What triggers the release of mediators from mast cells during Type I hypersensitivity?

Correct Answer: A

Rationale: The correct answer is A. Cross-linking of IgE molecules on the mast cell surface triggers the release of mediators during Type I hypersensitivity. When allergens bind to IgE antibodies on mast cells, it leads to cross-linking of IgE molecules, causing the mast cell to release histamine and other inflammatory mediators. This process initiates the allergic response. Explanation for incorrect choices: B: Activation of complement proteins does not directly trigger mast cell degranulation in Type I hypersensitivity. C: Binding of IgG to antigen is characteristic of Type II and Type III hypersensitivity reactions, not Type I. D: Phagocytosis of allergens does not directly stimulate mast cells to release mediators in Type I hypersensitivity.

Correct Answer: B

Rationale: The correct answer is B because correctly identifying the client prior to a blood transfusion helps prevent a type II hypersensitivity reaction, which occurs when the body attacks its own cells due to mismatched blood types. This action ensures that the client receives compatible blood, reducing the risk of a transfusion reaction. Administering steroids for a positive TB test (A) is unrelated to preventing a type II hypersensitivity reaction. Keeping the client free of the offending agent (C) is more relevant to preventing a type IV hypersensitivity reaction. Providing a latex-free environment for the client (D) is important for preventing a type I hypersensitivity reaction in latex-sensitive individuals, not type II reactions related to blood transfusions.

Correct Answer: C

Rationale: The correct answer is C: Afferent lymphatics. Dendritic cells migrate from tissues to lymph nodes through afferent lymphatics, which are small vessels that carry lymph into the lymph nodes. Once inside the lymph nodes, dendritic cells interact with T cells to initiate immune responses. The thoracic duct (A) drains lymph from the entire body into the bloodstream, not directly into lymph nodes. High endothelial venules (HEV) (B) are specialized blood vessels in lymph nodes where lymphocytes enter from the bloodstream, not dendritic cells. Efferent lymphatics (D) carry lymph out of the lymph nodes, not into them.

Correct Answer: B

Rationale: The correct answer is B: Signal propagation in T cells. CD3 is a protein complex found on the surface of T cells that is crucial for T cell receptor signaling and activation. It helps propagate signals within T cells, leading to T cell activation and immune responses. Choice A (Antigen binding) is incorrect as CD3 is not directly involved in antigen binding. Choice C (Signal propagation in B cells) is incorrect as CD3 is specific to T cells, not B cells. Choice D (T cell homing to lymph nodes) is incorrect as CD3 is not responsible for the physical migration of T cells to lymph nodes.

Correct Answer: E

Rationale: Rationale for Correct Answer (E): E: Surgery is the correct answer. Surgery is not typically used as a primary therapy for autoimmune diseases. Autoimmune diseases are usually treated with medications such as immuno-suppressive drugs (A), anti-inflammatory drugs (B), and targeted therapies like anti-TNF (C) and anti-CD20 (D) to manage symptoms and control the immune response. Surgery is only considered in specific cases when other treatments have failed or for complications related to the autoimmune disease. Therefore, surgery is not a standard therapy for autoimmune diseases. Summary of Incorrect Choices: A: Immuno-suppressive drugs like cortisone are commonly used in autoimmune disease treatment. B: Aspirin is an anti-inflammatory drug that can help manage symptoms in some autoimmune diseases. C: Anti-TNF therapy targets specific molecules involved in the immune response in autoimmune diseases. D: Anti-CD20 therapy targets B cells to modulate the immune response in autoimmune diseases.