Which of the following statements is NOT true

Correct Answer: B

Rationale: The correct answer is B because vaccines using attenuated HIV virus are not in a "phase II" clinical trial. Attenuated virus vaccines are risky due to potential reversion to virulence. A: True, Sub-Saharan Africa has the highest HIV prevalence. C: CD4+ counts decline during clinical latency. D: Viral RNA titer increases in the final stages.

Correct Answer: D

Rationale: Step-by-step rationale for why answer D is correct: 1. Crohn's disease is characterized by chronic inflammation in the gastrointestinal tract. 2. It is associated with dysregulation of the immune response to gut flora. 3. Overgrowth of gut commensal flora can trigger and exacerbate inflammation in Crohn's disease. 4. Choices A, B, and C do not directly relate to the pathophysiology of Crohn's disease, making them incorrect.

Correct Answer: D

Rationale: The correct answer is D because flu neuraminidase is a surface protein that allows the release of newly formed viral particles and it is also the target of Tamiflu. Neuraminidase helps the virus spread by cleaving sialic acid from host cells, facilitating the release of viral particles. Tamiflu inhibits neuraminidase, preventing the spread of the virus. Option A is incorrect because neuraminidase does not directly help the virus escape the host immune response. Option B is partially correct but incomplete without mentioning Tamiflu. Option C is also partially correct but incomplete without mentioning the role of neuraminidase in releasing viral particles.

Correct Answer: D

Rationale: The correct answer is D because coupling the polysaccharide subunit to a protein carrier enhances the immune response by converting the T-independent response to a T-dependent response. This allows for the induction of memory B cells and long-lasting immunity. Adjuvants (choice A) may enhance immune response but are not essential for polysaccharide-protein conjugate vaccines. Multiple booster injections (choice B) are not required for polysaccharide-protein conjugate vaccines as a single dose can induce a robust immune response. Administering orally (choice C) is not the only route for obtaining an immune response to polysaccharide subunit vaccines.

Correct Answer: D

Rationale: The correct answer is D, "All of the above." T cells help B cells undergo isotype switching by providing cytokines. They also help B cells produce antibodies against protein antigens by activating them. T cells provide signal 2 of activation to B cells through the interaction of CD40 on B cells with CD40L on T cells. Therefore, all of these functions are critical for the collaboration between T and B cells in the immune response.