What are the three main principles of adaptive immunity?

Correct Answer: B

Rationale: The three main principles of adaptive immunity are Recognize, Respond, Remember. 1. Recognize: Immune system identifies specific pathogens through antigen recognition. 2. Respond: Immune response is triggered to eliminate the pathogen. 3. Remember: Immune system forms memory cells for faster and stronger response upon re-exposure. Other options are incorrect: A: Respond, Replace, Repair - Incorrect as it does not reflect the key processes of adaptive immunity. C: Resist, Retain, Recruit - Incorrect as these terms do not accurately describe the adaptive immune response. D: React, Replicate, Restore - Incorrect as it does not encompass the essential principles of adaptive immunity.

Correct Answer: B

Rationale: The correct answer is B: Thymus. T cells mature in the thymus, where they undergo selection and maturation processes essential for their function in the immune system. The thymus provides a specialized environment for T cell development, including positive and negative selection to ensure self-tolerance and functional T cell repertoire. A: Bone marrow is incorrect because it is the site of B cell maturation, not T cells. C: Spleen is incorrect as it acts as a secondary lymphoid organ for immune response but not the site of T cell maturation. D: Lymph nodes are incorrect as they are important for immune surveillance and activation but not the primary site for T cell maturation.

Correct Answer: B

Rationale: The correct answer is B: IgA. IgA is primarily involved in mucosal immunity as it is the most abundant antibody present in mucosal secretions like saliva, tears, and breast milk. IgA plays a crucial role in preventing pathogens from entering the body through mucosal surfaces. IgG is more involved in systemic immunity, IgM is the first antibody produced in response to an infection, and IgE is associated with allergic reactions. Therefore, IgA is the most appropriate choice for mucosal immunity.

Correct Answer: D

Rationale: The correct answer is D: Type IV hypersensitivity. This type is mediated by T cells, specifically CD4+ helper T cells and CD8+ cytotoxic T cells. The process involves antigen-presenting cells activating T cells, leading to a delayed response. Choices A, B, and C involve different mechanisms and are not mediated by T cells. Type I is mediated by IgE antibodies, Type II involves antibody-mediated cell destruction, and Type III involves immune complex deposition. Therefore, Type IV is the only hypersensitivity type directly mediated by T cells.

Correct Answer: C

Rationale: The correct answer is C: Systemic lupus erythematosus (SLE). In Type III hypersensitivity, immune complexes form and deposit in tissues, leading to inflammation and tissue damage. SLE is a classic example of a Type III hypersensitivity reaction where these immune complexes deposit in various organs causing systemic inflammation and damage. Graves's disease (A) is an example of Type II hypersensitivity, where autoantibodies target cell-surface receptors. Goodpasture's syndrome (B) is a Type II hypersensitivity disease affecting the kidneys and lungs. Contact dermatitis (D) is a Type IV hypersensitivity reaction mediated by T cells, not involving immune complexes. Therefore, the correct answer is C as it aligns with the characteristic disease associated with Type III hypersensitivity.