A patient with rheumatic fever develops a sore throat... 7 days after initiation of penicillin therapy the patient develops a fever of 103°F, a generalized rash, and proteinuria. This MOST probably resulted from

Correct Answer: D

Rationale: The correct answer is D: an IgG-IgM response to penicillin. 1. The symptoms of fever, rash, and proteinuria are suggestive of a hypersensitivity reaction to penicillin. 2. The timing of 7 days after penicillin initiation is consistent with a delayed hypersensitivity reaction mediated by IgG and IgM antibodies. 3. Recurrence of rheumatic fever typically occurs weeks to months after the initial episode, making choice A incorrect. 4. Choice B is unlikely given the temporal relationship with penicillin therapy. 5. Choice C is incorrect as an IgE response would present as an immediate hypersensitivity reaction, not after 7 days.

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.

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.