IMMUNE SYSTEM Viruses bacteria and other germs are

IMMUNE SYSTEM • Viruses, bacteria and other germs are all around us. Most of the time, a healthy immune system keeps us well. • The purpose of the immune system is to keep infectious micro-organisms, such as certain bacteria, viruses, and fungi, out of the body, and to destroy any infectious micro-organisms that do invade the body.

• The immune system is made up of a complex and vital network of cells and organs that protect the body from infection. • The organs involved with the immune system are called the lymphoid organs. They release lymphocytes (a certain type of white blood cell).

What are lymphocytes? • Lymphocytes - a type of infection-fighting white blood cell and are vital to an effective immune system. Lymphocytes "patrol" the body for infectious micro-organisms. • Certain cells will become lymphocytes others phagocytes. Once the lymphocytes are formed, some will mature and become "B" cells others will finish their maturation and become "T" cells.

First Line of Defence: SKIN • The Body's most important Non-specific Defence is the SKIN. Unbroken Skin provides a continuous layer that protects almost the whole body. Very Few Pathogens can penetrate the layers of dead cells at the skin's surface. • Oil and sweat glands at the surface of the skin produce a salty and acidic environment that kills many bacteria and other micro-organisms. .

First Line of Defence: Mucus, Cilia and Hairs • HAIRS -FILTER microbes and dust in nose. • MUCOUS MEMBRANES are Epithelial Tissues that protect the interior surfaces of the body that may be exposed to pathogens. • Mucous membranes serve as a barrier and secret MUCUS, a sticky fluid that traps pathogens. • Many secretions of the body, including mucus, saliva, sweat, and tears, contain LYSOZYME, an enzyme that breaks down the cell wall of many bacteria. • MUCUS, CILIA, and HAIRS in the Nose and Throat trap Viruses and Bacteria. Cilia in the Trachea trap Bacteria, Pathogens that make it to the Stomach, which are then destroyed by Stomach Acid and Digestive Enzymes.

The Second Line Of Defence: THE INFLAMMATORY RESPONSE • Despite the initial Defences of the Skin and Mucous Membranes, Pathogens sometimes enter the Body. • When Pathogens enter the Body, The Body's Second Line of Defence acts when tissues are Injured. • The injured cells release a Chemical called HISTAMINE, which starts a series of changes called the Inflammatory Response.

• The inflammatory response is a non-specific defence reaction of the body to tissue damage. • Histamine increases blood flow to the injured area and increases the permeability of the surrounding capillaries, as a result, Fluid and White Blood Cells (WBC) to leak from blood vessels into nearby tissue. • Pathogens are attacked by phagocytes, which are white blood cells that engulf and destroy pathogens by phagocytosis.

How Our Bodies Fight Disease • White blood cells: defend against germs • The immune system is made up of many different kinds of white blood cells. White blood cells work together to protect us against disease-causing germs

MACROPHAGES • Macrophages identify germs: When a germ invades our bodies, macrophages gobble up the germ and display its surface shape, or antigen, for other immune cells to see.

HELPER T CELLS • Helper T cells: direct the defence. • Helper T cells spot the foreign antigen on the macrophage and begin to multiply. They alert other white blood cells and direct the body's defence.

B CELLS • B cells: make antibodies • B cells start to make chemicals called antibodies. Antibodies lock onto foreign antigens making it easier for other immune cells to destroy them

KILLER T CELLS Killer T cells: destroy germs Alerted by helper T cells, killer T cells multiply and destroy the invading germs. Working together, our white blood cells can usually destroy invading germs

IMMUNITY • Not only does the immune system provide protection from infection through natural barriers, but it also adapts itself to provide immunity against infection by "remembering" the infectious microorganism from a previous exposure. • The degree and duration of immunity depend on the type and amount of antigen and how it enters the body.

Natural Immunity Acquired Immunity • Is created by the • Or active immunity: Develops body's natural through exposure to specific barriers, such as the foreign micro-organisms, skin, and protective toxins, and/or foreign tissues), substances in the which are "remembered" by mouth, the urinary the body's immune system. tract, and on the eye When that antigen enters the surface. Another type body again, the immune of natural immunity is system "remembers" exactly in the form of how to respond to it. When antibodies passed on that same person is exposed from mother to child. again the immune system triggers antibodies to fight the disease.

VACCINES • All types of vaccine stimulate the body's own immune system to produce antibodies and cells in the same way as the disease would but without the dangers of the disease.

Vaccines can be made up of: • Killed bacteria. • Weakened viruses or bacteria. • Parts of the bacterium or virus. • Inactivated (harmless) toxins. • Vaccines are given at a young age to protect against diseases. • Following the introduction of vaccination there has been a dramatic decrease in childhood deaths and an increase in life expectancy. • Each year vaccines prevent up to three million deaths [worldwide] and 750, 000 children are saved from disability"

HIV • To become infected with HIV, one or more virus particles must enter the body • Once inside the body they need to find their way to susceptible cells, where the HIV life-cycle begins. • T cells are the main cells which HIV targets and infects but they also target macrophages.

• The first step of the HIV life cycle is binding to the cell membrane. • Followed by membrane fusion, to get the virus particle's contents into the host cell. • Then follows reverse transcription of the HIV's genome from RNA into DNA, and its integration into the host genome. • Once integrated the virus can lie low or can begin the production of new viral RNA, turning the cell into a HIV factory • This is followed by assembly, budding, and maturation • Then the new HIV particles are packaged up and sent out to infect new cells.