When the clinic nurse starts to take the "air cast" off the grade 2 sprain, the patient asks why it is being removed since he still has pain. Which explanation is best?

Correct Answer: C

Rationale: The correct answer is C because long-term immobilization can indeed cause permanent disability in the case of a grade 2 sprain. Prolonged immobilization can lead to muscle atrophy, joint stiffness, and decreased range of motion, which can result in long-term disability. Choice A is incorrect because adequate circulation is more related to prolonged immobilization, not short-term removal for evaluation. Choice B is incorrect as edema is a short-term concern and not a direct result of long-term immobilization. Choice D is incorrect as there is no indication that a heavier cast will be used.

Correct Answer: C

Rationale: Step-by-step rationale: 1. "Signal 1" activation requires TCR to interact with its specific antigen. 2. TCR consists of α and β chains, which are essential for antigen recognition. 3. MHC molecule is crucial for presenting antigens to TCR for recognition. 4. Choice C (28) is not a component involved in TCR-antigen interaction. 5. Therefore, the correct answer is C as it does not contribute to "signal 1" activation. Summary: A and B are incorrect as TCR α and β chains are necessary for antigen recognition. D is incorrect as MHC molecule is essential for presenting antigens to TCR. C is correct as it is not involved in the TCR-antigen interaction process.

Correct Answer: B

Rationale: The correct answer is B because migrating dendritic cells do not enter the draining lymph node (LN) via high endothelial venules (HEV); instead, they enter through afferent lymphatic vessels. HEVs are specialized post-capillary venules in LN where lymphocytes enter from the bloodstream. Dendritic cells, carrying antigens from tissues, travel via afferent lymphatic vessels to reach the LN where they present antigens to lymphocytes. Option A is correct as antigens in tissues reach LN via afferent lymphatic vessels. Option C is correct as infection-induced signals can increase blood flow to LN, facilitating lymphocyte migration. Option D is incorrect because the thoracic duct returns lymph back to the bloodstream, not specifically lymphocytes.

Correct Answer: D

Rationale: The correct answer is D because multiple sclerosis (MS) typically affects individuals between 20-50 years old, with the most common age of onset being between 20-40 years. MS is not primarily a disease of older individuals over 65 years. Choices A, B, and C are incorrect because various HLA alleles have been associated with MS susceptibility, females are indeed more at risk for MS than males, and there is a known North-South gradient in MS incidence, with higher rates reported for populations living farther from the equator.

Correct Answer: D

Rationale: Protease inhibitors interfere with the final step in HIV replication, which is the cleavage of the polyprotein into individual functional proteins. Inhibiting protease prevents the formation of mature infectious viral particles. This step occurs after reverse transcription of viral RNA into DNA, making choice D the correct answer. Choices A, B, and C are incorrect because protease inhibitors do not affect the release of new viral particles, processing of gp160, or the proviral stage of HIV replication.