AXIIR is expressed by MM cells and CD138⁺ cells from MM patients. (A) RNA was extracted from CD138⁺ cells from MM patients (nos. 1, 2) and the MM1.S cell line. cDNA was reverse-transcribed and RT-PCR was performed with primers specific to AXIIR and GAPDH. (B) Total protein (20 μg) was extracted from MM cell lines and analyzed for AXIIR expression (AXIIR mouse Ab) by Western blotting. β-actin was used as a loading control. (C) MM1.S cells were incubated with 1 μg/mL bio-AXII alone or in the presence of either 100-fold molar excess unlabeled AXII (unlabAXII) or 100-fold excess annexin V (AXV). A secondary only control with avidin-FITC was included in the experiment. (D) CD138⁺ cells from MM patients (n = 4) were incubated with 1 μg/mL bio-AXII and after extensive washing were incubated with avidin-FITC. Staining was visualized using confocal microscopy. (E) MM1.S cells were incubated with AXIIR Ab (rabbit) at a 1:200 dilution. After extensive washing, the MM1.S cells were then incubated with Alexa Fluor 488. A set of experiments with an IgG control was performed. Staining was visualized using confocal microscopy.