Surface expression of CD74, CD44, and CXCR4 on T cells, monocytes, and B cells. (A) Detection of CD74 with a commercially available FITC-labeled anti-CD74 antibody (n = 8) and PE-labeled milatuzumab (n = 9) on T cells, monocytes, and B cells. For each staining, representative histograms, including an isotype control or blocking experiment, are shown. Competitive blocking experiments were performed by using unlabeled milatuzumab (20-fold concentration). Significant differences were observed between the CD74 expression levels of T cells, monocytes, and B cells (Wilcoxon test), and specificity of the staining was confirmed. (B) Detection of CD74 (n = 10), CD44 (n = 8), and CXCR4 (n = 12) on CD27- naïve and CD27+ memory B cells. These surface molecules showed a distinct expression profile between these B-cell subpopulations (Wilcoxon test). **P ≤ 0.01; ***P ≤ 0.001. BD, BD Biosciences; FITC, fluorescein isothiocyanate; MFI, (geometric) mean fluorescence intensity; PE, phycoerythrin.