Which statement best describes the pathways that activate the complement system?

Which statement best describes the pathways that activate the complement system?

• A. Only the classical pathway can activate complement.
• B. Only the lectin pathway can activate complement.
• C. Both classic and lectin pathways can trigger complement activation.
• D. The alternative pathway is the sole activator.

Answer: (C)

Complement activation can be triggered by more than one route, each recognizing different signals on microbes or immune complexes. The classical pathway starts when antibodies bound to an antigen recruit C1 and kick off the proteolytic cascade. The lectin pathway is activated when mannose-binding lectin (or related proteins) binds to carbohydrate patterns on the pathogen surface, starting a cascade similar to the classical pathway. Both of these routes converge on the formation of C3 convertases, amplifying the response and leading to opsonization, inflammation, and microbial lysis. The alternative pathway also activates complement directly on microbial surfaces through spontaneous C3 hydrolysis and subsequent steps, providing antibody-independent activation. Among the given choices, recognizing that both the classical and lectin pathways can initiate complement activation accurately reflects the multiple recognition routes that can start this cascade, even though an additional route exists as well.

Complement activation can be triggered by more than one route, each recognizing different signals on microbes or immune complexes. The classical pathway starts when antibodies bound to an antigen recruit C1 and kick off the proteolytic cascade. The lectin pathway is activated when mannose-binding lectin (or related proteins) binds to carbohydrate patterns on the pathogen surface, starting a cascade similar to the classical pathway. Both of these routes converge on the formation of C3 convertases, amplifying the response and leading to opsonization, inflammation, and microbial lysis. The alternative pathway also activates complement directly on microbial surfaces through spontaneous C3 hydrolysis and subsequent steps, providing antibody-independent activation. Among the given choices, recognizing that both the classical and lectin pathways can initiate complement activation accurately reflects the multiple recognition routes that can start this cascade, even though an additional route exists as well.