SELL and arthritic joint disease: According to the expression levels of CD44 and CD62L (Supplementary Figure 9A, available on the Arthritis & Rheumatology website at http://onlinelibrary.wiley.com/doi/10.1002/art.41920/abstract), cluster 2 was mainly memory T cells, clusters 1 and 3 were identified as naive T cells, and cluster 4 was identified as effector T cells.