Which cell type is a sentinel in the tissues and part of the innate immune system?

Correct Answer: B

Rationale: The correct answer is B: Dendritic cells. Dendritic cells are sentinel cells in tissues that detect pathogens and activate the immune response. They are crucial in initiating adaptive immune responses by presenting antigens to T cells. T lymphocytes (A) are involved in adaptive immunity, not innate immunity. B lymphocytes (C) mature into plasma cells (D) which produce antibodies, but they are not sentinel cells in tissues like dendritic cells.

Correct Answer: B

Rationale: The correct answer is B because hosts developing epigenetic changes for immune adaptation is a significant consequence of the evolutionary arms race between hosts and pathogens. This adaptation allows hosts to better defend against evolving pathogens over time. This process is dynamic, as both hosts and pathogens continuously evolve in response to each other. Choice A is incorrect because pathogens can evolve rapidly to adapt to host defenses. Choice C is incorrect because while hosts may have mutations that provide advantages, pathogens can also evolve to overcome host defenses. Choice D is incorrect as the interaction between hosts and pathogens is characterized by constant adaptation and change, not remaining static.

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.