To determine the distribution of SIGIRR in memory CD4 T cells, we investigated the extracellular frequencies of SIGIRR in CD4 T cells from RA patients and healthy controls by flow cytometry and observed a significantly lower proportion of SIGIRR-positive memory CD4 T cells (CD4 + CD45RO + CD45RA −) in RA cohorts (Fig. 2 A, B) (median = 7.6%) than in healthy controls (median = 21.9%). Here, CD4 is linked to rheumatoid arthritis.