BACKGROUND: Human periodontal stem cells have a certain inhibitory effect on the pro-inflammatory function of M1-type macrophages, and it is not clear whether icariin, which has anti-inflammatory and other pharmacological activities, can enhance the inhibitory effect of human periodontal stem cells on M1- type macrophages. OBJECTIVE: To investigate the effect of icariin on M1 macrophages after pretreatment of human periodontal stem cells. METHODS: Primary human periodontal stem cells were isolated, cultured and characterized. THP-1 was induced and M1-type macrophages were identified by immunofluorescence staining and PCR. Human periodontal stem cells were cultured with α-MEM complete medium containing concentrations of 10-7, 10-6, 10-5, and 10-4 mol/L icariin, and the cytotoxicity of Icariin on human periodontal stem cells was detected by the CCK-8 assay at 1, 3, 5, and 7 days, respectively. α-MEM complete medium, untreated α-MEM conditioned medium for human periodontal stem cells and α-MEM conditioned medium for human periodontal stem cells pretreated with icariin for 24 hours were conditioned with RPMI-1640 complete medium in a 1:1 ratio for M1-type macrophages in the control, untreated, and pretreated groups, and 24 hours later, the mRNA expression of inflammatory factors in M1 macrophages was detected by RT-PCR. The protein expression of inflammatory factors in M1 macrophages was detected by ELISA. The expression of surface markers and nuclear factor-κB pathway-related proteins in M1/ M2 macrophages was detected by western blot assay. RESULTS AND CONCLUSION: CCK-8 assay results showed that 10-7, 10-6, 10-5, 10-4 mol/L icariin was not cytotoxic to the human periodontal stem cells, and from day 5 onwards, all the concentrations increased the cell viability, and promoted the cell proliferation. 10-4 mol/L icariin was selected for follow-up experiment. RT-PCR and ELISA results showed that compared with the control group, the untreated group and the pretreated group both decreased the expression and secretion of interleukin-1β, interleukin-6, and tumor necrosis factor-α of M1-type macrophages (P < 0.05), and the pretreated group was lower than the untreated group (P < 0.05). Western blot assay results showed that compared with the untreated group, the expression of CD86 was significantly lower in the pretreated group (P < 0.05); compared with the control group, the expression of CD206, a surface marker of M2-type macrophages, was elevated in both the untreated and pretreated groups (P < 0.01), and it was significantly higher in the pretreated group than in the untreated group (P < 0.01). In M1- type macrophages after 24 hours of conditioned culture, compared with the control group, the expression of nuclear factor-κB/P65 was decreased in the untreated group and the pretreated group (P < 0.01), and the expression of p-IκBα was decreased only in the pretreated group (P < 0.01); the expression of both nuclear factor-κB/P65 and p-IκBα was significantly reduced in the pretreated group compared with the untreated group (P < 0.05), while the difference of IκBα in the three groups was not statistically significant. These results indicated that icariin enhanced the inhibitory effect of human periodontal stem cells on M1-type macrophages, and this effect may be related to the inhibition of the nuclear factor-κB signaling pathway of macrophages. [ABSTRACT FROM AUTHOR]