Immunohistochemical analyses of spleen, liver, and bone tissues after the establishment of disease from MEC-1 cells with WT or mutant BTK. Representative macroscopic images of spleens from each group are provided in the top row. Spleen, liver, and bone tissues were collected at the time of euthanasia. B-cell marker expression (CD19 and CD20) and proliferation marker expression (Ki-67) are shown for the spleen, liver, and bone marrow from mice with no disease and from BTK^WT, BTK^C481S, and BTK^C481R mice.