HOXD13 and peeling skin syndrome: The circulating plasma protein levels of sCTLA-4 and sPD-1 in PSS patients (n = 81) were significantly higher than those in controls (n = 83) by ELISA (2.76±0.43 vs. 1.78±0.63 ng/ml, p < 0.0001; 110.31±30.60 vs. 47.98±27.72 pg/ml, p < 0.0001, respectively; Figure 2).