Objective To preliminarily evaluate the effect of levocetirizine hydrochloride at different concentrations on the growth of in vitro cultured human dermal papilla cells,and to explore its mechanism.Methods Human dermal papilla cells were divided into several groups to be cultured with Dulbecco's modified eagle medium (DMEM) containing 0 (control group),1,10,100,1 000,10 000 μg/L levocetirizine hydrochloride respectively for 48 hours.Immunofluorescence staining was performed to observe the growth of the dermal papilla cells,and methyl thiazolyl tetrazolium (MTT) assay to evaluate the proliferative activity of the dermal papilla cells.Real-time fluorescence-based quantitative PCR was conducted to measure the mRNA expression of cyclooxygenase 2 (COX-2),prostaglandin D2 synthase (PTGDS),prostaglandin E2 (PGE2),prostaglandin F2alpha (PGF2α),G protein-coupled receptor 44 (GPR44),protein kinase B (AKT) and glycogen synthase kinase 3β (GSK3β),and Western blot analysis to determine the protein expression of PTGDS.After 24-hour culture with DMEM containing levocetirizine hydrochloride at different concentrations,enzyme-linked immunosorbent assay (ELISA) was performed to detect the levels of prostaglandin D2 (PGD2) and PGD2R receptor in the culture supernatant of the human dermal papilla cells.Statistical analysis was carried out with SPSS 17.0 software using one-way analysis of variance for the comparison of the above indices among the groups,and least significant difference (LSD)-t test for multiple comparisons.Results Immunofluorescence staining showed that human dermal papilla cells grew well and reached over 90％ confluence in the 100 μg/L levocetirizine hydrochloride group.MTT assay revealed that there were significant differences in the proliferation rate among all the groups (F =42.22,P ＜ 0.05),and the proliferation rate was significantly higher in the 100 μg/L levocetirizine hydrochloride group (115.80％ ± 5.10％) than in the control group (100％,t =28.26,P ＜ 0.05).The mRNA expression(2-△△Ct) of COX-2,PGF2a,PTGDS,GPR44 and AKT all significantly differed among these groups (F =1.97,3.66,2.17,2.66 and 7.32 respectively,all P ＜ 0.05),while no significant difference in the mRNA expression of PGE2 and GSK3β was observed among these groups (F =0.87 and 1.19 respectively,both P ＞ 0.05).The 100 μg/L levocetirizine hydrochloride group showed significantly decreased mRNA expression of COX-2,PTGDS and GPR44 (0.84± 0.08,0.81±0.10 and 0.85 ± 0.09 respectively) compared with the control group (t =1.97,2.17 and 2.66 respectively,all P ＜ 0.05),but significantly increased mRNA expression of PGF2α and AKT (1.96 ± 0.25 and 1.74 ± 0.32 respectively) compared with the control group (t =3.66,7.32 respectively,both P ＜ 0.05).Moreover,the protein expression of PTGDS,PGD2 and PGD2R significantly differed among these groups (all P ＜ 0.05),and was significantly lower in the 100 μg/L levocetirizine hydrochloride group than in the control group (P ＜ 0.05).Conclusion Levocetirizine hydrochloride can promote the in vitro growth of human dermal papilla cells,likely by inhibiting the PGD2-GPR44 pathway and activating the AKT signal pathway.