Pharmacological activities of flavonoids (III) structure-activity relationships of flavonoids in immunosuppression

Effects of twenty-one different flavonoids and their related compounds on the phagocytosis of colloidal carbon by macrophages in liver and spleen, humoral immune responses against bacterial α-amylase and cellular immune responses against oxazolone and dinitrofluorobenzene were studiedin vivo andin vitro. It was shown that most of the flavonoids accelerated significantly the phagocytosis, and they suppressed significantly not only humoral and cellular immune responses but also the development of immunological memory after the antigenic stimulation. Especially, malvin was the most active in phagocysis, and disodium cromoglycate and morin were the most active in humoral and cellular immunosuppression, respectively. Daidzein had the most potent inhibitory activity in the development of memory cells. The structure-activity relationships of the flavonoids in immunosuppression became apparant from these results: 1. The presence of C_2–3 double bond and C₄ ketone group in C-ring was important for their immunosuppressive activity. 2. Flavonoids with benzene ring at 2 or 3 position in C-ring showed the almost same activities. 3. The opening of C-ring did not affect their immunosuppressive activity. 4. The glycosylated flavonoids at 3 position in C-ring were less potent than their aglycones. 5. Di- or tri-hydroxylated flavonoids in B-ring were more potent than mono-hydroxylated. 6. Chromanochromanone also had the immunosuppressive activity.