What is one of the immune system's critical functions in cancer?

Correct Answer: B

Rationale: The correct answer is B: Fighting cancer by targeting abnormal cells. The immune system plays a crucial role in cancer by identifying and eliminating abnormal cells that can develop into tumors. This process is known as immunosurveillance. Through mechanisms like T cells and natural killer cells, the immune system can detect and destroy cancerous cells before they can grow and spread. This function is essential in preventing the development and progression of cancer. Choices A, C, and D are incorrect: A: Promoting cell growth - The immune system does not promote cell growth in cancer; rather, it regulates and suppresses the growth of abnormal cells. C: Enhancing pathogen resistance - While the immune system does enhance resistance against pathogens, this is not its critical function in cancer. D: Stimulating autoimmune responses - Autoimmune responses involve the immune system attacking healthy cells, not targeting cancerous cells.

Correct Answer: B

Rationale: The correct answer is B - Macrophages and neutrophils are the most important phagocytes in innate immunity. Macrophages are versatile cells that engulf and destroy pathogens, while neutrophils are the most abundant phagocytes in the blood and are critical for early immune responses. Natural killer cells and B lymphocytes (A) are not phagocytes, but rather involved in adaptive immunity. T cells and dendritic cells (C) play roles in adaptive immunity and antigen presentation, not direct phagocytosis. Basophils and eosinophils (D) are involved in allergic reactions and parasitic infections, not primary phagocytic functions.

Correct Answer: C

Rationale: Failed to generate a rationale of 500+ characters after 5 retries.

Correct Answer: B

Rationale: The primary trigger for NK cell activation is the lack of normal self-surface structures. NK cells are part of the innate immune system and recognize cells with altered or missing self-antigens. This triggers their activation to eliminate these abnormal cells. Presence of PAMPs (A) activates other immune cells like macrophages. High levels of complement proteins (C) activate the complement cascade but do not directly trigger NK cell activation. Antigen presentation by dendritic cells (D) activates adaptive immune responses through T cells, not NK cells. Therefore, the correct answer is B as it directly relates to NK cell function.

Correct Answer: C

Rationale: The correct answer is C: C5b. The Membrane Attack Complex (MAC) is formed by a sequence of complement proteins, with C5b playing a crucial role as the initiator. After C5b binds to the target cell membrane, it triggers the assembly of C6, C7, C8, and multiple C9 molecules to form the MAC pore. C1 (A) is the initiator of the classical pathway, not a component of the MAC. C3 (B) is involved in the formation of the C3 convertase and opsonization but is not the main component of the MAC. C4b (D) is part of the classical pathway and is involved in the formation of the C3 convertase, not the MAC.