Macrophages express multiple types of receptors on their surface that stimulate phagocytosis of microbes, leading to pathogen internalization and destruction. Many of these receptors, such as Dectin-1, rely on direct recognition of a PAMP on the pathogen surface. However, some receptors that stimulate phagocytosis rely on soluble factors (not associated with the phagocyte membrane) to identify and mark the pathogen for uptake by the phagocyte. One such receptor is:

Correct Answer: D

Rationale: Complement receptors bind soluble C3b; mannose , scavenger , and lectin receptors bind PAMPs directly.

Correct Answer: A

Rationale: Blood type AB is a universal recipient (general receptor) because it has no antibodies against A, B, or Rh antigens, but it is not a universal donor.

Correct Answer: B

Rationale: Passive immunity involves receiving pre-formed antibodies from another source, not self-production or cell transfer.

Correct Answer: C

Rationale: HIV's high mutation rate creates drug-resistant strains, complicating eradication, not its RNA genome, rare mutation, or size.

Correct Answer: C

Rationale: Zymosan, a fungal cell wall component, is a PAMP, unlike dsRNA (viral), LPS (bacterial), or CpG (bacterial DNA).