Which of the following is a primary lymphoid organ?

Correct Answer: B

Rationale: The correct answer is B: Thymus. The thymus is considered a primary lymphoid organ because it is where T lymphocytes (T cells) mature and differentiate. T cells play a crucial role in the adaptive immune response. The thymus is responsible for educating T cells to recognize self versus non-self antigens. Summary: A: Spleen is a secondary lymphoid organ involved in filtering blood and producing antibodies, not where T cells mature. C: Lymph node is also a secondary lymphoid organ where immune cells interact but not where T cells mature. D: Mucosal immune system refers to the immune system in mucosal tissues, not a specific primary lymphoid organ.

Correct Answer: B

Rationale: The correct answer is B because the immune system plays a crucial role in promoting wound healing and eliminating cell debris. When tissue is damaged, the immune response helps remove dead cells and debris, initiates the healing process, and supports tissue regeneration. This involves the recruitment of immune cells to the site of injury, releasing growth factors to stimulate cell proliferation, and resolving inflammation. Choice A (Preventing pathogen invasion) is incorrect because while the immune system does play a role in preventing pathogen invasion, this is not directly related to tissue regeneration. Choice C (Increasing cytokine production) is incorrect because although cytokines are involved in the immune response and can influence tissue repair, simply increasing cytokine production does not fully describe the immune system's role in tissue regeneration. Choice D (Suppressing adaptive immunity) is incorrect because suppressing adaptive immunity would hinder rather than promote tissue regeneration, as adaptive immunity plays a role in immune memory and long-term protection against pathogens.

Correct Answer: A

Rationale: Paul Ehrlich predicted the existence of antibodies and their ability to bind toxins. He introduced the concept of the side-chain theory, proposing that cells have specific receptors (later known as antibodies) that can bind to toxins and neutralize them. This groundbreaking idea laid the foundation for modern immunology. Ehrlich's work was instrumental in understanding the immune response and paved the way for advancements in vaccine development and disease treatment. Choice B (Discovery of germ theory) is incorrect because it was proposed by Louis Pasteur and Robert Koch, not Paul Ehrlich. Choice C (Smallpox eradication) is incorrect as Ehrlich did not predict smallpox eradication. Choice D (Development of vaccines) is incorrect because while Ehrlich's work contributed to vaccine development, his specific prediction was about antibodies and their toxin-binding ability, not vaccines in general.

Correct Answer: B

Rationale: The correct answer is B: Lipopolysaccharide (LPS). TLR4 recognizes LPS, a component of the outer membrane of Gram-negative bacteria, triggering an immune response. This recognition is crucial in detecting bacterial infections. Peptidoglycan (A) is recognized by other TLRs, not TLR4. Double-stranded RNA (C) is recognized by TLR3, not TLR4. Mannose-binding lectin (D) is a pattern recognition receptor that binds to carbohydrate structures, not specifically recognized by TLR4.

Correct Answer: C

Rationale: Correct Answer: C Rationale: 1. Innate immunity is rapid: It provides immediate defense against pathogens. 2. Innate immunity is non-specific: It reacts in the same way to all pathogens. 3. Adaptive immunity, on the other hand, is slower and pathogen-specific. 4. Adaptive immunity develops memory to provide long-lasting protection. Summary: A: Innate immunity does not develop memory; adaptive immunity does. B: Adaptive immunity may not always be functional due to various factors. D: Adaptive immunity requires activation through exposure to specific antigens.