The CH50 assay is a traditional clinical assay that measures the function of complement components. In a CH50 assay patient blood is drawn and serum separated from it (serum has no cells). Patient serum is mixed with antibody-coated sheep red blood cells[1]. The ability of the patient's serum to lyse the sheep red blood cells is then measured.

In the AH50 assay a similar test is performed but the blood cells used do not have antibody coating them. Basically the patient's serum is mixed with an animal's red blood cells (no antibodies present). The ability of the patient's serum to lyse the red blood cells is then measured.

Question: Which pathway of complement activation does the CH50 assay measure? Which pathway does the AH50 assay measure? Explain your answer

[1] In the CH50 assay sheep red blood cells are coated with antibody because this combination (cell + antibodies) can potentially trigger complement activation. The antibodies used in this assay would interact with complement components in the patient sera the same way the patient's own antibodies would.