Expression of CXCL12 within FL cell niches. (A) Tonsil and FL LN sections were stained with mouse immunoglobulin G1 (IgG1) anti-CXCL12 and mouse IgM anti-CD21L antibodies followed by appropriate secondary antibodies. Dotted lines indicate normal and malignant follicles. Scale bar, 100 µm. (B) CXCL12 was quantified by RT-qPCR in frozen tonsil (n = 5) and FL-LN (n = 12) sections. (C) Sections from invaded FL BM were stained with mouse IgG1 anti-CXCL12 and rabbit anti-CD20 antibodies followed by appropriate secondary antibodies. Nuclei were counterstained with SytoxBlue (white). Dotted lines indicate the bone. Scale bar, 100 µm. Boxes indicate the areas magnified in lower panels, including intratumoral zone (left) and extratumoral zone (right); scale bar, 20 µm. (D) CXCL12 concentration was measured by enzyme-linked immunosorbent assay (ELISA) in BM plasma from HDs (n = 20) and FL patients (n = 20). (E) CXCL12 was quantified by RT-qPCR in whole BM cells (left) and BM-MSCs (right) obtained from HDs (n = 5 and n = 6, respectively) and FL patients (n = 20 and n = 9, respectively). ****P < .0001; ***P < .001; *P < .05.