Polyomavirus causes tumors in 'nude mice' but not in normal mice, the BEST interpretation is that

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 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.

Correct Answer: D

Rationale: The correct sequence for setting up a complement fixation test for antibodies is as follows: Ag + patient's serum + C (complement) / wait / + EA (erythrocyte antigen). This sequence ensures that the patient's serum containing antibodies is mixed with the antigen (Ag) first to allow for antibody-antigen binding. Then, complement (C) is added to the mix to activate the complement fixation process. Finally, erythrocyte antigen (EA) is added to observe any hemolysis indicating the presence of antibodies. This order is crucial for accurate test results. Incorrect choices: A: Incorrect sequence, as patient's serum should be mixed with Ag first. B: Incorrect sequence, as C should be added before EA. C: Incorrect sequence, as EA should be added last for hemolysis observation.

Correct Answer: A

Rationale: The high ratio of IgM to IgG antibodies indicates an acute infection, as IgM is produced initially and declines over time while IgG increases for long-term immunity. Choice A is correct because a high IgM to IgG ratio suggests a recent encounter with the virus, making it unlikely the patient has been previously exposed. Choices B, C, and D are incorrect because they do not address the specific antibody response pattern seen in acute viral infections.