How do cytokines typically function in the body?

Correct Answer: B

Rationale: The correct answer is B because cytokines primarily function in an autocrine and paracrine manner. Autocrine signaling occurs when a cell produces a cytokine that acts on the same cell, while paracrine signaling involves cytokines acting on nearby cells. This allows cytokines to regulate immune responses locally. Option A is incorrect as endocrine signaling involves hormones acting on distant target cells via the bloodstream, which is not the primary function of cytokines. Option C is incorrect because cytokines do not require direct contact with pathogens to function. Option D is incorrect as cytokines do not degrade immune cells but rather regulate immune responses.

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.

Correct Answer: B

Rationale: The correct answer is B: Granzyme. Granzyme is the molecule released by NK cells that induces apoptosis in target cells. It enters the target cell through perforin, which creates pores in the target cell membrane. Cytokines are signaling molecules released by various immune cells but do not directly induce apoptosis. Antibodies are produced by B cells and do not induce apoptosis. Perforin aids in the delivery of granzyme but is not responsible for inducing apoptosis itself. Therefore, Granzyme is the correct choice for inducing apoptosis by NK cells.