PDCD1 and Arthritis: SLE patients received three cycles of human IL-2 treatment (1 million IU every other day for 2 weeks, followed by a 2-week break), showing reduced SLEDAI score, less myositis, fever, alopecia, vasculitis, arthritis, oral ulcer, low rate of infection, decreased number of CXCR5+PD-1+CCR7lo Tfh cells, CCR6+CXCR3−CCR4+CCR7lo Th17 cells, and CD4−CD8− αβ T cells at the 12th week, and an elevated proportion of CXCR5+PD-1lo Treg cells and CXCR5+PD-1hi Treg cells and ratios of CXCR5+PD-1lo Treg/Tfh, CXCR5+PD-1hi Treg/Tfh, CXCR5+PD-1lo Treg/Th17, and CXCR5+PD-1hi Treg/Th17 cells (43, 150, 152).