What is the structural composition of an antibody?

Correct Answer: A

Rationale: The correct answer is A: Two heavy chains and two light chains. Antibodies are composed of two identical heavy chains and two identical light chains. Heavy chains provide structural support and effector functions, while light chains contribute to antigen binding. Choice B is incorrect as antibodies do not have three heavy chains. Choice C is incorrect as antibodies do not have three light chains. Choice D is incorrect as antibodies do not have four heavy chains.

Correct Answer: B

Rationale: The correct answer is B because Type V hypersensitivity involves antibodies stimulating receptors instead of destroying them. In Type II hypersensitivity, antibodies target antigens on cell surfaces, leading to cell destruction. In Type V, antibodies bind to cell receptors, causing abnormal receptor activation. Choices A, C, and D are incorrect because Type V hypersensitivity is not mediated by T cells (A), does not involve immune complex formation (C), and does involve the immune system (D). Therefore, the unique characteristic of Type V hypersensitivity is the stimulation of receptors by antibodies, making choice B the correct answer.

Correct Answer: B

Rationale: The correct answer is B: Systemic release of vasoactive mediators. Anaphylaxis is a severe allergic reaction that is primarily caused by the systemic release of vasoactive mediators such as histamine, prostaglandins, and leukotrienes from mast cells and basophils. These mediators lead to widespread vasodilation, increased vascular permeability, bronchoconstriction, and systemic hypotension, resulting in the characteristic symptoms of anaphylaxis. Choice A (Immune complex deposition) is incorrect because anaphylaxis is not caused by the deposition of immune complexes but rather by the immediate hypersensitivity reaction. Choice C (Localized mast cell degranulation) is incorrect because anaphylaxis involves systemic mast cell degranulation leading to widespread effects throughout the body, not just localized reactions. Choice D (T cell activation) is incorrect because anaphylaxis is primarily mediated by IgE antibodies and mast cells, not T cells.

Correct Answer: B

Rationale: The correct answer is B: Glomerular basement membrane. In SLE, immune complexes deposit in various tissues, leading to inflammation and damage. The glomerular basement membrane is a common site for immune complex deposition in SLE, resulting in lupus nephritis. The other choices are incorrect because immune complex deposition does not typically occur in the thyroid, peripheral nerves, or mast cells in SLE. Thyroid involvement in SLE is more related to autoimmune thyroiditis, while peripheral nerves are not a major site for immune complex deposition in this condition. Mast cells are primarily involved in allergic reactions and are not a major target in SLE.

Correct Answer: B

Rationale: The correct answer is B: Epinephrine. Epinephrine is the first-line treatment for anaphylaxis as it rapidly reverses the symptoms by constricting blood vessels, relaxing airway muscles, and increasing heart rate. It is crucial in preventing severe complications and can be life-saving. Antihistamines (choice A) only target histamine effects, which are not sufficient in managing anaphylaxis. Corticosteroids (choice C) are used as adjunct therapy but are not as immediate or critical as epinephrine. Antibiotics (choice D) are not indicated for anaphylaxis treatment. Therefore, epinephrine is the most appropriate choice for managing anaphylaxis effectively.