Spatial single-cell analysis of FL tissues. Imaging mass cytometry was performed on tissue section from formalin-fixed paraffin-embedded FL samples (n = 4). (A) Shown is 1 representative image with FOXP3 (green, Tregs), CD4 (pink), CD20 (blue; tumor cells), and CD21 (yellow; follicular dendritic cells) delimiting the follicles and T-cell zone. Scale bar, 100 μm. (B) Scatter plots depicting the median distance of different cell populations to the nearest actTreg, localized either in the T-cell–rich zone or in the intrafollicular area. Statistical differences were calculated using Kruskal-Wallis test and Dunn multiple comparisons (supplemental Table 8). ∗∗∗P < .001 and ∗∗∗∗P < .0001. (C) actTregs can colocalize with CD8 T cells. Shown is a selected area from the T-cell zone of panel A, with FOXP3 (green), TIGIT (pink), and CD8 (blue). Arrow heads point at FOXP3⁺TIGIT⁺ actTregs in proximity to CD8⁺ T cells. (D) actTregs can colocalize with dendritic cells (DCs) and macrophages. Shown is 1 representative area from the image in panel A, with FOXP3 (green), CD11c (pink, DCs), CD68 (blue, macrophages), and CD21 (white). Arrow heads point at Tregs in proximity to DCs, whereas arrows point at Tregs in proximity to macrophages.