Objective To observe the feasibility of inducible costimulatory(ICOS)target in mice adjuvant-induced arthritis(AIA)models.Methods Twenty BALB/c mice were injected with equal dose of complete Freund's adjuvant(AIA group,n=10)or phosphate buffered saline(control group,n=10)into the right back paws.The second day after injection,ICOS-IRD680 mAb probes were injected in AIA group,while IgG-IRD680 mAb probes were injected in control group through tail vein,respectively.The fluorescent intensity ratio of the right and left paw based on near-infrared fluorescence imaging 24 and 48 h later were compared between groups.The total RNA of mice were extracted for transcriptome sequencing,and differentially expressed genes(DEG)were screened and analyzed.Primary T cells were extracted from the spleen of mice in control group,then magnetic negative T cells were sorted.Activated T cells were stimulated and induced using phoboxylate/ionomycin,the expression level of ICOS protein on the surface of activated T cells were detected,and the safety of probe was also evaluated.Results The expression of ICOS gene in AIA group was significantly up-regulated,and the proportion of T cells was higher than that in control group.ICOS tented to distribute in FoxP3+ regulatory T cells,CD8+T cells and CD4+T cells.The purity of CD3+T cells before and after magnetic negative T cells was 65.31％ and 90.14％,respectively.The proportion of CD4+T cells before and after activated was 7.14％ and 31.20％,respectively,and the mean fluorescent intensity of ICOS protein in activated CD4+T cells(586±25)was significantly higher than that in non-activated CD4+T cells(161±31)(t=25.390,P＜0.001).Twenty-four and 48 h after probe injection,the fluorescent intensity ratio of the right paw/left paw in AIA group was higher than that in control group(t=34.600,P＜0.001;t=23.380,P＜0.001).Compared with control group,no significant pathological change of heart,liver nor kidney tissues of mice in AIA group was detected,while no significant difference of glutamic-pyruvic transaminase,glutamic-oxaloacetic transaminase nor creatinine was found between groups(all P＞0.05).Conclusion ICOS target was safe and feasible for mice AIA models.