SPECIFIC DEFENSE: THE IMMUNE SYSTEM
Lymphocytes: are white blood cells that exists in two primary forms B cells: made in the bone marrow and complete their development there or in the spleen. B cells make antibodies. T cells are cells that are made in the bone marrow but complete their development only after traveling to the thymus. T cells also participate in many immune reactions.
RECOGNIZING PATHOGENS An antigen is any substance that the immune system does not recognize as part of the body. Because the lymphocytes do not recognize the antigen, they start a specific attack known as an immune response. Lymphocytes recognize a pathogen with molecules on their surface called receptor proteins. This is how the lymphocyte recognizes the antigen. Only the specific receptor protein that is complementary to the antigen will be able to bind there.
IMMUNE RESPONSE An immune response is a two-part assault on a pathogen (Cell mediated immune response and Humoral Immune response). Both parts occur at the same time and require a specialized lymphocyte called a helper T cell. T cells activate certain proteins that affect the behavior of other immune cells. These proteins are called cytokines.
CELL-MEDIATED IMMUNE RESPONSE In the cell-mediated immune response, cytokines activate more helper T cells and another type of T cell called a cytotoxic T cell. Cytotoxic T cells recognize and destroy cells that have been infected by a pathogen. Also produced during the cell-mediated immune response is a type of T cell called the suppressor T cell. Suppressor T cells are thought to shut down the immune response after the pathogen has been cleared from the body.
HOW A CYTOTOXIC T CELL RECOGNIZES AN INFECTED CELL
HUMORAL IMMUNE RESPONSE The humoral immune response involves the action of B cells and occurs when antibodies are activated within body fluids. Most B cells form plasma cells. A plasma cell is a white blood cell that produces antibodies. Antibodies are defensive proteins that react to a specific antigen or inactivate or indirectly destroy toxins.
THE IMMUNE RESPONSE
PRIMARY AND SECONDARY IMMUNE RESPONSES The first time the body encounters an antigen, the immune response is called a primary immune response. During this first encounter, the immune system fights off the disease. After the disease is overcome, the immune system creates memory cells. Memory cells are a B cell or T cell that will recognize and attack the antigen or invading cell during subsequent infections. The second time the body encounters an antigen, a secondary immune response occurs (faster & more powerful ). Most of the time, the secondary immune response protects the body from reinfection by a pathogen.
IMMUNITY AND VACCINATION Immunity is the ability to resist an infectious disease. Immunity can come about in two ways: surviving an initial infection or through vaccination. Vaccination is the introduction of antigens into the body to cause immunity.
VACCINES A vaccine is a solution that contains a dead or weakened pathogen or material from a pathogen that still contains antigens. The immune system will produce a primary immune response to the antigens. Memory cells can then provide a quick secondary immune response if the antigen ever enters the body again.
PROBLEMS OF THE IMMUNE SYSTEM Sometimes the immune system can react to harmless antigens. Three examples of this are allergies, asthma, and autoimmune diseases. Allergies allergy -a physical response to an antigen, which can be a common substance that produces little or no response in the general population.
ASTHMA Allergies can trigger asthma. Asthma is a respiratory disorder that causes the bronchioles to narrow due to an overreaction to substances in the air. During an asthma attack, the lining of the bronchioles and other respiratory tissues may also swell and become inflamed.
PROBLEMS OF THE IMMUNE SYSTEM Autoimmune Diseases An autoimmune disease occurs when the immune system attacks an organism s own cells. Autoimmune diseases can affect organs and tissues in various areas of the body.