Spleen analysis of untreated and treated JAK2+/V617F mice. (A) Comparison of splenic weight measurement of untreated healthy JAK2+/+ mice (n = 13), untreated JAK2+/V617F mice (n = 14), and anti–IL-6– (n = 9) and IgG-treated JAK2+/V617F mice (n = 10), respectively. Data are shown as mean ± standard error of the mean. JAK2+/+ vs JAK2+/V617F data are our laboratory’s internal control and are also partly reported in a manuscript by Müller et al.24 (B) Representative images of the isolated spleens of untreated healthy JAK2+/+, untreated JAK2+/V617F, and anti–IL-6 Ab– and IgG-treated JAK2+/V617F mice are shown (scale bar, 1 cm). (C) Representative images of histopathologic spleen sections are shown (scale bar, 500 μm). Isolated spleens of untreated JAK2+/+ and JAK2+/V617F mice as well as anti–IL-6– and IgG-treated JAK2+/V617F mice were stained with hematoxylin and eosin. DM6000 B Microscope (Leica Microsystems, Wetzlar, Germany) and LAS (version 3.8) software (Leica Microsystems) were used for micrographs at room temperature. ****P < .0001 by nonparametric, 2-tailed Mann-Whitney test.