This lack of differences in gene expression when comparing CD8+ PD-1+ and CD8+ PD-1- cells within the peripheral blood further highlights that diversity in signalling molecules that may be seen in early RA, however it indicates that not all cell markers and cell subsets that can be detected in early RA are true subpopulations which may be involved in disease pathogenesis. This evidence concerns the gene PDCD1 and rheumatoid arthritis.