NK recognition of bone marrow, peripheral blood, and pleural effusion-derived myeloma cell line by purified allogeneic NK cells activated with IL-2. Close circles represent the percentage of specific lysis of distinct myeloma cell targets: (A and D) KMS12BM, (B) KMS21BM, (C) with cross KMS27PB. Close squares indicate the lysis levels of pleural effusion-derived myeloma target cells: (A) KMS12PE, (B) KMS21PE. In panel C and D with X and open diamond the percentage of specific lysis of KMS11PE and KMS26PE, respectively. The ratios used were 25:1, 12:1, 6:1, 3:1 indicated in abscissa as 1, 2, 3, and 4, respectively. Each panel described 1 representative experiment of at least 3 performed. NK cells preferentially killed BM myeloma lines, while PE-derived cells were less NK susceptible.