MCAT Biology Review
Chapter 8: The Immune System
1. In DiGeorge syndrome, the thymus can be completely absent. The absence of the thymus would leave an individual unable to mount specific defenses against which of the following types of pathogens?
2. Which of the following are NOT involved in cell-mediated immunity?
1. Memory cells
2. Plasma cells
3. Cytotoxic cells
4. Suppressor cells
3. The lymphatic system:
1. transports hormones throughout the body.
2. transports chylomicrons to the circulatory system.
3. causes extravasation of fluid into tissues.
4. is the site of mast cell activation.
4. Which of the following are involved in antibody production?
1. Plasma cells
2. Memory cells
3. Helper T-cells
4. Cytotoxic cells
5. Which of the following is NOT an example of a nonspecific defense mechanism?
1. Skin provides a physical barrier against invasion.
2. Macrophages engulf and destroy foreign particles.
3. An inflammatory response is initiated in response to physical damage.
4. Cytotoxic T-cells destroy cells displaying foreign antigens.
6. Which of the following is an example of adaptive immunity?
1. PRRs recognize that a pathogen is an invasive parasite and eosinophils are recruited to the area.
2. Complement is activated, causing osmotic instability in a bacterium.
3. B-cells generated through vaccination are activated when their antigen is encountered.
4. Dendritic cells sample bacteria within a laceration and travel to the lymph nodes to present the antigen.
7. Which of the following is true regarding passive and active immunity?
1. Active immunity requires weeks to build, whereas passive immunity is acquired immediately.
2. Active immunity is short-lived, whereas passive immunity is long-lived.
3. Active immunity may be acquired during pregnancy through the placenta.
4. Passive immunity may be acquired through vaccination.
8. Where are most self-reactive T-cells eliminated?
2. Lymph nodes
3. Bone marrow
9. What is the response of the immune system to downregulation of MHC molecules on somatic cells?
1. B-cells are activated and antibodies are released.
2. T-cells are activated, resulting in a cytotoxic response.
3. Natural killer cells induce apoptosis of affected cells.
4. Macrophages engulf the pathogen and display its antigens.
10.Which of the following correctly indicates the response of CD8+ T-cells when activated?
1. Secretion of cytotoxic chemicals
2. Causing isotype switching
3. Presentation of antigens
4. Activation of B-cells
11.Lymphoma is cancer of the cells of the lymphoid lineage. These cells often reside within lymph nodes. What type of cell is NOT likely to cause a lymphoma?
1. CD8+ T-cells
4. Th1 cells
12.Upon encountering an antigen, only T-cells with the specific T-cell receptor are activated. This is an example of:
1. innate immunity.
2. a cytotoxic T-cell response.
3. humoral immunity.
4. clonal selection.
13.Which cell type is a phagocyte that attacks bacterial pathogens in the bloodstream?
4. Dendritic cells
14.What type of immunity is likely to be affected by removal of the spleen?
1. Cytotoxic immunity
2. Humoral immunity
3. Innate immunity
4. Passive immunity
15.Which of the following cell types is NOT a granulocyte?
2. Mast cell
Answers and Explanations
1. AT-lymphocytes, which mature in the thymus, are the only specific defense against intracellular pathogens. While some bacteria, fungi, and parasites can live intracellularly, viruses—by definition—must replicate within cells. The absence of T-cells would leave an individual unable to fight viral infections with specific defenses.
2. BThe lymphocytes involved in cell-mediated immunity are the T-lymphocytes, or T-cells. There are four types of T-cells, each playing a different role in cell-mediated immunity: cytotoxic T-cells, helper T-cells, memory T-cells, and suppressor T-cells. Thus, from the answer choices, the only cells not involved in cell-mediated immunity are the plasma cells, which are differentiated immunoglobulin-secreting B-lymphocytes involved in humoral immunity. Choice (B) is therefore the correct answer.
3. BThe main function of the lymphatic system is to collect excess interstitial fluid and return it to the circulatory system, maintaining the balance of body fluids. However, this is not one of the answer choices. In addition, the lymphatic system accepts chylomicrons from the small intestine and delivers them to the cardiovascular circulation. Transport of hormones is a function of the cardiovascular system, eliminating choice (A). The lymphatic system absorbs fluid that has been pushed into tissues, but does not cause the extravasation of the fluid, eliminatingchoice (C). Mast cells reside in (and are activated in) the skin and mucous membranes, eliminating choice (D).
