Which components comprise the classical complement cascade?

• A. Complement Cascade (C3, C4, CH50)
• B. Antibody Titer
• C. C-Reactive Protein
• D. Erythrocyte Sedimentation Rate

Answer: (A)

The classical complement cascade is a chain of serum proteins that become activated in a specific sequence to mediate opsonization, inflammation, and cell lysis. Key components in this pathway are C3 and C4, which participate in the early steps that generate the C3 convertase and propagate the cascade toward the formation of the membrane attack complex. CH50, while not a protein in the cascade itself, is a laboratory test that measures the overall functional activity of the classical pathway, reflecting how well the cascade can proceed from start to finish. Therefore, C3 and C4 are actual components of the cascade, and CH50 represents the cascade’s functional readout. Inflammatory or immune markers like antibody titer, C-reactive protein, and erythrocyte sedimentation rate do not constitute parts of the complement cascade.