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Transcript
The Immune System Immunity = the body’s ability to resist infection can be natural or acquired Pathogens disease causing microorganisms bacteria virus fungi, protozoa, parasite, allergens Three Lines of Defense How does the body fight infection/foreign invaders? The Body has 3 lines of Defense First Line of Defense – The Skin • Provides Physical and Chemical barriers Physical – hard to penetrate, made of indigestible keratin Chemical – tears, sweat First lines of defense saliva antibacterial enzymes (lysozymes) skin prevents entry, bacteria stomach acid low pH kills harmful microbes tears antibacterial enzymes (lysozymes) mucus linings, cilia traps dirt and microbes Bacterial flora - out compete bad Second Line of Defense – Nonspecific Immune Response Includes: Phagocytosis – done by Macrophages (neutrophils and monocytes) Natural Killer Cells (NK) – secretes perforins (cytolitic) Inflammation - caused by release of Histamine from leukocytes Fever – caused by histamines and pyrogens. The fever (high temp) kills invaders and decreases their growth by denaturing their proteins. Phagocytes Phagocytes Monocytes and macrophages Provide a non-specific response to infection http://www.microbelibrary.org/imag es/tterry/anim/phago053.html Phagocytosis Pus An accumulation of : dead phagocytes destroyed bacteria dead cells Third Line of Defense Specific response – (Immunity) lymphocytes produce antibodies that target specific pathogens Lymphocyte Lymphocytes Provide a specific immune response to infectious diseases. 2 types: - T-cells –mature in thymus - B-cells mature in bone marrow then are found in lymph nodes and spleen They circulate in blood and lymph and produce antibodies. Antigens all cells have surface markers called antigens. Large and complex proteins, polysaccharides, glycoproteins, or glycolipids body can recognize these as self or nonself (foreign) Specific response Lymphocytes detect presence of foreign antigens Stimulated to produce specific proteins called antibodies. How an antibody works? Deactivation of a bacterium by an antibody = primary response. Macrophages – Antigen presenting cells (APCs) Antigen becomes part of the MHC (major histocompatibility complex)/HLA (human leukocyte antigens) *Used for transplant compatibility. The Pathway of Specific Immune Response Step 1 Pathogens eaten by Macrophage Step 2 Displays portion of Pathogen on surface Step 3 Pathogens Helper-T cell recognizes Pathogen T-Lymphocytes have receptors with similar structure to antibodies and are specific to 1 antigen. activated when the receptor comes into contact with the antigen with another host cell (e.g. on an APC) T-Lymphocytes After activation the cell divides to form: Helper T cells – secrete CYTOKINES help B cells divide and produce antibodies stimulates macrophages Activates cytotoxic T cells Cytotoxic T cells (killer T cells) Kill body cells displaying antigen Bind to APC and release perforins Memory T cells clones that remain in body for future immunity B –Lymphocytes (humoral/fluid response, antibody-mediated) 10 million different B-lymphocytes, each make a different antibody Receptors in the membrane recognize the antigen on the surface of the pathogen or APC, cytokines released by helper T cells the activated B-cell divides rapidly. B -Lymphocytes Some activated B cells PLASMA CELLS and produce lots of antibodies, ~ 1000/sec The antibodies travel to the blood, lymph, lining of gut and lungs. The number of plasma cells goes down after a few weeks Antibodies stay in the blood longer but eventually their numbers go down too. B -Lymphocytes Some activated B cells MEMORY CELLS. Memory cells divide rapidly as soon as the antigen is reintroduced. There are many more memory cells than there were clone cells. When the pathogen/infection infects again it is destroyed before any symptoms show. Activates Cytotoxic Cytokines! Activates B- Cell T- Cell perforins Memory T-Cell Kills Infected Memory B-Cell Antibodies Cellular Immunity .vs. Antibody Immunity Cellular Immunity Carried out by TCells Infected cells are killed by Cytotoxic T –Cells. Antibody or Humoral Immunity Carried out by Bcells Antibodies are produced and dumped into blood stream. Antibodies bind to antigens and deactivate them. Immune Response Explained 1. 2. 3. 4. 5. 6. 7. 8. 