PMN-MDSCs and B cells accumulated in the joints and spleens of CIA mice
We tested the frequencies of PMN-MDSCs and M-MDSCs in different tissues of CIA mice and found that the PMN-MDSC ratio in CD11b+ cells increased significantly in the joints and spleens of CIA mice compared with the control group (DBA/1J mice) (Fig. 1A, 1 B), whereas M-MDSC frequencies were not significantly different between the joints and spleens (Fig. S1A, S1B). PMN-MDSCs accounted for a higher proportion of CD11b+ cells than M-MDSCs in the two tissues mentioned above, particularly in the joints. Furthermore, the frequencies of PMN-MDSCs from the joints of CIA mice correlated positively with the clinical arthritis scores of joints (Fig. 1C), indicating that PMN-MDSCs play an important role in arthritis severity. We tested the IgG concentration in plasma and found that it increased significantly in CIA mice (Fig. 1D). In addition, we examined the B cell subsets using flow cytometry, finding that the frequencies and absolute number of Ki67 and TNF-𝛂 in B cells increased significantly both in the joints (Fig. 1E) and spleens (Fig. 1F), which indicted that B cells abnormal activation also played an important role in the pathogenesis in CIA.