An Enzyme-Linked Immunosorbent Assay-Based Method for Functional Analysis of the Three Pathways of the Complement System

The complement system has a crucial role in innate immune defense against invading microorganisms and can be activated by the classical pathway (CP), the alternative pathway (AP), and the mannose-binding lectin (MBL) pathway (MP). The CP is activated by binding of C1q to, e.g., immunoglobulins present on microorganisms or by direct binding to apoptotic cells. The AP can be directly activated by invading microorganisms. The MP is also directly activated, via carbohydrate moieties present on the surface of invading microbes. For assessment of the functional activity of the classical and alternative pathways, hemolysis of erythrocytes by complement activation via either the CP (CH50) or the AP (AP50) is used in most laboratories. The methods to assess pathway activity of the CP, AP, and MP are enzyme-linked immunosorbent assay (ELISA)-based. All three assays are delivered as one ELISA system. Blood samples are to be collected under sterile conditions in red-top tubes, without serum separator. A positive control is provided in the kit. Frozen sera is partially thawed by briefly placing them in a 37№ C water bath with gentle mixing. With the combined assay, the functional activity of the three pathways of complement activation can be assessed. With the use of combined ELISA system, the three pathways for complement activation can be assessed at the same time.