PF4 and rheumatoid arthritis: Macrophages in the synovium predominantly secrete the chemokines CXCL4 and CXCL7 in early stage of RA to recruit neutrophils and monocytes (61), but will produce pro-inflammatory mediators TNF-α (63), IL-1β (62), IL-6 (64) and alarmins S100A8/9 (66) throughout active disease.