Bauman Chapter 18 Answers to Critical Thinking Questions p. 516 During the Gulf War in 2003, an Army corporal with type AB blood received a life-saving blood transfusion from his sergeant who had type O blood. Later the sergeant was involved in a traumatic accident and needed blood desperately. The corporal wanted to help but was told his blood was incompatible. Explain the immunological reasons the corporal could receive from but could not give to the sergeant. The O blood type lacks two antigens (A and B) that can trigger an immune response, and is therefore safe to give to a person of any blood type (this is why people with O blood type are sometimes referred to as “universal donors”). The corporals’ blood carries both A and B antigens and will provoke an immune response in anyone who does not have both A and B antigens, since their blood contains antibodies to one or both of the antigens. p. 522 A patient arrives at the doctor’s office with a rash covering her legs. How could you determine if the rash were a type I or a type IV hypersensitivity? A patient history may provide information about the time between exposure and the first signs of rash: If only a couple of hours separate the exposure and response, it is a type I hypersensitivity, while if a day or more elapsed before the rash developed it is a type IV reaction. If the irritant is unknown, the history is not revealing. Itching at the rash site suggests a type I hypersensitivity reaction, and may be verified by applying antihistamine topically: Ifthe itching and redness subside, the rash is a type I reaction. A rash that does not itch may be a type VI hypersensitivity reaction, which will be responsive to corticosteroids instead of antihistamines. p. 527 A 42-year-old woman has been diagnosed with rheumatoid arthritis. Unable to find relief from her symptoms, she seeks treatment from a doctor in another country who injects a daily regimen of antibodies and complement into her afflicted joints. Do you expect the treatment to improve her condition? Explain your reasoning. No, the treatment likely will make her condition more severe. Rheumatoid arthritis is an autoimmune disease mediated by antibody responses and complement activation, so additional antibodies and complement is more likely to compound the damage. p. 528 Two boys have autoimmune diseases: One has Bruton-type agammaglobulinemia, and the other has DiGeorge anomaly. On a camping trip, each boy is stung by a bee and each falls into poison ivy. What hypersensitivity reactions might each boy experience as a result of his camping mishaps? Bee stings result in type I hypersensitivity reactions, mediated by IgE antibodies. The child with Bruton-type agammaglobulinemia lacks B cells capable of producing IgE and thus does not have an allergic reaction to the sting. On the other hand, the child with DiGeorge anomaly does have antibodies and develops a type I hypersensitivity reaction to the bee sting. The irritant in poison ivy triggers cell-mediated type VI hypersensitivity reactions, so the child with Bruton-type agammaglobulinemia has a contact dermatitis allergic reaction to the poison ivy. The DiGeorge anomaly child lacks T cells and so does not have a contact dermatitis reaction to the poison ivy. p. 531 1. What possible advantages might an individual gain from making class E antibodies (IgE)? Some of the primary targets of IgE are parasitic worms, therefore people exposed to internal parasites benefit from IgE antibody production. 2. Why can’t physicians use skin tests similar to the tuberculin reaction to diagnose other bacterial diseases? The tuberculin skin test takes advantage of the fact that Mycobacterium tuberculosis produces a unique antigen protein that provokes a cell-mediated hypersensitivity response. Few other bacteria have unique antigens that trigger type VI hypersensitivity reactions, the immune responses to most bacterial infections are antibody-mediated. 3. In both Graves’ disease and juvenile onset diabetes mellitus, autoantibodies are directed against cytoplasmic membrane receptors. Speculate on the clinical consequences of an autoimmune response to estrogen receptors. An autoimmune response to estrogen receptors will produce systemic consequences because a variety of cells have estrogen receptors. Fertility will be reduced due to damage to the ovaries, and the menstrual cycle will be altered because endometrial cells will be damaged. Cells with roles in bone growth have estrogen receptors, so bone growth and remodeling will be impaired. The hypothalamus also has estrogen receptors and may be targeted as well (it is not protected by the blood-brain barrier) with a huge diversity of possible consequences since the hypothalamus is central to regulating most endocrine functions. On the other hand, an immune response targeting estrogen receptors would be beneficial in fighting certain types of estrogen-responsive cancers (some types of breast and ovarian cancers). 4. In general, people with B cell defects acquire numerous bacterial infections, whereas those with T cell defects get viral diseases. Explain why this is so. Antibody-mediated responses are particularly effective in fighting infections with extracellular pathogens like bacteria; therefore, people who lack B cells suffer from bacterial infections. Cell-mediated immune responses are more effective in fighting intracellular pathogens like viruses; therefore, people who lack T cells likely will succumb to viral infections. 5. What types of illnesses cause death in patients with combined immunodeficiencies or AIDS? Persons with AIDS or combined immunodeficiencies die of opportunistic infections. 6. Because of the severe shortage of organ donors for transplants, many scientists are examining the possibility of using organs from nonhuman species such as pigs. What special clinical problems might be encountered when using these xenografts? Tissue matching is not possible for xenografts because other mammals have very different MHC genes and proteins, and the xenografts have many other antigens that are recognized as non-self. Such xenografts therefore require immunosuppressive therapy that in turn leaves the recipient highly susceptible to opportunistic infections, which may be deadly.