Quercetin is a herbal flavonoid derived from various foods of plant origin and plays a role in anti-inflammation.Although a number of researches in the field have been done,the mechanism of anti-inflammatory effect ofquercetin should be further clarified.In the present study,we investigated the effects of quercetin on IL-6production by LPS-stimulated neutrophils in human.Neutrophils were were pre-treated with quercetin at the finalconcentrations of ranging from 0-80 μM for 30 min,or not treated,and then incubated in the presence or absenceof lipopolysaccharide(LPS)at a final concentration of 100 ng/ml for indicated time.The secretion level of IL-6 inthe culture supernatants was assayed by ELISA,the intracellular level of IL-6 was detected by flow cytometry andthe expression of IL-6 mRNA was analyzed by RT-PCR.The experiment results showed that neutrophils culturedwith medium or quercetin alone did not express IL-6,but LPS(100 ng/ml)induced IL-6 expression of neutrophils.However,after pre-treatment of neutrophils with quercetin(40 μM)for 30 min,the inducible effects of LPS on theincrease of IL-6 secretion,intracellular IL-6 level and IL-6 mRNA expression by neutrophils were abrogated.IL-6is one of the important pro-inflammatory factors,especially in early phage of inflammation.Thus,our datasuggested that quercetin might exert its anti-inflammatory effect through negatively modulating pro-inflammatoryfactors,such as IL-6.The inhibitory effects of quercetin on IL-6 production by neutrophils may provide atheoretical basis on future therapy of inflammation.Cellular & Molecular Immunology.2005;2(6):455-460. Quercetin is a herbal flavonoid derived from various foods of plant origin and plays a role in anti-inflammation.Although a number of researches in the field have been done,the mechanism of anti-inflammatory effect ofquercetin should be further clarified.In the present study ,we investigated the effects of quercetin on IL-6production by LPS-stimulated neutrophils in human.Neutrophils were were pre-treated with quercetin at the finalconcentrations of ranging from 0-80 μM for 30 min, or not treated,and then incubated in the Presence or absence of lipopolysaccharide (LPS) at a final concentration of 100 ng/ml for indicated time.The secretion level of IL-6 in the culture supernatants was assayed by ELISA, the intracellular level of IL-6 was detected by flow cytometry and the expression of IL-6 mRNA was analyzed by RT-PCR.The experiment results showed that neutrophils culturedwith medium or quercetin alone did not express IL-6,but LPS(100 ng/ml)induced IL-6 expression of neutrophils.However,after Pre-treatment of neutrophils with quercetin(40 μM) for 30 min,the inducible effects of LPS on theincrease of IL-6 secretion,intracellular IL-6 level and IL-6 mRNA expression by neutrophils were abrogated.IL-6is one of the Important pro-inflammatory factors,especially in early phage of inflammation.Thus,our datasuggested that quercetin might exert its anti-inflammatory effect through negatively modulating pro-inflammatoryfactors,such as IL-6.The inhibitory effects of quercetin on IL-6 production by Neutrophils may provide atheoretical basis on future therapy of inflammation. Cellular & Molecular Immunology. 2005;2(6):455-460.