During the course of an immune response to a given antigen, affinity maturation results in survival of:

Correct Answer: B

Rationale: Rationale: 1. Affinity maturation is the process where B cells produce antibodies with increased affinity for the antigen over time. 2. B cells whose antibodies bind the antigen more strongly have higher affinity. 3. Survival of B cells with higher affinity antibodies is crucial for effective immune response. 4. A is incorrect as rate of antibody secretion doesn't necessarily correlate with affinity. 5. C is incorrect as T cells are not directly involved in affinity maturation of antibodies. 6. D is incorrect since T cells are not affected by affinity maturation in the context of this question.

Correct Answer: C

Rationale: Step-by-step rationale: 1. Hybridoma is a cell line formed by the fusion of a B cell (producing a specific antibody) and a myeloma cell. 2. Choice C is correct because hybridomas can be immortalized and cultured indefinitely. 3. Choice A is incorrect because hybridomas produce monoclonal antibodies, not polyclonal antibodies. 4. Choice B is incorrect because hybridomas are formed from a single B cell and a myeloma cell, not two antigen-activated B cells. 5. Choice D is incorrect as only option C accurately describes a hybridoma's characteristic of indefinite tissue culture survival.

Correct Answer: D

Rationale: The correct answer is D because CD8+ T cells are not responsible for antibody-dependent cell-mediated cytotoxicity. A is correct as CD8+ T cells differentiate into cytotoxic T cells. B is correct as CD8+ T cells recognize peptide antigens with MHC molecules. C is correct as CD8+ T cells are vital in defense against intracellular pathogens. D is incorrect as CD8+ T cells do not mediate cell cytotoxicity through antibodies.

Correct Answer: A

Rationale: The correct answer is A. Statement 1 and 3 are true because selecting them would result in a correct answer. Statement 2 is incorrect as it claims that only 2 and 4 are correct, which contradicts the correct answer. Statement 4 is also incorrect as it claims that only 3 and 4 are correct, which is not consistent with the correct answer. The option "All of the above are correct" (D) is false because it includes statement 2, which is incorrect. Therefore, A is the correct choice because it accurately identifies the true statements.

Correct Answer: A

Rationale: Step-by-step rationale: 1. Nuvaxovid is not a known Covid-19 vaccine. 2. Covovax and Moderna are both established Covid-19 vaccines. 3. "None of the above" includes all listed options, so it is not the correct answer. 4. Therefore, the correct answer is A: Nuvaxovid, as it is not a recognized Covid-19 vaccine.