CD1d cytoplasmic tail structural requirements for CD1d-induced cell death. (A) The CD1d-negative KMS11 myeloma cell line was transduced with empty retroviral vector only, full-length of human CD1d cDNA, full-length CD1d cDNA in which the Y residue of the YXXZ motif was mutated to A (CD1dY > A) or cDNA encoding CD1d with truncated cytoplasmic tail (CD1dTr). CD1d expression by flow cytometry (top) and immunoblotting (bottom) is shown. (B) Role of cytoplasmic tail in myeloma cell aggregation. Aggregation of KMS11-CD1d, KMS11-CD1DY > A, and KMS11-CD1dTr cells at 12 hours after treatment with anti-CD1d or IgG control. (C) Cell death of KMS11-vector only, KMS11-CD1d, KMS11-CD1DY > A, and KMS11-CD1dTr cells as detected by annexin⁺ at 24 hours after treatment with anti-CD1d: P > .05 for KMS11-CD1d vs KMS11-CD1dY > A at 24 and 36 hours; P < .01 for KMS11-CD1d vs KMS11-CD1dTr at 24 and 36 hours; n = 5. (D) Mitochondrial membrane potential loss shown as DiOC3− cells in KMS11-vector only, KMS11-CD1d, KMS11-CD1dY > A, and KMS11-CD1dTr cells after treatment with anti-CD1d. Data shown represent mean plus or minus SEM of 3 independent experiments.