Further, it is possible that the HLA class I-independent killing activity of ACPA+ RA CD8+ T cells might be mediated by an expanded subpopulation of TCRγδ+CD8+ T cells, even though this subpopulation represents a low proportion of the CD8+ T cells in ACPA+ RA ( < 5% of total CD8+ T cells as shown in Fig. 1e). Here, PRTN3 is linked to rheumatoid arthritis.