Dietary Flavonoids as Potential Natural Biological Response Modifiers Affecting the Autoimmune System

In vitro anti‐complement activity of 19 phenolic compounds was evaluated in the classical pathway. Two flavonoids, epigallocatechin gallate and myricetin, exhibited marked anti‐complement activities with IC 50 values of 4.2 and 5.2 μg/mL (concentration causing 50% inhibition of complement activity), respectively. The two flavonoids appeared to interact with both antibody‐sensitized erythrocytes and complement components to inhibit the cascade reactions in the classical pathway of the complement system. The flavonoids may function as natural biological response modifiers by multiple mechanisms including anticomplement effects. Dietary flavonoids may thus affect the body's autoimmune system.