CCL21 is produced by FRCs and CD68⁺ cells. (A) Representative images from nontumoral (upper panels) and CLL (lower panels) lymph node sections stained with anti-CD68 (green), anti-ER-TR7 (blue), or anti-CCL21 (red) antibodies (objective ×63; scale bar represents 12 μm) and merged images in pink (FRC/CCL21) or yellow (CD68/CCL21). Images were acquired using a DMI6000 Leica Spinning Disk microscope with a ×40 1.25NA objective (Leica Microsystems, Wetzlar, Germany) and a Photometrics Coolsnap HQ CCD, driven by Metamorph software (Molecular Devices, Sunnyvale, CA) at the Imaging Facility of Cochin Institute, Paris, France. (B) Masks created from the images in panel A by combining FRC and CCL21 signals or CD68 and CCL21 signals. Pixels are white when both channels are positive and pink when CCL21 is alone. (C) Graph comparing the ratios between colocalized CCL21/CD68 or CCL21/FRC pixels and the total number of CCL21⁺ cells in nontumoral and CLL samples. Measure of the colocalization was obtained by computing the total number of positive pixels. Means were compared in a Student t-test (**P = .0026; n = 8).