Nokea
Which of the following leukocytes is involved in antibody-dependent cell-mediated cytotoxicity?
- A. Natural Killer (NK) cells
- B. Neutrophils
- C. Macrophages
- D. Mast cells
Correct Answer: A
Rationale: The correct answer is A: Natural Killer (NK) cells. NK cells are involved in antibody-dependent cell-mediated cytotoxicity by recognizing target cells coated with antibodies and inducing their death. NK cells play a crucial role in immune surveillance and defense against infected or malignant cells. Neutrophils, macrophages, and mast cells are not directly involved in antibody-dependent cell-mediated cytotoxicity. Neutrophils are primarily responsible for phagocytosis, macrophages are antigen-presenting cells, and mast cells are involved in allergic reactions.
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L-Selectin is
- A. Expressed on effector T cells
- B. Expressed on HEV
- C. Expressed on naïve T cells
- D. Required to extravasate into tissues
Correct Answer: C
Rationale: The correct answer is C: Expressed on naïve T cells. L-Selectin is a cell adhesion molecule expressed on the surface of naïve T cells. It plays a crucial role in the initial attachment of T cells to high endothelial venules (HEV) in lymphoid tissues, facilitating T cell entry into lymph nodes. It specifically binds to ligands on HEV, allowing T cells to extravasate into lymphoid tissues. Choice A is incorrect because L-Selectin is primarily expressed on naïve T cells rather than effector T cells. Choice B is incorrect as L-Selectin is expressed on HEV, not by them. Choice D is incorrect because L-Selectin is involved in the initial attachment of T cells to endothelial cells, rather than being required for extravasation into tissues.
Which rationale describes treatment of atopic allergies with immunotherapy?
- A. It decreases the levels of allergen-specific T helper cells.
- B. It decreases the level of IgE so that it does not react as readily with an allergen.
- C. It stimulates increased IgG to bind with allergen-reactive sites, preventing mast cell-bound IgE reactions.
- D. It gradually increases the amount of allergen in the body until it is no longer recognized as foreign and does not elicit an antibody reaction.
Correct Answer: C
Rationale: Immunotherapy stimulates the production of blocking IgG antibodies, which compete with IgE for allergen-binding sites, preventing mast cell activation.
Which group(s) of microorganisms is (are) thought to be the oldest living organisms?
- A. eukaryotes
- B. heterotrophic prokaryotes
- C. Archaea
- D. viruses
Correct Answer: C
Rationale: The correct answer is C: Archaea. Archaea are thought to be the oldest living organisms due to their unique characteristics and genetic similarities to the earliest forms of life. They are known for thriving in extreme environments, resembling conditions on early Earth. Other choices are incorrect because eukaryotes are more complex and evolved later, heterotrophic prokaryotes came after autotrophic prokaryotes, and viruses are not considered living organisms.
What is the significance of isotype switching in B cells?
- A. It enables the production of IgM only
- B. It enhances antibody affinity for antigens
- C. It changes the constant region to produce different antibody isotypes
- D. It eliminates antigen-specific B cells
Correct Answer: C
Rationale: Isotype switching in B cells involves changing the constant region to produce different antibody isotypes, such as IgG, IgA, or IgE. This is important for diversifying the functions of antibodies without altering antigen specificity. It allows for different effector functions, such as opsonization, neutralization, or complement activation. This process does not eliminate antigen-specific B cells, as it maintains the immunological memory. Isotype switching does not directly affect antibody affinity for antigens, which is primarily determined by somatic hypermutation and affinity maturation. It is not limited to producing IgM only, as B cells can switch to other isotypes based on the cytokine microenvironment.
What is the medical term for an abnormal decrease in platelets?
- A. Leukopenia
- B. Thrombocytopenia
- C. Anemia
- D. Hemolysis
Correct Answer: B
Rationale: The correct answer is B: Thrombocytopenia, which refers to an abnormal decrease in platelets. Platelets are crucial for blood clotting. Leukopenia (A) is a decrease in white blood cells, not platelets. Anemia (C) is a decrease in red blood cells, not platelets. Hemolysis (D) is the breakdown of red blood cells, not related to platelet count. Therefore, B is the correct answer as it specifically addresses a decrease in platelet count, leading to potential bleeding issues.