Figure 2.

Close physical association between Ki67^pos B cells and follicular helper T cells in normal germinal center light zones. (A1) Representative low power image showing polarization of Ki67^pos cells to the dark zones of normal germinal centers. Ki67 (red), PD-1 (white), ICOS (green), DAPI (blue). Scale bar represents 100 μm. The area highlighted by the white rectangle is shown in high power in (A2). (A3) The close association between Ki67^pos FL cells (red) and PD-1^Hi cells (white) is shown in the light zone of another follicle whereas in the dark zone there is less interaction between Ki67^pos cells and PD-1^Hi T cells. The scale bar represents 25 μm. (B1) Using a different four-color panel, the Ki67^pos cells (blue) were confirmed as CD20^pos B cells (red) and the PD-1^Hi cells (white) were confirmed as CD3^pos T cells (green). The scale bar represents 100 μm and the area highlighted by the white rectangle has been magnified in (B2). Images representative of n=13 images from n=4 reactive lymph node (LN) samples. (C) Contingency table showing that Ki67^pos B cells are significantly more likely to be in contact with follicular helper T cells (T_FH) than Ki67^neg B cells in normal germinal center (GC) light zones, as quantified by manual visual assessment. For all samples analyzed together (n=5, Fisher’s exact test P<0.0001).