defences On all the inside surfaces of the body that can be exposed to bacteria and pathogens a substance called mucus traps dirt and germs, preventing them from entering the blood. Various glands produce antimicrobial secretions that help kill microbes.

Other defences Tiny hairs at the entrance to the nose. Cough and sneeze reflexes. ‘Friendly’ bacteria.

The Inflammatory Response-mast cells(second line of defence). Chilblains – inflammation of the toes (or other extremities) caused by prolonged exposure to moisture and cold. Acne – inflammation of the skin caused by bacteria in the pores Inflammation is a common response to bee/wasp stings Tonsillitis – inflammation of the tonsils

Inflammatory response-mast cells(second line of defence). This operates when the body suffers a physical injury or invasion by microbes. Following injury mast cells are activated and release large amounts of histamine which is a chemical that dilates blood vessels that lets them fill up with blood. Mast cells are made from the same stem cells that make white blood cells and are found in connective tissue throughout the body. Blood vessels in the injured area vasodilate and fill full of blood which makes the area swollen, red and inflamed. The tissues become swollen because the capillaries become more permeable and tissue fluid leaks out.

Non-specific inflammation The inflammatory response is triggered when something breaks the skin.

Cytokines attract white blood cells called phagocytes to the area and the release of antimicrobial proteins or clotting elements to the damaged area. Histamines are also released which cause the capillary to vasodilate and become more permeable. Look at the following animation: Video

Self or non-self? N5 revision On the surface of a cell membrane, there are many proteins partially embedded in the lipid bilayer. Some of these proteins are called antigens and allow our immune system to recognise our own cells. Invading bacteria and viruses which would cause disease (pathogens) have different antigens – non-self. Destroying invading pathogens

Phagocytes Once the bacterium is inside the phagocyte, lysosomes fuse with the vesicle, digesting the bacterium. VIDEO Phagocytes are cells which will engulf and digest a foreign particle such as bacteria. They recognise the foreign antigen molecules on its surface then bind with the bacterium and engulf it by endocytosis.

Non-specific cellular responses-phagocytosis (second line of defence). The process of phagocytosis is carried out by a type of white blood cell called a phagocyte. Phagocytes can move and when they detect chemicals released by a pathogen or detect antigens present on the surface of a pathogen they move towards it. The pathogen is engulfed(taken in to the cell) and the cell membrane folds in to form a vacuole with the pathogen inside it. Lysosomes which are vesicles filled with digestive enzymes fuse with the vacuole and release their digestive enzymes into it. The pathogen is broken down and the products are absorbed by the phagocyte. Cytokines are released by the phagocyte and they attract more phagocytes to continue the battle. pus is dead bacteria and phagocytes that can form at a site of injury.

Natural killer cells Natural killer (NK) cells are found in the blood and are constantly looking for signs of an infection. They can also release cytokines but they have an important role in destroying a pathogen-infected cell. They look for a cell which has not got the normal surface antigens or self antigens and knows that it must be infected. It then destroys it with self-destructive enzymes perforating the plasma membrane, bursting it, a process called apoptosis.

Non-specific cellular responses-natural killer cells(second line of defence) NK cells are not phagocytic. They attack virus-infected cells in general and cancer cells. The NK cells releases molecules of a protein which forms pores in the target cells of the membrane. Signal molecules from the NK cell can then enter the target cell and trigger a genetically controlled series of events. The target cell produces cell destructive enzymes and the cell’s DNA and vital proteins are broken down and destroyed and the cell dies. This is called a programme of cell death and is called apoptosis.

Cytokines. NK cells and phagocytes also release cytokines after contact with a pathogen. These molecules move in the blood and stimulate the specific immune response by activating lymphocytes.

Inflammatory response-cytokines (in non-specific and specific defences ). These are very important chemicals involved in this response. They are called cell signalling protein molecules and can be made by many types of cells including white blood cells that have arrived at an injury. During the inflammatory response increased blood flow and permeability of capillary walls at site of injury bring about the following effects to help: 1.Cytokines attract more phagocytes to the damages tissue and these engulf pathogens by phagocytosis and clean up the injured site. 2.Fast delivery of anti-microbial proteins to the infected site which amplify the immune system. 3.Rapid delivery of blood clotting chemicals to the injured site to prevent other microbes entering and to start repair.

Questions 1.Name a secretion made by the epithelial cells lining the inside of the body. 2.What name is given to the immediate response of the body to a cut? 3.What are mast cells? 4.Why do the capillaries vasodilate? 5.What general name do we give disease-causing organisms? 6.Describe what an antigen is made of and where it is found. 7.What is the name of the cell signalling molecule produced by many immune cells?

Questions 8.Describe the process of phagocytosis. 9.What are NK cells? 10.Describe the stages involved in apoptosis.

Answers 1.Name a secretion made by the epithelial cells lining the inside of the body. - Mucus 2.What name is given to the immediate response of the body to a cut? - Inflammatory response 3.What are mast cells? - Cells found under the epithelium containing histamines and cytokines 4.Why do the capillaries vasodilate? - Histamines causes this 5.What general name do we give disease-causing organisms? - Pathogens 6.Describe what an antigen is made of and where it is found. - An antigen is a protein marker found on the cell membrane surface 7.What is the name of the cell signalling molecule produced by many immune cells? - Cytokine

Answers 8.Describe the process of phagocytosis. Phagocyte recognises antigen on surface of pathogen as ‘non self’ Phagocyte attaches to antigen Phagocyte engulf pathogen into vacuole/vesicle Lysosomes containing digestive enzymes bind with vacuole/vesicle. Pathogen digested 9. What are NK cells? - Natural Killer Cells which recognise damaged or cancerous cells 10. Describe the stages involved in apoptosis ( cell death ) NK cell produces protein which punctures cell membrane of cell NK protein binds to ‘suicide gene’ in nucleus of cell Proteins produced by ‘suicide gene’ destroy cell

Glossary Epithelial cells Inflammatory response Pathogen Antigen Non-self Mast cells Histamines Cytokines Vasodilation Permeability Phagocytes Lysosomes Natural killer cells Apoptosis