Surface marker expression in Tcl-1 tg IRF4^+/+ and Tcl-1 tg IRF4 ΔB/ΔB mice. (A) MHC1, (B) MHC2, (C) CD80, and (D) CD86 surface expression was measured by flow cytometry in healthy C57/BL6 WT littermates (green), Tcl-1 tg IRF4^+/+ (red), and Tcl-1 tg IRF4 ΔB/ΔB (blue) CD19⁺ B cells or CD19⁺ CD5⁺ CLL cells derived from either the spleen or the LNp. All measurements were performed with a proper isotype control to define negative cell populations or to calculate the MFIR. (E) The surface expression of CTLA4 and CD28 was measured in CD8 or CD4⁺ T cells using flow cytometry in cells derived from the spleen or (F) the lymph nodes. MFIR were calculated using an isotype control. Analyzed mouse numbers are depicted on the y-axis. (G) Flow cytometry of PD-L1 MFIR in CLL cells and percent PD-1⁺ cells in either CD4⁺ or CD8⁺ T cells. Genotypes and mouse numbers are depicted on the y-axis. All measurements were isotype controlled and were performed in cells derived from either the spleen or (H) the lymph nodes. MFIR, mean fluorescence intensity ratio.