Transcript Document
I. Nonspecific defences A. Species resistance B. Mechanical barriers (skin, mucous membranes, sweat, sloughing epidermis) form the first line of defense. C. Chemical barriers (along with D-G) form the second line of defense. 1. Enzymes 2. Interferons are made by some virus infected cells. They will bind to receptors on uninfected cells to block the entrance of a variety of other viruses. 3. Defensins are made when non-self cells are recognized. Some of them work by poking holes in bacterial cell walls and membranes. 4. Collectins recognize a variety of bacteria, yeast, and some viruses. They grab onto them and hook them up together so that they can be easily phagocytized. D. Fever - Infection causes lymphocytes to make interleukin-1 that causes the body’s temperature set point to increase. This causes the liver and spleen to hold onto iron, reducing its levels in the blood. Without iron, bacteria and viruses reproduce more slowly. E. NATURAL KILLER CELLS (lymphocytes) provide protection against some viruses and cancer by secreting PERFORINS that disintegrate the cell membranes of infected cells. They also speed up inflammation. F. INFLAMMATION - localized redness, swelling, heat and pain results from leaky blood vessels enabling white blood cells to reach the site of infection. G. Phagocytes engulf and destroy pathogens. II. ANTIGENS are molecules (proteins, sugars, glycoproteins, or glycolipids) that extend from the surface of a foreign cell to signal the body that it doesn’t belong. III. Specific defenses (adaptive) immunity A. Lympocyte origins 1. During fetal development undifferentiated lymphocytes are released into circulation by red bone marrow. 2. Lymphocytes that reach the thymus differentiate into T-cells/T-lymphocytes. 3. B lymphocytes/B-cells differentiate in the red bone marrow. B. Lymphocyte functions 1. Cellular immune response/cell mediated immunity a. T cells become activated by the presence of ANTIGEN-PRESENTING CELLS (Macrophages and B-cells that have processed antigens on their surface). b. HELPER T CELLS become activated when their antigen receptors combine with foreign antigens. Helper T cells stimulate B cells to make antibodies for the antigens they present. c. CYTOTOXIC T CELLS recognize nonself antigens from cancerous or virus infected cells. When they bind to antigens, they begin to make clones. Cytotoxic T cells release PERFORIN that cuts holes in cells to destroy them. d. MEMORY T CELLS are made upon initial exposure to an antigen. They provide a no-delay response for future exposure. 2. Humoral immune response a. Some B cells can become activated from binding with antigens that fit in their antigen receptors. Most B cells need helper T cells to activate. b. When activated helper T cells encounter a B cell-antigen complex, they release cytokine proteins that stimulate the B cell to proliferate. 1. Cytokines can also be released to inhibit B cell function. c. Some activated B cells can differentiate into MEMORY cells that can rapidly respond to subsequent exposure to antigens. d. PLASMA cells are differentiated B cells that produce antibodies similar to antigen receptor molecules on the original B cells surface. A single plasma B cell can only produce one kind of antibody. IV. Antibody actions A. Direct attack - antibodies cause antigens to clump so they can easily be phagocytized. B. COMPLEMENT - when certain antibodies bind, the release compliment protein that acts in a variety of ways: making antigens more susceptible to phagocytosis, attracting macrophages and neutrophils, clumping, rupturing membranes of foreign cells, altering the molecular structure of viruses to make them harmless. C. Prevent the spread of antigens V. Immune responses A. A primary immune response will usually produce detectable levels of antibodies in the blood within 5 to 10 days following infection. B. Because of memory B cells, a secondary immune response will usually produce detectable levels of antibodies in the blood within 1 day. VI. Classifications of immunity (worksheet) V. Allergies result form an immune attack on non-harmful substances. VI. Autoimmunity results when the immune system fails to distinguish self from non-self and the body attacks itself.