Splenomegaly and reticulin fibrosis in Jak2V617F mice after BM transplantation. (A) Bar graphs indicate an 11-fold increase in spleen weight in Jak2V617F Balb/c compared with Jak2wt Balb/c animals and an approximately 4-fold increase in spleen weight in Jak2V617F C57Bl/6 compared with Jak2wt C57Bl/6 mice. (B) Moderate to marked diffusely increased reticulin fibrosis in BM of Balb/c mice that had received transplants of Jak2V617F 4.5 weeks after transplantation, which was absent in Jak2wt BM (C).