Which condition is caused by a Type IV hypersensitivity reaction?

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: 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.

Correct Answer: B

Rationale: The correct answer is B: IL-2. IL-2 is essential for the clonal expansion of T cells as it promotes T cell proliferation. It is produced by activated T cells themselves and plays a crucial role in regulating immune responses. IL-1 is involved in inflammation, not T cell expansion. IL-4 is important for Th2 cell differentiation, while IL-5 is critical for eosinophil activation. In summary, IL-2 specifically promotes T cell clonal expansion, making it the correct choice in this context.

Correct Answer: D

Rationale: The correct answer is D because T regulatory cells are known to suppress immune responses and promote immune tolerance, which is opposite to causing immunity. Choice A is incorrect because T regulatory cells are indeed generated in the thymus upon expression of Foxp3. Choice B is incorrect as T regulatory cells can also be generated in the periphery in response to cytokines. Choice C is incorrect as T regulatory cells are known to inhibit effector T cells to regulate immune responses.

Correct Answer: B

Rationale: The correct answer is B: Hepatitis B. Recombinant vaccines are made by inserting genetic material from a pathogen into another organism to stimulate an immune response. Hepatitis B vaccine is produced using recombinant DNA technology to create a non-infectious protein that triggers an immune response against the hepatitis B virus. DPT, BCG, and Measles vaccines are not examples of recombinant vaccines as they are made using different methods without genetic engineering.