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| Inquiry Questions FIGURE 48.11 IgM and IgG antibodies. The first antibodies produced in the humoral immune response are IgM antibodies, which are very effective at activating the complement system. This initial wave of antibody production peaks after about one week and is followed by a far more extended production of IgG antibodies. Why does the production of IgM antibodies cease after one week? Answer: IgM is the body's defensive response to a primary infection and if this defense is going to be effective, it will be so within a week. There is no point in continuing production, because within a week after an infection begins, the secondary response of IgG plasma cells kick in. FIGURE 48.15 The development of active immunity. Immunity to smallpox in Jenner's patients occurred because their inoculation with cowpox stimulated the development of lymphocyte clones with receptors that could bind not only to cowpox but also smallpox antigens. A second exposure stimulates the immune system to produce large amounts of the antibody more rapidly than before. Would a secondary exposure to cowpox rather than smallpox have produced as strong an antibody response? Answer: Yes, the secondary response would be just as strong. The lymphocytes that were cloned following the first exposure have receptors that bind to the cowpox virus. It just so happens that the antigens on the smallpox virus are so similar to the antigens on the cowpox virus that they are recognized by these same lymphocytes. FIGURE 48.24 Survival of T cells in culture after exposure to HIV. The virus has little effect on the number of CD8+ cells, but it causes the number of CD4+ T cells to decline dramatically. Are the surviving CD4+ T cells any different than those destroyed? How could you be sure? Answer: If surviving CD4+ T cells are somehow more resistant to HIV, then the cell culture prepared from these survivors should not show dramatic declines in cell numbers after HIV infection. Self Test 1). The epidermis fights microbial infections by a). making the surface of the skin acidic. b). excreting lysozyme to attack bacteria. c). producing mucus to trap microorganisms. d). all of these. Answer: d 2). Cells that target and kill body cells infected by viruses is are a). macrophages. b). natural killer cells. c). monocytes. d). neutrophils. Answer: b 3). A molecule present on the plasma membrane that induces an immune response is called a). an antigen. b). an interleukin. c). an antibody. d). a lymphocyte. Answer: a 4). Which one of the following acts as the "alarm signal" to activate the body's immune system by stimulating helper T cells? a). B cells b). interleukin-1 c). interleukin-2 d). histamines Answer: b 5). Cytotoxic T cells are called into action by the a). presence of histamine. b). presence of interleukin-1. c). presence of interleukin-2. d). B cell stimulating factor. Answer: c 6). The immunoglobin ________ is involved in the primary response to an invading microorganism, and ________ is involved in the secondary response. a). IgG / IgM b). IgM / IgE c). IgE / histamines d). IgM / IgG Answer: d 7). How does your body detect millions of different antigens? a). The few hundred immunoglobulin genes can be rearranged or can undergo mutations to form millions of antibody molecules. b). There are millions of different antibody genes. c). The few hundred immunoglobulin genes undergo antigen shifting. d). Each B cell has a different set of immunoglobulin genes, and so the activation of different B cells produces different antibodies. Answer: a 8). The blood from a person with an AB blood type a). would agglutinate with anti-A antibodies only. b). would agglutinate with anti-B antibodies only. c). would agglutinate with both anti-A and anti-B antibodies. d). would not agglutinate with either anti-A or anti-B antibodies. Answer: c 9). The HIV virus is particularly dangerous because it attacks a). cells with the CD4+ coreceptor. b). helper T cells. c). 60 to 80% of circulating T cells in the body. d). all of these. Answer: d 10). Diseases in which the person's immune system no longer recognizes its own MHC proteins are called a). allergies. b). autoimmune diseases. c). immediate hypersensitivity. d). delayed hypersensitivity. Answer: b Test Your Visual Understanding 1). When a children have chicken pox, they run a fever and develop a rash that leaves them contagious for 5 to 7 days. In that time, the immune system mounts an attack resulting in the production of antibodies that help the cells of the immune system fight the infection. If these children are exposed to the chicken pox virus again, they do not develop the disease. Using the figure above, explain why a person doesn't develop chicken pox a second time. Answer: When the child is first exposed to the chicken pox virus, the immune system is "starting from scratch" to mount its attack. Macrophages, neutrophils, and natural killer cells begin the attack. Macrophages then stimulate the proliferation of helper T cells. Helper T cells, through the release of interleukin-2, activate B cells. The B lymphocytes, shown in the figure, transform into plasma cells that begin producing the specific antibodies that will help the immune system fight off the chicken pox infection. This whole process can take several days, which is why the child exhibits the symptoms and is contagious for 5 to 7 days. However, at the same time the B cells are transforming into plasma cells, they are also transforming into memory cells, which produces a clone of memory cells. This battery of memory cells is all prepared to begin producing the antibodies specific to the chicken pox virus. Later in life, if the chicken pox virus enters the body, the memory cells quickly transform into plasma cells and begin producing antibodies. This occurs in a matter of hours, not days as with the first infection. Therefore, the new virus doesn't have a chance to establish an infection the second time around. Apply Your Knowledge 1). Sometimes a doctor may order a differential blood count to determine whether a person has an infection. The differential blood count detects the levels of white blood cells (WBCs) in the body. Elevated white blood counts indicate an infection. The normal ranges of WBCs in the body are approximately: neutrophils—60% lymphocytes—25% monocytes—8% eosinophils—4% basophils—3% A man has a total WBC of 6000/ml, and the differential blood count values are: neutrophils, 3720/ml; lymphocytes, 1500/ml; monocytes, 480/ml; eosinophils, 180/ml; basophils, 120/ml. Is his WBC within normal range? Answer: In order for the patient to have a normal WCB count, the values of his differential count should be close to the indicated percentages. The total WBC count is 6000/ml, therefore: The % of neutrophils is 3720/6000 = 0.62 or 62% The % of lymphocytes is 1500/6000 = 0.25 or 25% The % of monocytes is 480/6000 = 0.08 or 8% The % of eosinophils is 180/6000 = 0.03 or 3% The % of basophils is 120/6000 = 0.02 or 2% The patient's differential blood count is essentially normal. He has no clear infection. |