4. AAntibodies are produced by plasma cells derived from B-lymphocytes. The other cells are all types of T-lymphocytes, although memory B-cells can also exist. Still, memory B-cells do not produce antibodies; plasma cells do.
5. DThe body employs a number of nonspecific defense mechanisms against foreign invasion. The skin and mucous membranes provide a physical barrier against bacterial invasion. In addition, sweat contains enzymes that attack bacterial cell walls. Certain passages, such as the respiratory tract, are lined with ciliated mucus-coated epithelia, which filter and trap foreign particles. Macrophages engulf and destroy foreign particles. The inflammatory response is initiated in response to physical damage. The only choice that is not a nonspecific defense mechanism is choice (D), the correct answer. Cytotoxic T-cells are involved in (specific) cell-mediated immunity.
6. CAdaptive immunity involves the activation of B-cells and T-cells specific to the encountered antigen. Any choice that conforms to this paradigm will be correct. Choice (C) indicates that B-cells are activated. Pattern recognition receptors, or PRRs, in choice (A) recognize patterns common to certain pathogens, but do not identify the specific pathogen. Complement is an example of a blood-borne nonspecific defense against bacteria, eliminating choice (B). Dendritic cells traveling to the lymph nodes in choice (D) are a part of the interaction between the innate and adaptive immune systems, but the dendritic cells themselves are nonspecific.
7. AActive immunity refers to the production of antibodies during an immune response. Active immunity may be conferred by vaccination, such as when an individual is injected with a weakened, inactive, or related form of a particular antigen that stimulates the immune system to produce antibodies. Active immunity may require weeks to build. Passive immunity, on the other hand, involves the transfer of antibodies either passively or by injection. An example would be during pregnancy, when some maternal antibodies cross the placenta and enter fetal circulation, conferring passive immunity to the fetus. Although passive immunity is acquired immediately, it is very short-lived, lasting only as long as the antibodies circulate in blood.
8. DT-cells mature in the thymus, where they are “educated.” This education involves the elimination of T-cells with improper binding to MHC–antigen complexes (positive selection) and self-reactive T-cells (negative selection). Thus, self-reactive T-cells are eliminated in the thymus.
9. CHealthy cells exhibit MHC class I molecules. Natural killer cells monitor the expression of MHC molecules on the surface of cells. Viral infection and cancer often cause a reduction in the expression of MHC class I molecules on the cell surface. Natural killer cells detect this lack of MHC and induce apoptosis in the affected cells.
10.ACD8+ T-cells are largely responsible for the cytotoxic immune response. By releasing toxic chemicals into virally infected cells, CD8+ T-cells are able to kill these cells in an effort to contain viral infections. Isotype switching refers to changes in the isotype of antibody produced, which is not caused by CD8+ cells, eliminating choice (B). Antigens are presented by macrophages, dendritic cells, certain epithelial cells, and some B-cells, eliminating choice (C). B-cells are not activated by cytotoxic T-lymphocytes, eliminating choice (D).
11.CLymphocytes arise from the lymphoid lineage, which includes B-cells and T-cells. Thus, all types of B- and T-cells are capable of causing lymphoma. Macrophages, however, are not lymphocytes and are not likely to cause lymphoma.
12.DWhen the adaptive immune system encounters an antigen, only the cells with receptors (antibodies or T-cell receptors) specific to that antigen are activated. This is known as clonal selection. While a T-cell response may be a cytotoxic response, it could also be the activation of helper T-cells; plus, this does not explain the specificity of the response, eliminating choice (B).
13.AThe only phagocytes that attack bacteria on this list are neutrophils and dendritic cells. Dendritic cells are able to sample and present any type of material, and reside in the skin. Neutrophils, on the other hand, are present in the bloodstream and can attack bacteria present there or in tissues. Eosinophils and basophils are involved in the formation of allergies; eosinophils also defend against parasites.
14.BThe spleen is a location where B-cells mature and proliferate. Therefore, removal of the spleen is likely to result in a reduction of humoral immunity. In fact, many people receive vaccinations prior to the removal of the spleen in order to bolster their immunity.
15.AGranulocytes are cells with granules in their cytoplasm. These granules are released in immune responses to attack a pathogen. Granulocytes include neutrophils, basophils, eosinophils, and mast cells. B-cells are agranulocytes, which include lymphocytes and monocytes/macrophages.