What is the most likely diagnosis for this man? (50-year-old with breathlessness, bone pain, severe infections, hepatosplenomegaly, gum hypertrophy)

Correct Answer: B

Rationale: The most likely diagnosis for this man is Acute Myeloid Leukemia (AML) based on his symptoms of breathlessness, bone pain, severe infections, hepatosplenomegaly, and gum hypertrophy. AML is characterized by rapid growth of abnormal white blood cells in the bone marrow, leading to bone pain, infections, and organomegaly. The presence of gum hypertrophy is a classic finding in AML due to infiltration of leukemic cells. In contrast, Multiple Myeloma (choice A) presents with bone pain, anemia, and kidney issues; Chronic Lymphocytic Leukemia (choice C) typically manifests with lymphadenopathy and anemia; and Hodgkin Lymphoma (choice D) presents with painless lymphadenopathy, fever, night sweats, and weight loss. Therefore, AML is the most fitting diagnosis in this case.

Correct Answer: C

Rationale: The correct answer is C because T lymphocytes play a crucial role in the rejection of polyomavirus-induced tumors. This is evident from the fact that nude mice, which lack functional T lymphocytes, develop tumors when infected with polyomavirus, whereas normal mice with intact T lymphocytes do not. Choice A is incorrect because macrophages are not the main players in rejecting these tumors. Choice B is incorrect as natural killer cells alone cannot reject these tumors without the help of T lymphocytes. Choice D is incorrect as B lymphocytes may also contribute to the rejection process, although they are not the primary effector cells in this context.

Correct Answer: B

Rationale: The correct answer is B because a positive tuberculin skin test indicates a cell-mediated immune response. This is because the test measures the response of T cells to the antigen, which is indicative of an active cellular immune response against Mycobacterium tuberculosis. Option A is incorrect as it refers to a humoral immune response involving antibodies produced by B cells. Option C is incorrect because the test specifically assesses T cell function, not both T and B cells. Option D is incorrect as it implies that only B cells are responsible for the positive skin test, which is not the case.

Correct Answer: B

Rationale: The correct sequence for testing a patient for antibody against the AIDS virus with the ELISA procedure is B. Step 1: HIV antigen is immobilized on a solid surface. Step 2: Patient's serum containing antibodies is added. Step 3: Enzyme-labeled antibody against human gamma globulin is added to detect patient antibodies. Step 4: Enzyme substrate is added to produce a measurable signal. This sequence allows for the detection of patient antibodies against the HIV antigen. Choices A, C, and D are incorrect because they do not follow the correct order of steps for an ELISA test. In these options, the order of the components is not suitable for detecting antibodies in the patient's serum effectively.

Correct Answer: B

Rationale: The correct answer is B because idiotypic determinants are unique to each antibody, so an antibody directed against the idiotypic determinants of a human IgG antibody would react with another antibody produced by the same plasma cell that produced the IgG, which would be an IgM antibody. Choice A is incorrect because idiotypic determinants are not located in the Fc region. Choices C and D are incorrect because idiotypic determinants are specific to the variable regions of antibodies, not the constant regions or the kappa/gamma chains.