Fig 1: Anti-CD137 mAb Results in Disorganization of B Cell Follicle Architecture in the SpleenFour-week-old WT C57BL/6 male mice were inoculated with 103 FFU of CHIKV. At 2 dpi, 400 µg of agonistic anti-CD137 or isotype control mAb was administered by an i.p. route. Spleens were harvested at 6 dpi (A–D), 7 dpi (E and F), and 14 dpi (I–M) for imaging. (A–D) FDCs (green) were stained for CD21/35; IgD+ B cells (red); and T cell zone (turquoise), CCL21. (B and D) Insets of the respective dotted boxes. (E and F) FDCs (green) were stained for CD21/35; IgD+ B cells (red); and CD4+ T cells (snow). White scale bars indicate 50 µm. Yellow arrows indicate IgD+ B cells surrounding FDCs, and white arrows indicate IgD+ B cells at the CCL21+ T cell zone border. (G and H) The number of CD45-CD21/35+CD54+ FDCs in the spleen at 7 and 14 dpi was analyzed by flow cytometry. (G) Representative flow cytometry dot plots of FDCs are shown. (I) B cells (blue) were stained for B220; FDCs (green), CD21/35; and GC B cells (snow), GL7. White scale bars indicate 500 µm or 100 µm (insets). Each symbol represents an individual FDC-containing follicle (J), GC B cell (K), or spleen (L), and bars indicate mean values. Quantification was performed for FDC area per FDC-containing-follicle (J), distance between the closest GC B cells (K), and GC B cells greater than 10 µm from an FDC (L). (M) Left and middle: FDCs (blue) were stained for CD21/35; VCAM-1 (red); merge (white). (M) Right: GC B cells (white) were stained for GL7; VCAM-1+ FDCs (red). White scale bars indicate 200 µm or 50 µm (insets). The images are representative of 3 spleens per group from 2 independent experiments (Mann-Whitney test: ***p < 0.001; ****p < 0.0001; n.s., not significant).