A significant increase in HLA-DR−CD11b+CD33+ MDSCs, including both CD14+CD66b− monocytic and CD14−CD66b+ granulocytic MDSCs, was reported in the peripheral blood of patients with active SLE, and the frequency of these populations positively correlated with serum Arg1 activity, Th17 responses and lupus severity. Here, ARG1 is linked to systemic lupus erythematosus.