9. Antigen infects cells. Macrophage ingests antigen and displays portion on its surface. Helper T- Cell recognizes antigen on the surface of the macrophage and becomes active. Active Helper T-Cell activates Cytotoxic T-Cells and BCells. Cytotoxic T-Cells divide into Active Cytotoxic T-cells and Memory T – Cells. Active Cytotoxic T-Cells kill infected cells. At the same time, B-Cells divide into Plasma Cells and Memory B- Cells. Plasma cells produce antibodies that deactivate pathogen. Memory T and Memory B cells remain in the body to speed up the response if the same antigen reappears. Immune Response Summary Displays copy of antigen on surface of cell Antigen Macrophage Cellular Immunity Helper T - Cell Active Cytotoxic T-Cell Kills Infected Cells Memory T- Cell Antibody Immunity Active B - Cell Plasma Cell Antibodies Deactivates Antigens Memory B-Cell Primary .vs. Secondary Immune Response Primary Immune Response This is a response to an invader the First time the invader infects the body. No measurable immune response for first few days. Next 10 – 15 days antibody production grows steadily Secondary Immune Response A more rapid response to an invader the 2nd time it invades the body. Antibody production increases dramatically and in a much shorter time period.. Antibodies Also known as immunoglobulins Globular glycoproteins The heavy and light chains are polypeptides held together by disulphide bridges The order of amino acids in the variable region determines the shape of the binding site - variable How Abs work Some act as labels to identify antigens for phagocytes Some attach to bacterial flagella making them less active and easier for phagocytes to engulf Some cause agglutination (clumping together) of bacteria making them less likely to spread Increase inflammation to prevent spread Different Immunoglobulins Type Number of ag binding sites Site of action Functions IgG 2 •Blood •Tissue fluid •can cross placenta •Increase macrophage activity •Antitoxins •Agglutination (antiRh) IgM 10 •Blood •Tissue fluid Agglutination Ex-food antigens IgA 2 or 4 •Secretions (saliva, tears, small intestine, vaginal, prostate, nasal, breast milk) •Stop bacteria adhering to host cells •Prevents bacteria forming colonies on mucous membranes IgE 2 Tissues •Activate mast cells HISTAMINE •Worm and allergy Immunological memory after an infection is fought off some lymphocytes become memory cells. if same pathogen returns memory cells stimulate the produce the specific antibody very rapidly. the infection is fought off before symptoms appear = secondary response vaccines can stimulate same response Primary .vs. Secondary Immune Response Passive .vs. Active Immunity 1. Active Immunity This is immunity where the body is “actively” producing antibodies to fight infection. Ex: You have a throat infection and you are actively creating antibodies to fight it. Vaccination: An injection of a weakened strain of an infectious microbe (pathogen) that causes the body to undergo active immunity (produce antibodies). 2. Passive Immunity This is immunity where antibodies are given to a person from the blood of another person or animal. This immunity only lasts for a short period of time. ex: Breastfeeding mothers pass antibodies to their children through the milk. Vaccination A preparation containing antigenic material: Whole live microorganism Dead microorganism Attenuated (harmless) microorganism Toxoid (harmless form of toxin) Preparation of harmless antigens Allergies When the immune system responds to harmless substances Allergens – antigenic substances which do no real harm Allergens include house dust, animal skin, pollen, house dust mite and its faeces There are two types of allergic reactions. a. Immediate – occurs within seconds and normally lasts for about 30 mins. b. Delayed – takes longer to react and can last for a much longer time. What happens during an allergic reaction? During an allergic reaction antibodies cause histamines to be released from certain cells. Histamines cause: a. Swelling of tissues b. Release of fluids (runny noses and eyes) c. Muscle spasms (some cases) Example: TB (Mantoux test) Allergies Histamine causes blood vessels to widen and become leaky. Fluid and white blood cells leave capillaries. The area of leakage becomes hot, red and inflamed Anaphylaxis or anaphylactic shock: This is the sudden and severe allergic reaction to a substance that can cause death. -inherited tendency to over-produce IgE (evolved to protect against round and flat worm infection) Treatments for Allergies 1. Avoidance of material – especially food. 2. Epinephrine – “epi – pen” 3. Antihistamines -- benadryl Autoimmune Disease Autoimmune diseases are diseases where the immune system begins to attack itself. Ex: Rheumatoid Arthritis – crippling disease of the joints. Lupus – disease of blood and organs. Multiple Sclerosis – disease of nervous system Cause(s): mostly unknown; virus alters proteins,T cells don’t differentiate properly; a nonself may resemble a self antigen More common in females –fetal cells transport through circulation and cause later response Cures/Treatments: No known cures. Usually treated with drugs.