PRF1 and rheumatoid arthritis: Analysis of the granzyme-expressing clusters (GZMB+ and GZMK+), demonstrated that GZMB+ clusters express significantly increased levels of the T cell cytotoxicity-related genes GNLY, PRF1, CTSC and CD226 in ACPA+ RA as compared to HCs, while the expression level of these genes is similar in GZMK+ cluster between ACPA+ RA and HC (Fig. 2f, g).