Quantitative analysis of CD3⁺ T cells, PD-1⁺ T_FH, and Foxp3⁺ cells within PLNs and GCs of ITP and control spleens. The density of CD3⁺ T cells, PD-1⁺ T_FH, and Foxp3⁺ cells in the PLNs and GCs were determined by counting the total number of (A) CD3⁺ T cells, (B) PD-1⁺ cells, and (C) Foxp3⁺ cells and normalizing to the respective area of PLNs or GCs (per 10³ μm² as described in “Quantification of cells in splenic lymphoid nodules”). At least 3 ITP and 3 control spleens were analyzed. Visualization with Zeiss Axio Imager Z1 fluorescence microscope (×200 magnification).