Which of the following is a molecule that inhibits T cell activation, is highly expressed in Tregs and is used in a recombinant (synthetic) form to treat some autoimmune diseases?

Correct Answer: B

Rationale: The correct answer is B: CTLA-4. CTLA-4 inhibits T cell activation by binding to CD80/CD86 on antigen-presenting cells, preventing the co-stimulatory signal required for T cell activation. It is highly expressed in Tregs, which suppress immune responses. Recombinant CTLA-4 (e.g., abatacept) is used to treat autoimmune diseases by blocking T cell activation. Explanation for other choices: A: CD86 is a co-stimulatory molecule that activates T cells, not inhibits them. C: MHC class II molecules present antigens to T cells, they do not inhibit T cell activation. D: CD4 is a co-receptor that helps T cells recognize antigens presented by MHC class II molecules, it does not inhibit T cell activation.

Correct Answer: D

Rationale: The correct answer is D because monoclonal antibodies have the ability to block the proliferation of cancer cells by targeting specific antigens on the cancer cells. They can also target cancer cells for destruction through various mechanisms such as antibody-dependent cell-mediated cytotoxicity. Additionally, monoclonal antibodies can inhibit inflammatory immune responses by neutralizing pro-inflammatory mediators or blocking immune cell activation pathways. Therefore, all the options A, B, and C are correct, making D the correct answer.

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.