The Immune System

1. The Immune System Year 9 Science The Body At War

2. The Battle Lines are drawn • There are billions of microbes, such as viruses and bacteria all around us. • Some of these microbes are pathogens (recall what that means?) • If given the chance, they will invade our bodies because we offer a warm place full of nutrients that allow them to grow and multiply • This can cause us to get sick

3. First Line of Defense Our best defense is to keep these pathogens out to start with. Some of our first line defenses are: • The skin– physical barrier and microbes living on our skin kill any unknown invaders • Mucous/fluids in our mouth, nose, etc. traps invading particles • Cilia– tiny hairs line our noses and respiratory tracts to remove particles

4. Second Line of Defense Sometimes, the pathogens are able to penetrate our bodies through our mouth or an open cut. Then we have additional weapons at our disposal • Stomach acid – our stomach juices are an unfriendly place for most living things and can kill many invading pathogens • Inflammation– bacteria can enter our bodies easily through a cut. Dying cells sound the alarm and defensive cells respond to the area through increased blood flow.

5. The Immune Response (3rd Line of Defense) When the first lines of defense don’t work, we have an army of cells that work to kill the invaders White Blood Cells Needed to Defend the Body Today! • Sign up now if you are a: • Phagocytes (eaters) • Granulocytes • Macrophages • Lymphocyte • T-cells • B-cells

6. Phagocytes (the eaters) Granulocytes Macrophages These white blood cells are the “big” (macro) “eaters” (phage). They are slower to respond, but are longer –lived. These cells patrol the blood stream looking for unfamiliar cells which they engulf (eat) • These white blood cells are the first responders to an attack, such as in a cut. • These cells “eat” invaders until they themselves die. • The pus of a wound is mostly dead granulocytes These cells are made in our bone marrow

7. The Lymphatic System The parts It’s mission Storage and transportation of Lymphocytes that are used in the immune response Removal of dead cells including invaders • Thymus • Lymph nodes • Spleen • Lymph vessels

8. T-Lymphocytes T-cells mature in the Thymus. There are two types: Helper T-Cells • Activate B-cells and Killer T-Cells • When a phagocyte “presents” an antigen (protein coating of a pathogen), the Helper B-Cell is activated and ready to recognise the same pathogen through “receptors”

9. T-Lymphocytes T-cells mature in the Thymus. There are two types: Killer T-Cells • Capable of recognising infected cells due to parts of the antigen of the pathogen found on the surface of the cell • Produce toxic chemicals that destroy infected or cancerous cells in the body

10. B-Lymphocytes B-Cells work by recognising specific antigens using their receptors. When it finds a match, it is activated by a Helper T and splits into two types: Plasma Cell Memory Cell Once an invader has been in the body, these cells are able to recognise them quickly the next time When recognised, they trigger a faster immune response There are also some Memory cells produced by T-cells • Produces Y-shaped antibodies that attach to the pathogen. • This helps them to clump together to be eaten by a macrophage • Antibodies are made quickly and can also prevent viruses from invading cells and neutralise toxins released

11. Macrophages The Immune Response – a pictorial representation

12. Cool caricatures from: http://nobelprize.org/educational/medicine/immunity/immune-detail.html