How do your body systems protect you from infection and disease?

11.1 Defense Against Infectious Disease Learning Targets: Describe blood clotting, challenge and response, clonal selection, and memory cells. Explain the principle of vaccination.

Nonspecific Defenses: External defenses – skin and mucus membranes –Act as a barrier, trap foreign materials –Low pH (such as in stomach) and secretions (ex. lysozyme in tears) kill some pathogens

Internal defenses – phagocytic cells (white blood cells that eat invaders) –Phagocytes or macrophages may circulate or stay in one tissue – they catch microbes with long pseudopodia, and engulf pathogens

Blood Clotting –Use the video clip to put the steps in the correct order

Blood Clotting –Initiated by chemical signals released by damaged cells –Platelets adhere to the damaged area and begin to plug the opening

Blood Clotting –Tissues and platelets release chemicals that convert prothrombin to thrombin –Thrombin converts fibrinogen into fibrin which creates a supportive mesh to stabilize the clot

Why are the defenses above called nonspecific? These defenses respond to microbes or “invaders” in general, not specific to any bacteria, virus, or fungus.

Lymphatic System – circulates fluid and white blood cells back to blood Organs of the lymphatic system include the lymph nodes and spleen, which trap “invaders”

Lymphatic System – circulates fluid and white blood cells back to blood The lymphatic system also includes the bone marrow and thymus, where lymphocytes mature

Why does the doctor feel your lymph nodes during a regular checkup? Lymph nodes swell when the body is fighting disease, as the white blood cells in lymph nodes multiply to catch disease- causing invaders (pathogens)

Specific DefensesSpecific Defenses: Involve lymphocytes (other specialized white blood cells) responding to antigens Lymphocytes include B cells and T cells –Antigens = “antibody generators,” (ex. bacteria, viruses, fungi, cancer) - anything that causes B cells to produce antibodies –Antibodies are proteins that bind antigens to help the immune system destroy them

Each B cell and T cell has membrane receptors for one specific antigen In your blood cells, a type of recombination leads to millions of unique B cells and T cells so your body can respond to millions of different antigens

Challenge and Response –A pathogen challenges the immune system and is eaten by a phagocyte –Parts of the pathogen (antigens) are presented on the surface of the cell –A helper T cell with receptors that match that antigen is activated to start the immune response

Clonal Selection –Helper T cells and B cells that match the specific antigen (invader) are cloned –Activated B cells divide and produce plasma cells and memory cells –Plasma cells produce antibodies that attach to and mark antigens –Memory cells activate the immune system quickly next time the antigen appears

Why are the defenses above called specific? Each lymphocyte (B cell or T cell) recognizes one specific antigen, so responds to one specific pathogen (bacteria, virus, fungus, etc). Each B cell and T cell has unique receptors on its membranes to recognize an antigen.

Immune Response Primary response – first exposure to an antigen –Response is days while your body goes through clonal selection –You may get sick in the “lag time” while your body multiplies B and T effector cells to combat the disease-causing antigen

Secondary response – subsequent exposures to an antigen –Response is 2-7 days; your body makes more effectors cells than in a primary response, and antibodies/cells have a higher affinity for the antigen –You won’t get sick because your body remembers how to fight effectively

How is the difference between primary and secondary response related to vaccines? We use vaccines – a dead or non-pathogenic version of a disease-causing microbe – to expose our bodies to the antigen. Our bodies go through a primary response and create memory cells. If we are exposed to the disease-causing pathogen, our bodies respond quickly (secondary response) and we don’t get sick.

Active vs. Passive Immunity Immunity due to antibodies produced by the organism itself after challenge and response to a pathogen Immunity due to antibodies acquired from another organism through the placenta, colostrum, or injection

Polyclonal vs Monoclonal Antibodies Many B cells are activated and divide in response to various antigens on the surface or one pathogen. Many types of antibodies are produced. A specific B cell is isolated in laboratory culture to divide and produce one type of antibody.

Monoclonal antibody production

–A lab animal is injected with an antigen –The activated B cells are removed from the spleen –The B cells are fused with tumor cells (=hybridomas) –These hybrids are tested for antibody production –The desired cells are cultured to produce the antibody

Monoclonal antibody uses –Pregnancy tests – antibodies to hcg (pregnancy hormone) are fused to an enzyme that changes color if antibodies bind the hormone –Cancer treatment – how do you think antibodies could be used to fight cancer cells?

Monoclonal antibody uses –Pregnancy tests – antibodies to hcg (pregnancy hormone) are fused to an enzyme that changes color if antibodies bind the hormone –Cancer treatment – antibodies could potentially target cancer cell markers and carry toxins to tumors

Self-Recognition Your immune system must recognize your own cells so it won’t attack them MHC (major histocompatibility complex) molecules are important self markers –MHC molecules bind antigens inside white blood cells and present them on the surface to activate immune responses

Self-Recognition –MHC genes affect which antigens your MHC molecules bind, so which antigens your immune system can respond to –Summarize the dirty T-shirt study and its evolutionary explanation.dirty T-shirt studyevolutionary explanation