 The system that keeps us alive and healthy – we call it the immune system.  Pathogens – microorganisms that produce diseases in us. (Bacteria, viruses, fungi, and parasites.  Lymphocytes – The cells of the lymphatic system that respond to ◦ Invading pathogens ◦ Abnormal body cells (ex. Cancer) ◦ Foreign proteins (ex. Toxins)

 Vessels – a network throughout the body  Fluid – called lymph  Lymphoid Organs – contain a large number of lymphocytes (example Lymph and spleen)

 T-Cells (thymus-dependent) ◦ 80% of all lymphocytes ◦ Cytoxic attack foreign and infected cells ◦ Helper T-Cells – send a signal for more or less T- cells or B-cells  B-Cells (bone marrow derived) ◦ 10-15% of all lymphocytes ◦ Differentiate into plasma cells which secrete antibodies which react to the antigens (pathogen or part of a pathogen)

 NK Cells (Natural Killer cells) ◦ 5 – 10% of all lymphocytes ◦ Attack normal cells infected with viruses or foreign cells. ◦ Lymphocytes travel throughout your system. Most of them live for 4 years. Some can live for 20 years or more!

 Hemoctyoblasts ◦ Produce lymphoid stem cells ◦ Some remain in the bone marrow to make b-cells and NK cells  Lymphoid Organs ◦ Lymph Nodes  Filter and purify lymph  Located in regions where they can detect and eliminate harmful intruders before they reach vital organs.

 Thymus ◦ T-cell maturation occurs here (located behind the sternum) ◦ 2 parts  Cortex – where T-cells divide and mature  Medulla – where mature T-cells go in preparation to enter the blood stream.

 Spleen ◦ In between stomach and left kidney ◦ Blood flows through the spleen macrophages, identify and engulf any damaged or infected cells. ◦ Any abnormal antigens (pathogens) will produce an immune response. Lymph doesn’t affect cancer so that is typically the system that cancer uses to spread throughout the body (through the lymph glands)

 Your body has two types of defenses  Nonspecific  Specific  Nonspecific Defenses: ◦ Present at birth ◦ Physical barriers  Epithelium (skin)  Hair  Cilia  Mucus  Digestive Juices

 Phagocytes ◦ Microphages are found in the blood, when an injury occurs they enter infected areas and basically eat pathogens ◦ Macrophages are found all over the body and are derived from monocytes in the blood. They are sensitive to chemicals released by foreign bodies. They work throughout your body eating pathogens before they can do harm to you.

 Immunological Surveillance ◦ NK cells identify cancer cells and cells that are infected with a virus  Complement ◦ Complement activation is when a protein in your body binds to the pathogen. This causes:  Attraction to phagocytes  Enhances phagocytosis  Destroys cell membranes  Promotes Inflammation

 Inflammation ◦ Results in swelling, redness, heat and pain ◦ Mast cells release chemicals that cause:  Blood flow increase  Phagocytes are activated  Capillary permeability increases  Complement is activated  Clotting reaction walls off region  Regional temperature is increased  Specific defenses are activated.

 Fever ◦ Caused when the hypothalamus is influenced by the presence of pyrogens released by toxins or antibody-antigen complexes ◦ Higher temperature speed up immune system. (104 or higher can be dangerous to you with CNS problems)

 Provides immunity  Specific to each pathogen  Requires T-cells and B-cells  3 forms of immunity: ◦ Innate Immunity – genetically determined  People not subject to diseases same as goldfish or dogs ◦ Active Immunity – When antigens are present they stimulate the production of antibodies. These antibodies are specific to diseases. We also produce antibodies through controlled vaccinations.  This is when we get sick

 Passive Immunity – when we acquire immunity through someone or something else. This would either be mother to child (through the placenta) or by taking antibodies to fight infection or diseases.

 Specificity – each disease has its own antigen recognition.  Versatility – The immune system has to be ready for any infection. It can produce an appropriate and specific response to each antigen.  Memory – Our immune system remembers specific antigens. Therefore, if our body recognizes the same antigen again it can produce a faster and stronger attack.  Tolerance – Our immune system has a tolerance for our antigens. It doesn’t allow normal tissue to be attacked.

 T-Cells are activated by the presence of an antigen. This can occur by antigen- lymphocyte interaction. However, typically a receptor called the Major Histocompatibility Complex (MHC) is responsible.  How does MHC work? ◦ Macrophages eat the pathogens, break them down and send out recognition antigens. When a cells MHC comes in contact with the macrophage they then can display the antigen on their cell surface which will initiate an immune response.

 Coordinate specific and non-specific defenses.  Stimulate cell mediated immunity and antibody-mediated immunity.  These are the cells affected in the disease of AIDS. The body doesn’t produce an immune response because these cells aren’t working.

 Helper T-Cells bind to inactive B-cells and cytotoxins.  Stimulates B-cell activation.  Stimulates B-cell division (some go on to plasma cells and some remain as memory B-cells)  Accelerates Plasma cell production  Antibodies are created.  Memory B-cells act the same as Memory T-cells. If the same pathogen is in the body they recognize it and immediately turn to plasma cells which create antibodies.

 Antibodies are also called immunoglobulins  IgG – Responsible for defense against many viruses, bacteria and bacterial toxins  IgM – Responsible for reactions to incompatible blood types.  IgA – Attack pathogens before they enter the body tissues.  IgE – Accelerates inflammation based on exposure to antigens  IgD – Binds antigens to B-Cells

 Neutralization – Antibodies bind to toxins or viruses making them inactive.  Agglutination and Precipitation – Several antibodies bind to the same pathogen and form a clump (cell agglutinate or come together) and then precipitate out of the blood system.  Activation of Compliment – The antibody binds to the antigen and it changes the shape, which destroys the pathogen.

 Attraction of Phagocytes – Binding causes phagocytes to recognize the intruder.  Enhancement of Phagocytes – binding makes the phagocytes more effective.  Stimulation of Inflammation – slows the spread of infection.

 Autoimmune Disorders – The body attacks itself.  Immunodeficiency disorders – The immune system fails to develop or is blocked in some way.  Allergies – caused by antigens called allergens.