Which hypersensitivity type is mediated by T cells?

Correct Answer: D

Rationale: The correct answer is D: Type IV hypersensitivity. This type is mediated by T cells, specifically CD4+ helper T cells and CD8+ cytotoxic T cells. The process involves antigen-presenting cells activating T cells, leading to a delayed response. Choices A, B, and C involve different mechanisms and are not mediated by T cells. Type I is mediated by IgE antibodies, Type II involves antibody-mediated cell destruction, and Type III involves immune complex deposition. Therefore, Type IV is the only hypersensitivity type directly mediated by T cells.

Correct Answer: A

Rationale: The correct answer is A because histamine released from mast cells causes increased vascular permeability, leading to edema, and bronchoconstriction, contributing to respiratory symptoms. This is a key mechanism in allergic reactions. B: Neutralization of antigens and opsonization are functions of antibodies, not histamine. C: Complement activation and T cell proliferation are separate immune responses not mediated by histamine. D: Direct lysis of pathogens is typically carried out by immune cells like macrophages and natural killer cells, not histamine.

Correct Answer: B

Rationale: The correct answer is B: Sarcoidosis. Type IV hypersensitivity reactions are mediated by T cells and are characterized by delayed onset inflammatory responses. Sarcoidosis is a granulomatous disease where T cells form granulomas in affected tissues. Anaphylaxis (A) is a Type I hypersensitivity reaction involving IgE antibodies. Grave's disease (C) is an autoimmune disorder caused by Type II hypersensitivity reaction mediated by antibodies. Goodpasture's syndrome (D) is a Type II hypersensitivity reaction involving antibodies attacking basement membranes. Therefore, the correct answer is B as it fits the characteristics of a Type IV hypersensitivity reaction.

Correct Answer: B

Rationale: The correct answer is B. Baby powder is not recommended for individuals with systemic lupus erythematosus, as it can irritate the skin and worsen symptoms. A: Avoiding direct sunlight is crucial due to photosensitivity. C: Grouping errands helps conserve energy. D: Rest is important to manage fatigue. Summary: A, C, and D are all appropriate self-care measures for a client with systemic lupus erythematosus, while using baby powder is not recommended.

Correct Answer: A

Rationale: The correct answer is A: Germinal center. Germinal centers are specialized regions within lymph nodes where B cells undergo intense proliferation, somatic hypermutation, and class switching to generate high-affinity antibodies. This process is crucial for the adaptive immune response. Paracortex (B) contains T cells, not B cells. Medulla (C) is mainly involved in filtering lymph. Infected tissue (D) is not a specific site for B cell proliferation.