Why don't we have a successful HIV vaccine?

Correct Answer: D

Rationale: The correct answer is D because all the statements in choices A, B, and C are valid reasons why we don't have a successful HIV vaccine. A: HIV has a high mutation rate, making it challenging to generate a protective memory response. B: Inducing mucosal immunity is difficult to block sexual transmission, a common route of HIV infection. C: HIV targets immune cells, which hinders the immune system's ability to mount an effective response. Therefore, all these factors combined pose significant challenges for creating an effective HIV vaccine.

Correct Answer: B

Rationale: The correct answer is B because TH2 cells play a crucial role in protecting against parasitic worms by secreting cytokines that promote eosinophil activation and antibody production. This response helps to expel the parasites from the body. Incorrect choices: A: TH1 cells are responsible for protection against intracellular bacteria. C: TH3 cells, not TH2 cells, are known for secreting anti-inflammatory cytokines. D: Activation of macrophages is primarily mediated by TH1 cells through IFN-gamma secretion.

Correct Answer: B

Rationale: The correct answer is B because lysozyme is not a type of defensin. Lysozyme is an enzyme present in secretions and tears, part of chemical innate barriers to infection, and capable of dissolving the cell wall of bacteria. Defensins are a different type of antimicrobial peptides that function by disrupting the microbial cell membrane. Therefore, B is the correct answer as it does not accurately describe lysozyme's function.

Correct Answer: D

Rationale: Pattern recognition receptors (PRRs) are a class of receptors that recognize specific molecular patterns associated with pathogens. They can be found in various locations within the body, including in soluble form in the blood (Choice A), in the cytosol of cells (Choice B), and on endosomal membranes (Choice C). Therefore, the correct answer is D, "All of the above are correct," as PRRs can indeed be located in all of these locations. PRRs play a crucial role in the innate immune response by detecting and responding to pathogens, making their presence in multiple cellular compartments essential for effective immune surveillance and defense.

Correct Answer: D

Rationale: The correct answer is D, "All of the above." Mast cells, eosinophils, and basophils are all involved in allergic reactions. Mast cells release histamine, leading to inflammation. Eosinophils are involved in allergic responses and parasitic infections. Basophils release histamine and other inflammatory mediators. Therefore, all three cell types play a crucial role in allergic reactions. Choices A, B, and C alone are incorrect because each cell type individually participates in allergic reactions.