Immunomodulatory properties of plant polyphenols shown in an <i>in vitro</i> experimental model

Abstract

Polyphenols exert a wide range of biological effects, including immunomodulatory action. Studying the effects of flavonoids on phagocytic activity of specialized phagocytic cells seems to be a rather promising direction for their further usage as pharmacological (therapeutic) agents. Quercetin and luteolin are the most commonly studied flavonoid substances with pleiotropic action. In-depth study and understanding of immunotropic mechanisms (e.g., regulation of phagocytosis) is a prerequisite for adequate pharmacotherapy in infectious conditions, nonspecific inflammatory diseases, autoimmune and oncological disorders. The aim of our work is to study the effect of flavonoids upon phagocytic activity of professional phagocytes (neutrophils) using an in vitro test system. The biological material (venous blood) from 30 practically healthy people (adults n = 15, children n = 15) was used in the present work. The study was carried out in accordance with established international regulations. 0.5 mg/L of Luteolin (basic substance content ≥ 98%) and Quercetin (basic substance content ≥ 95%) were added to experimental samples and incubated for 20 min at 37 °С. The percentage of phagocytosis, phagocytic number (mean number of formalin-treated sheep erythrocytes engulfed per one neutrophil) was determined in control and experimental samples using light microscopy. The unidirectional nature of phagocytosis inhibition by quercetin and luteolin was noted in the test experiments. A statistically significant (p < 0.05) decrease in the phagocytosis intensity by 10% was shown in experimental blood samples obtained from adult patients compared with control values. When quercetin and luteolin were added to blood samples obtained from children, a statistically significant (p < 0.05) decrease in phagocytosis by 30% was noted against control values. At the same time, the mean percentage of phagocytosis and phagocytic number in blood samples after the addition of flavonoids were found to be in the range of reference values, thus suggesting adequacy and physiological suppression of excessive activities of innate immunity compartments by quercetin and luteolin. At this concentration, the flavonoids were found to exert a more pronounced suppressive effect on phagocytic activity in children. Modeling of immune response using the phagocytosis indices assayed in experimental in vitro models with neutrophils from practically healthy adults and children enables us to expand the knowledge of mechanisms underlying the immunotropic effects of flavonoids (quercetin and luteolin), in order to correct immunopathological conditions.