TLR-3 detects viruses found in:

Correct Answer: C

Rationale: TLR-3 detects viruses in endosomes. When a virus enters a host cell, it is often engulfed into endosomes. TLR-3 recognizes viral RNA within endosomes and triggers an immune response. Choices A and B are incorrect because TLR-3 does not detect viruses in the cytosol or extracellular space. Choice D is incorrect because TLR-3 specifically functions in endosomes to detect viral RNA.

Correct Answer: B

Rationale: The correct answer is B. Herd immunity refers to the protection offered to non-immunized individuals when a high percentage of the population is immunized, preventing the pathogen from spreading easily. This is because when a large portion of the population is immune to a disease, it creates a barrier that reduces the overall transmission of the pathogen, thus protecting those who are not vaccinated or cannot be vaccinated. Choice A is incorrect because herd immunity is not solely about the total number of immunized individuals, but rather about the impact on the entire population. Choice C is incorrect as it refers to the efficacy of the vaccine in generating a protective response, not the concept of herd immunity. Choice D is incorrect as it relates to social influence rather than the collective protection provided by high rates of immunization.

Correct Answer: A

Rationale: Rationale: 1. FOXP3 gene encodes a transcription factor crucial for regulatory T cells function. 2. Mutations in FOXP3 lead to dysfunctional regulatory T cells, causing autoimmune disorders. 3. Scurfy phenotype matches the symptoms of autoimmune disorders seen with FOXP3 mutations. Summary: - B (AIRE): AIRE mutations cause autoimmune polyendocrine syndrome, not scurfy phenotype. - C (NFkB): NFkB is a transcription factor involved in immune response but not linked to scurfy phenotype. - D (IRF): IRF is a regulator of interferon signaling, not directly associated with scurfy phenotype.

Correct Answer: D

Rationale: The correct answer is D because secondary lymphoid tissues are where both A and C processes occur. Naïve lymphocytes become activated in secondary lymphoid tissues through interactions with antigens, leading to their differentiation into effector cells. Somatic hypermutation also occurs in secondary lymphoid tissues, specifically in germinal centers of lymph nodes, leading to the generation of high-affinity antibodies. Option B, VDI gene rearrangement, does not occur in secondary lymphoid tissues; it is a process that happens in the primary lymphoid organs (bone marrow and thymus) during the development of lymphocytes. Thus, options A and C are correct, making the correct answer D.

Correct Answer: A

Rationale: The correct answer is A because during clonal selection, lymphocytes specific to the pathogen are activated, leading to their proliferation and differentiation into effector cells. This results in an increase in the number of lymphocytes specific for the pathogen, enhancing the immune response. Choice B is incorrect because clonal selection does not involve the elimination of non-specific lymphocytes but rather the expansion of specific lymphocytes. Choice C is also incorrect because clonal selection does not change the antigen receptor specificities expressed by lymphocytes but instead focuses on expanding the population of lymphocytes with receptors specific to the pathogen. Therefore, the correct outcome of clonal selection is the increase in the number of lymphocytes specific for the pathogen that activated the response, making choice A the most accurate option.