Quercetin as a Potent Modulator of Innate and Adaptive Immunity: An In Vivo Evaluation in Wistar Rats

Background: The immune system maintains host defines through coordinated innate and adaptive responses, and its imbalance can lead to increased susceptibility to infections and inflammatory disorders. Plant-derived flavonoids have attracted attention for their potential immunomodulatory properties. Quercetin, a naturally occurring flavonoid, has shown anti-inflammatory and antioxidant effects, but its effect on different arms of the immune response requires further experimental evaluation. Aim: The aim of the current study was to examine the effect of quercetin on immune system modulation. Methods: Quercetin suspension was administered orally to rats at dose levels of 50,100 and 150mg/kg for 21days. The carbon clearance test, Delayed Type Hypersensitivity (DTH) reaction, and Hemagglutination Antibody (HA) titer were used to examine the immunomodulatory effect on both specific and non-specific immunity. Rats were given cyclophosphamide (100mg/kg p.o.) as an immunosuppression agent. In the processes of delayed type hypersensitivity response and hemagglutinating antibody titers, Sheep Red Blood Cells (SRBCs) were used as an antigen (0.1mL 20% SRBCs). Results: Quercetin significantly reduced antibody titers in response to the SRBC antigen. When compared to the negative control, the immunosuppressed group receiving quercetin showed a significant reduction in first and second HA titers. When immunosuppressed rats were treated with quercetin and pre-sensitized with SRBC antigen, the DTH response was significantly reduced. Quercetin significantly reduced the phagocytic index as compared to the control group, showing that the reticuloendothelial system is inhibited. Conclusion: The study found that quercetin inhibits both targeted and nonspecific immune responses. By reducing leucocyte recruitment, chemokine levels, and levels of the lipid peroxidation end-product malondialdehyde, quercetin decreased the histological signs of acute inflammation in the treated rat in a dose-dependent way. Major Findings: The study demonstrated that quercetin exerts a significant immunomodulatory effect by influencing humoral, cell-mediated, and non-specific immune responses, enhanced antibody and phagocytic responses, and reduced inflammation, showing dose-dependent immunomodulatory potential. These findings suggest that quercetin may have therapeutic potential in conditions involving immune dysregulation and immunosuppression.