Immunomodulatory Effects of Phytochemicals

Abstract

Plant-derived secondary metabolites -- flavonoids, polyphenols, terpenoids, and alkaloids -- modulate innate and adaptive immune pathways through mechanisms including NF-kappaB suppression, cytokine network rebalancing, and T-cell receptor signal amplification, yet systematic quantification of structure-activity relationships governing immunomodulatory potency across compound classes remains incomplete. This study evaluated 120 purified phytochemicals (flavonoids n = 36; polyphenols n = 28; terpenoids n = 32; alkaloids n = 24) across five immune endpoints -- TNF-alpha inhibition, IL-6 suppression, IL-10 induction, natural killer (NK) cell activation, and CD4+ T-cell proliferation -- in human peripheral blood mononuclear cell (PBMC), RAW264.7 macrophage, and Jurkat T-cell models (Madrid, Spain; 2021-2023). A Phytochemical Immunomodulatory Index (PII) integrating structural complexity, predicted bioavailability, cytokine modulation breadth, selectivity ratio (anti- to pro-inflammatory activity), and in vitro potency (IC50 aggregated across endpoints) predicted in vivo immunosuppression in a murine collagen-induced arthritis model with AUC = 0.881 and Pearson r = +0.84 (p < 0.001; n = 48 compounds validated in vivo), identifying hydroxylation pattern at the B-ring of flavonoids and methylenedioxy substitution in terpenoids as the principal structural determinants of selective anti-inflammatory activity without concurrent immunosuppression of NK cell cytotoxicity.