PF4 and systemic sclerosis: Circulating CXCL4 was significantly more abundant in SSc [mean ± standard deviation (SD): 99,175 ± 209,215 pg ml−1, range: 0–805,000 pg ml−1, N = 38] compared with HD [2.9 ± 8.2 pg ml−1, range: 0–50 pg ml−1, N = 34, P = 0.0018] and SLE plasma [10,677 ± 35,742 pg ml−1, range: 0–180,000 pg ml−1, N = 34, P = 0.013] (Fig. 1a).