Which method is used to measure an individual complement component rather than the function of a pathway?

Which method is used to measure an individual complement component rather than the function of a pathway?

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

Answer: (C)

In testing the complement system, you can distinguish between functional assays that measure how well a pathway works and quantitative assays that determine how much of a specific component is present. The method that measures an individual complement component is radial immunodiffusion. In this technique, a specific antibody is embedded in an agarose gel and a sample containing the target component diffuses out from a well. The component forms a visible precipitation ring with the antibody, and the ring diameter is proportional to the concentration of that component. This allows direct quantification of a single component such as C3 or C4, independent of the overall pathway activity. Functional assays like CH50 assess the ability of serum to lyse antibody-sensitized red blood cells, reflecting the entire classical pathway’s function; AH50 does the same for the alternative pathway. A lytic assay with liposomes measures membrane attack complex–mediated lysis, again a functional readout rather than a specific component’s amount. So radial immunodiffusion uniquely provides a quantitative measure of an individual complement component rather than the function of a whole pathway.

In testing the complement system, you can distinguish between functional assays that measure how well a pathway works and quantitative assays that determine how much of a specific component is present. The method that measures an individual complement component is radial immunodiffusion. In this technique, a specific antibody is embedded in an agarose gel and a sample containing the target component diffuses out from a well. The component forms a visible precipitation ring with the antibody, and the ring diameter is proportional to the concentration of that component. This allows direct quantification of a single component such as C3 or C4, independent of the overall pathway activity.

Functional assays like CH50 assess the ability of serum to lyse antibody-sensitized red blood cells, reflecting the entire classical pathway’s function; AH50 does the same for the alternative pathway. A lytic assay with liposomes measures membrane attack complex–mediated lysis, again a functional readout rather than a specific component’s amount. So radial immunodiffusion uniquely provides a quantitative measure of an individual complement component rather than the function of a whole pathway.