B cells express a complement receptor that binds to C3b cleavage products, such as iC3b and C3dg. When a B cell with an antigen receptor that specifically recognizes that pathogen also has its complement receptor stimulated because the pathogen is opsonized with these C3 fragments, B cell activation is greatly enhanced. This mechanism functions to:

Correct Answer: A

Rationale: Complement enhances B-cell detection of pathogens early ; not prevention , phagocytosis , or just replication .

Correct Answer: D

Rationale: Cardiac output is defined as the volume of blood pumped by the heart per minute into the systemic circulation.

Correct Answer: A

Rationale: As of 2012 (document date), no effective AIDS vaccine existed, unlike for polio, measles, and tetanus.

Correct Answer: C

Rationale: HIV infects helper T cells via CD4 receptors, disrupting immune regulation, not cytotoxic T, NK, or memory cells primarily.

Correct Answer: C

Rationale: Perforin forms pores in target cell membranes, allowing granzymes to enter and induce lysis, not related to C9 or MHC detection.