Infectious Diseases and the Immune System “What doesn’t kill you makes you stronger.”
Types of pathogens • Bacteria: single cell organism World's Dirtiest Man 2. Virus: not alive, one or more molecules of DNA or RNA enclosed in a protein capsule. 3. Protists: usually single celled organisms without specialized tissues. Giardia 4. Fungi: ringworm, yeasts 5. Invertebrates: parasitic worms
Modes of Disease Transmission 1. Air: tuberculosis, cold 2. Food: Salmonella, E. coli, botulism 3. Water: Giardia 4. Person-to-person: (cold, hepatitis, HIV) 5. Vectors - animal bites/scratches/burrowing: (malaria/lyme disease)
Koch’s Postulates • The suspected pathogen must occur in the body of an animal with the disease but NOT in the body of a healthy animal.
Koch’s Postulates • The suspected pathogen should be isolated, identified, and grown in a laboratory culture.
Koch’s Postulates • If a healthy animal is inoculated with the cultured pathogen, it should develop the disease.
Koch’s Postulates • If the pathogen from the second animal is isolated and grown in the lab, and identified as the same one isolated from the first animal, that confirms this pathogen as the cause of this particular disease.
Nonspecific Defenses • Protect against any pathogen regardless of identity
First Line of Defense • Physical barriers – skin, mucous membranes • Skin • tough, keratin-filled cells • Secretes oils & waxes (sebum) toxic to bacteria & fungi • Sweat (and tears) contains lysozyme, destroys cell walls of bacteria • very effective if not broken
Mucous Membranes • Line all interior surfaces exposed to environment • respiratory system (works w/cilia) • digestive system • urethra • Vagina • Sticky mucus traps pathogens • Stomach acid & enzymes destroy many pathogens
Second Line of Defense 1. Inflammatory response – redness, swelling, warmth, pain • Pathogens stimulate special WBC called mast cells to release histamine. • Histamine dilates blood vessels & increases blood flow to the area. May also increase mucous production. • Histamine also increases permeability of capillaries to fluids & white blood cells (WBC), accumulate as pus.
Second Line of Defense • White Blood Cells – WBCs involved in inflammatory response are called phagocytes(phage = “to eat”). Phagocytosis = eats cells. • Neutrophils: 50-70% of all WBCs – each engulfs & destroys a pathogen, neutrophil also dies in the process. • Macrophages: travel in blood, lymph, intercellular fluids, engulf & destroys pathogens, worn out cells, & cell debris. Long-lived. • Natural Killer Cells – seek & destroy cancer cells and cells invaded by pathogens (viruses). Punctures cell membrane, water rushes in, cell bursts.
Second Line of Defense • Nonspecific Immune Proteins • Complement system – 20 proteins that enhance (“complement”) the ability of antibodies & phagocytes to clear pathogens from body. Activates MAC. • MAC – membrane attack complex – forms channels across cell membranes of pathogens, causes cell lysis(bursting) and death.
Nonspecific Immune Proteins C) Interferon– inhibit (“interfered” with) reproduction of viruses. Released by infected cells, stimulates nearby cells to make enzyme that inhibits synthesis of viral proteins. Buys time for specific immune response.
Second Lind of Defense • Fever – body temp. (controlled by hypothalmus in brain) above 98.6o F (37o C). Body attempts to “cook” proteins of pathogens without cooking its own. Fever above 103o F is dangerous, over 105o F can be fatal.
Third Line of Defense • Specific Immunity – immune system targets specific pathogens • Pathogens identified by the antigens on their surfaces.
Organs of the Immune System • Red bone marrow • Thymus • Lymph nodes • Spleen • Tonsils • Adenoid • Peyer’s patches
Organs of the Immune System Red bone marrow makes stem cells that differentiate to form neutrophils, macrophages, natural killer cells, and lymphocytes.
Organs of the Immune System Thymus – some immature lymphocytes migrate to the thymus and mature there. These are called T cells. There are 3 kinds: • Helper T cells • Suppressor T cells • Cytotoxic T cells Other lymphocytes remain in the bone marrow to mature. These are B cells.
