ROR1 is expressed on a subset of normal B-cell precursors in adult bone marrow. (A-B) Multicolor flow cytometric analysis of BMMCs from healthy donors. Data are representative for results from 3 healthy donors. (A) Analysis of ROR1-expression on CD34⁺CD38⁻lin⁻ hematopoietic progenitor cells. (B) Identification of B-cell precursors at distinct stages of B-cell development, mature B cells and plasma cells based on coexpression of CD19, CD10 and CD45, and analysis of ROR1-expression on the cell surface. Staining with specific polyclonal anti–human ROR1 antibodies (solid black line) versus isotype controls (gray histogram). (C) Activation of primary peripheral B cells of healthy donors by BCR-crosslinking, with PMA/ionomycin and stimulation through CD40. Expression of CD86 (top panel) and ROR1 (bottom panel) before and after activation. (D) ROR1 mRNA expression in normal resting, activated and EBV-transformed B cells analyzed by qPCR. The same B-CLL sample as in Figure 1A (B-CLL #1) was used as a reference and the relative expression of ROR1 compared with GAPDH as housekeeping gene.