Romiplostim-induced increase in splenic MKs. (A) H&E-stained paraffin sections of the spleen of romiplostim-treated and control mice. Animals treated with romiplostim (ii,iv) show a clearly visible increase of MKs in the spleen compared with the untreated animals (i,iii). Of note, the number of MKs was already slightly increased in Myh9^−/− mice at baseline (iii). The arrow in panel ii shows a mitosis of a MK (original magnification, ×789). (B) Quantification of MK numbers in the spleen (mean ± SEM of 9-10 animals per column). (C) Spleen weight; mean ± SEM of 9-10 animals per column.