Which assay assesses the functional activity of the classical pathway?

Which assay assesses the functional activity of the classical pathway?

• A. CH50
• B. AH50
• C. Radial immunodiffusion
• D. Lytic assay with liposome

Answer: (A)

The idea being tested is how to measure the functional activity of the classical complement pathway. CH50 is the classic hemolytic assay for this purpose: patient serum is tested for its ability to lyse antibody-sensitized sheep red blood cells. If the classical pathway is working, the antibody-coated targets trigger C1 and the downstream cascade (C4, C2, and beyond) to form the membrane attack complex and lyse the cells. The CH50 titer reflects the serum dilution that achieves 50% lysis; a low CH50 indicates a deficiency or inhibition of classical pathway components, whereas a normal CH50 means the classical pathway is functionally intact. By comparison, AH50 specifically tests the alternative pathway’s ability to drive lysis without antibodies, radial immunodiffusion measures concentrations of immunoglobulins or antigens rather than pathway function, and a liposome lytic assay assesses general membrane-attack complex activity but isn’t specific to the classical activation route.

The idea being tested is how to measure the functional activity of the classical complement pathway. CH50 is the classic hemolytic assay for this purpose: patient serum is tested for its ability to lyse antibody-sensitized sheep red blood cells. If the classical pathway is working, the antibody-coated targets trigger C1 and the downstream cascade (C4, C2, and beyond) to form the membrane attack complex and lyse the cells. The CH50 titer reflects the serum dilution that achieves 50% lysis; a low CH50 indicates a deficiency or inhibition of classical pathway components, whereas a normal CH50 means the classical pathway is functionally intact. By comparison, AH50 specifically tests the alternative pathway’s ability to drive lysis without antibodies, radial immunodiffusion measures concentrations of immunoglobulins or antigens rather than pathway function, and a liposome lytic assay assesses general membrane-attack complex activity but isn’t specific to the classical activation route.