Objective To explore the efficacy of tacrolimus in treating experimental autoimmune prostatitis (EAP) in rat model and the possible mechanism.Methods SD rats were randomly divided into 4 groups:normal control group,EAP model group,low-dose treatment group,high-dose treatment group.According to administration durations,each group was further divided into two subgroups:2-week group and 4-week group.After successful modeling,rats in low-dose treatment group and high-dose group underwent gastric perfusion with 0.2 mg/(kg·day) and 0.8 mg/(kg·day) tacrolimus respectively for 2 and 4 weeks in a successive way.Concentrations of interleukin (IL)-2 and macrophage inflammatory protein-1α (MIP-1α) in the homogenate of prostatic tissue and serum were tested.Histomorphological changes of prostatic tissue,spleen and thymus gland were observed,with their viscera coefficients being calculated.Results After the intervention of tacrolimus,a decrease in inflammatory cells in prostatic tissue was revealed histomorphologically and glandular cavity wall was repaired to some extent.The concentrations of IL2 were ( 156.80 ± 19.11 ),( 124.56 ± 17.20) and ( 114.46 ± 20.65) ng/L in the serum of M2W,L2W and H2W groups,and MIP-1 α concentrations were ( 164.99 ± 22.25 ),( 112.03 ± 19.90) and ( 104.91 ± 11.91 ) ng/L,respectively.As for the homogenate of prostatic tissue,IL-2 and MIP-1α levels stood at (219.26±23.11),(191.56±19.08),(186.63 ±20.90) ng/L,and (216.46 ±18.50),(196.55 ±17.84),( 194.74 ± 18.14) ng/L respectively.In comparison,in M4W,LAW and H4W groups,concentrations of the two substances were ( 156.23 ± 19.83),( 129.27 ± 17.25),( 134.26 ± 16.11 ) ng/L and (157.93 ±34.55),(159.09 ±29.17),(154.54 ±29.85) ng/L,respectively.In the homogenate of prostatic tissue,data were (217.92 ±23.23),(186.07 ± 11.56),(180.37 ± 18.26) ng/L and (209.66 ±14.65),( 186.17 ± 17.79),( 186.16 ± 18.27) ng/L,respectively.All differences were statistically significant except MIP-1α level in the serum of 4-week subgroup.Conclusion Tacrolimus can reduce the number of inflammatory cells in prostatic tissue in EAP rat model,which may be related to its suppression of the production of IL-2 and activation of T cells. Key words: Tacrolimus; Prostatitis; Interleukin-2