Identification of soluble ULBP1 (sULBP1) in AML plasma. (A) ULBP1 ELISA was established (see “Analysis of soluble ULBP1”) and used to detect sULBP1 in C1R-ULBP1 cells (lane 1, culture supernatant gray bar; lane 2, cell lysate, black bar) but not in control C1R-neo cells (lanes 3 and 4). (B) Immunoprecipitation and Western analysis of sULBP1 in cell lysates of C1R-neo control cells (lane 1) C1R-ULBP1 cells (lane 2) and rh ULBP1/Fc (55 kDa; 3 ng, lane 3). Black arrow indicates the full-length ULBP1 molecule of approximately 40 kDa. (C,D) Levels of sULBP and sMICA in plasma from AML patients (n = 43; open symbols) and healthy donors (HD; n = 25; closed symbols), as determined by ELISA. Horizontal bars show the median values. Not significant (P = not significant) or highly significant (P < .001) difference in sULBP1 and sMICA levels in AML versus HD, respectively.