A multilineage cytokine among the ILs is:

Correct Answer: C

Rationale: The correct answer is C: IL-3. IL-3 is a multilineage cytokine that stimulates the growth and differentiation of multiple blood cell lineages. It acts on various stem cells to promote the production of different types of blood cells. IL-1 is mainly involved in inflammation and immune response, not multilineage effects. IL-2 primarily regulates T cell growth and function. IL-4 promotes B cell growth and IgE production. Therefore, IL-3 is the correct answer as it is specifically known for its multilineage effects on blood cell development.

Correct Answer: B

Rationale: The correct answer is B: Monoclonal protein in serum or urine. Multiple myeloma is characterized by the presence of abnormal plasma cells in the bone marrow, which produce monoclonal proteins. These proteins can be detected in the blood or urine through electrophoresis. Fever and infection (Choice A) are common symptoms but not specific to multiple myeloma. Elevated platelet count (Choice C) is not a characteristic feature of multiple myeloma. Normal bone marrow (Choice D) is not consistent with the disease, as multiple myeloma involves abnormal plasma cell proliferation in the bone marrow.

Correct Answer: B

Rationale: The correct answer is B because the principal difference between cytotoxic (type II) and immune complex (type III) hypersensitivity lies in the site where antigen-antibody complexes are formed. In type II hypersensitivity, the complexes form on the surface of target cells, leading to cell destruction. In contrast, in type III hypersensitivity, the complexes form in circulation or in tissues, leading to immune complex deposition and subsequent tissue damage. The other choices are incorrect because the class of antibody (A), participation of complement (C), and participation of T cells (D) can be common features in both type II and type III hypersensitivity reactions, but the crucial distinguishing factor is where the complexes are formed.

Correct Answer: C

Rationale: The correct answer is C because AIDS is caused by the human immunodeficiency virus (HIV), which specifically targets and kills CD4-positive T lymphocytes. These cells are crucial for coordinating the immune response. A, B, and D are incorrect because HIV primarily affects CD4-positive T cells, not B lymphocytes, lymphocyte stem cells, or CD8-positive T cells. This leads to a weakened immune system, making individuals more susceptible to infections and other complications associated with AIDS.

Correct Answer: D

Rationale: The correct answer is D: decreased resistance to Neisseria bacteremia. This is because C6 is a component of the complement system, which plays a crucial role in the immune response against Neisseria bacteria. A deficiency in C6 would impair the ability to effectively combat Neisseria infections. Choice A is incorrect because the deficiency of C6 does not directly affect resistance to viral infections. Choice B is incorrect as hypersensitivity reactions are not specifically linked to C6 deficiency. Choice C is incorrect because there is no direct correlation between C6 deficiency and an increased frequency of cancer.