PF4 and rheumatoid arthritis: Intriguingly, a recent study reported CXCL4 expression by activated T cells that limited Th17 differentiation.35 Monocytes have been described to constitutively transcribe and translate CXCL7, which is processed intracellularly into several derivatives known to have signalling and effector functions.36 Together this evidence is supportive of our finding that CXCL4 and CXCL7 is associated with and may be produced directly by macrophages in the synovium during very early RA.