Which statement describes a true function of the complement system?

Which statement describes a true function of the complement system?

• A. Lysis of foreign cells.
• B. Decreased phagocytosis.
• C. Inactivation of antibodies.
• D. Suppression of inflammation.

Answer: (A)

The complement system can directly destroy invading cells by forming the membrane attack complex, which inserts pores into the target’s membrane and causes lysis. This is a primary way complement acts as an immediate effector, especially against bacteria and other pathogens. That’s why the statement about lysis is correct: the MAC-mediated lysis is a distinct and well-established function of the complement cascade, complementary to opsonization and inflammation that help coordinate the broader immune response. The other ideas don’t fit because complement activation actually enhances phagocytosis through opsonization (not decreases it), helps clear immune complexes rather than inactivating antibodies, and promotes inflammation rather than suppressing it (via mediators like C3a and C5a).

The complement system can directly destroy invading cells by forming the membrane attack complex, which inserts pores into the target’s membrane and causes lysis. This is a primary way complement acts as an immediate effector, especially against bacteria and other pathogens.

That’s why the statement about lysis is correct: the MAC-mediated lysis is a distinct and well-established function of the complement cascade, complementary to opsonization and inflammation that help coordinate the broader immune response.

The other ideas don’t fit because complement activation actually enhances phagocytosis through opsonization (not decreases it), helps clear immune complexes rather than inactivating antibodies, and promotes inflammation rather than suppressing it (via mediators like C3a and C5a).