What is a primary characteristic of modern immunology?

Correct Answer: B

Rationale: The correct answer is B because modern immunology indeed builds on the groundbreaking contributions of scientists like Jenner and Pasteur. Their work laid the foundation for understanding concepts like vaccination and immune responses. Choice A is incorrect because modern immunology encompasses both innate and adaptive immunity. Choice C is incorrect as immunology extends beyond tissue healing to include immune responses to pathogens and self-cells. Choice D is incorrect as immunology is a rapidly evolving field with significant advancements in understanding immune mechanisms and developing new treatments.

Correct Answer: B

Rationale: Pattern recognition receptors (PRRs) identify Pathogen-associated molecular patterns (PAMPs) because PAMPs are unique molecules found on pathogens that trigger an immune response. PRRs recognize these patterns to distinguish between self and non-self. This recognition is crucial for initiating an immune response against potential threats. Specific antigens (A) and specific viruses only (D) are too narrow in scope as PRRs are designed to detect a wide range of patterns. Host self-proteins (C) are recognized by other mechanisms in the immune system to prevent autoimmunity.

Correct Answer: B

Rationale: Natural killer (NK) cells target virus-infected and cancerous cells because they have the ability to recognize abnormal cells through activating receptors. These cells can identify changes in surface markers associated with viral infection or cancer, leading to their destruction. NK cells do not target bacterial cells (choice A), plasma cells (choice C), or self-antigens (choice D) as these are not typically recognized as threats by the immune system. NK cells play a crucial role in immune surveillance against abnormal cells, making choice B the correct answer.

Correct Answer: C

Rationale: The correct answer is C, Lectin pathway. MBL recognizes pathogen-associated molecular patterns containing mannose, initiating the lectin pathway. MBL binds to mannose on microbial surfaces, activating MBL-associated serine proteases, leading to the formation of the C3 convertase. This triggers the rest of the complement cascade. A: Alternative pathway is triggered by spontaneous hydrolysis of C3, not by MBL. B: Classical pathway is activated by antigen-antibody complexes, not MBL. D: Terminal pathway (also known as the membrane attack complex) is the final step of all complement pathways, not specifically triggered by MBL.

Correct Answer: B

Rationale: The primary role of phagocytosis in innate immunity is to engulf and digest pathogens. Phagocytes such as macrophages and neutrophils recognize and engulf bacteria, viruses, and other harmful substances to prevent infections. They digest these pathogens using enzymes and destroy them. This process is crucial in the initial defense against infections. Option A is incorrect because phagocytosis primarily targets pathogens, not cancer cells. Option C is incorrect because producing antibodies is a function of adaptive immunity, not innate immunity. Option D is incorrect because activating complement proteins is a separate mechanism in the immune response.