Objective To explore the effect of Huangqin decoction (HQD) on group 3 innate lymphoid cells (ILC3s) and helper T

cells (Th) for treatment of ulcerative colitis (UC). Methods Male Balb/c mice were randomly divided into control group, DSS group, mesalazine group (ME, 400 mg/kg), and 2.275 g/kg, 4.55 g/kg and 9.1 g/kg HQD groups. All the mice were given free access to normal chow. Except for those in the normal control group, all the mice were given 3% DSS solution for 7 days to establish models of UC. The mice in ME group and 3 HQD groups were given mesalazine or HQD via oral gavage at the specified doses once a day. Flow cytometry was performed to analyze the ILC3s, MHC II, Th1 and Treg in the lamina propria lymphocytes in the colon. Milliplex was performed to determine cytokine levels of in the colon tissues. Results Compared with those in DSS group, the mice in the 3 HQD groups all showed obviously lessened symptoms of UC with significantl decreased DAI score (P<0.001) and macroscopic score (P<0.001). The results of flow cytometry showed that HQD treatment significantly increased the percentage of ILC3s (P<0.05) and expression of MHCⅡ (P<0.05), obviously reduced the proportion of Th1 (P<0.05) but increased Treg cells (P<0.05) in the colon tissues. Milliplex showed that HQD treatment significantly reduced the expressions of Th-related pro-inflammatory cytokines including IL-2 (P<0.05), IL-17A (P<0.05), IL-23 (P<0.05), TNF-α (P<0.05), and IFN- γ (P<0.05). Conclusion HQD alleviates DSS- induced UC in mice by increasing ILC3s and MHC Ⅱ expression to suppress the function of Th17 and Th1 cells and promote Treg and Th2 cells.