Organs of the Immune System Lymph nodes – • populated by lymphocytes and macrophages • filter lymph looking for foreign antigens, worn out cells, or cellular debris
Organs of the Immune System Spleen – circulatory system’s counterpart to lymph nodes. • Located behind stomach • Filters pathogens from blood.
Organs of the Immune System • Adenoids – located on either side of the throat near the roof of the mouth • Tonsils - located below & behind soft palate. • Both are cluster of lymphatic tissue that intercept inhaled germs and dust & initiate B & T cell responses.
Organs of the Immune System Peyer’s Patches – • Lymphatic tissue embedded in the walls of the small intestine. • intercept pathogens not destroyed by the stomach.
Third Line of Defense – Specific Immunity, Primary Immune Response How it works: • Macrophage encounters & engulfs pathogen. • Macrophage displays antigens of pathogen on its own cell membrane. • Macrophage connects with a Helper T Cell with a receptor matching the antigen. This stimulates the Macrophage to produce Interleukin-1.
Third Line of Defense – Specific Immunity, Primary Immune Response • Interleukin-1 stimulates Helper T cell to produce Interleukin-2. • Interleukin-2 stimulates four different populations of cells: a. Helper T Cell itself, to divide into clones. b. Cytotoxic T Cells c. B Cells d. Suppressor T Cells
Third Line of Defense – Specific Immunity, Primary Immune Response Cytotoxic T Cells: • Stimulated • Rapidlydivide into army of cells programmed to find and destroy the specific pathogen, infected cells, or cancer cells of the pathogen first encountered by the macrophage. • Recognize infected cells by viral proteins on the cell surfaceor antigens on cancer cells. • This is Cell-Mediated Immune Response.
Third Line of Defense – Specific Immunity, Primary Immune Response B Cells: • stimulated • divide rapidly • differentiate into Plasma Cells, which make antibodies specific to pathogen first encountered by macrophage. • Called Humoral Immune Response.
Third Line of Defense – Specific Immunity, Primary Immune Response Antibodies • Y-shaped proteins with receptors specific for antigen of pathogen first encountered by macrophage. • Antibodies bind to pathogen, flag it for destruction by nonspecific WBCs or Cytotoxic T Cells, and may inhibit viruses from infecting cells.
Third Line of Defense – Specific Immunity, Primary Immune Response Suppressor T Cells: • Once stimulated, begin dividing, but much slower than Cytotoxic T Cells and B Cells. • Function: to shut down cell division of B Cells. • Delay gives the B Cells time to proliferate enough to deal with the infection.
Secondary Immune Response • MOST of the Cytotoxic T Cells and B Cells produced by the Primary Immune Response are relatively short-lived. • SOME are programmed to live much longer, remain in bodylong after first infection iseliminated. THESE are called Memory T Cells and Memory B Cells.
Secondary Immune Response • Memory T & B Cells patrol circulatory and lymphatic systems &organs of immune system for many years, often for life. Memory T & B cells = immunityto that pathogen. • IF they ever encounter same pathogen again, response is RAPID and STRONG. They immediately begin dividing to quickly accomplish their jobs. • Secondary immune response is so fast and efficient that person often does not even know he/she is infected.
Immunity • Immunity can be monitored by checking the level of antibodies in the blood • This level is known as the antibody titer.
Allergies • immune response to harmlessantigens (dust, pollen, etc.) – calledallergens • symptoms – cells in contact with antigen release histamine, causes runny nose, watery eyes, sneezing, itching to expel antigen from body • severe allergic reactions can include anaphylactic shock – life threatening
Autoimmune Diseases Your immune system attacks your own cells. a. Multiple sclerosis – attacks nervous system b. Type 1 diabetes – attacks insulin-producing cells of pancreas c. Lupus – attacks connective tissues d. Rheumatoid arthritis – attacks joints, causes inflammation e. Graves disease – attacks thyroid
HIV & AIDS • HIV attacks Helper T cells. • Lowered levels of Helper T cells are unable to initiate a full primary immune response. • Individual dies of an opportunistic infection, a pathogen or cancer that a healthy immune system would have defeated easily.