Subclinical myeloproliferative disease and myelofibrosis induced by JAK2^V617F in the absence of STAT5. H&E stain of spleen (A) and liver (B) from a representative pIpC-treated recipient of JAK2^V617F MIGFP-transduced Mx-Cre;Stat5a/b^fl/− BM that engrafted with provirus-positive donor-derived HSCs. In the spleen, a lymphoid follicle (f) and areas of erythroid (e) and myeloid (m) cell infiltration are designated. Magnification is 200×. (C-D) Reticulin stain of BM from a non-pIpC–treated recipient of JAK2^V617F MIGFP-transduced Mx-Cre;Stat5a/b^fl/− BM that developed polycythemia (C) and a pIpC-treated recipient with normal hematocrit (D). Magnification is 600×. All images were obtained from a BH-2 microscope using a Q-Color5 digital camera and QCapture Pro acquisition software (Olympus).