Quantification of fibrosis in wild-type and GATA-1^low animals killed at different time points after TPO treatment. Fibers were measured in arbitrary units as described in “Materials and methods” from stained sections similar to those presented in Figure 2, and the data are presented either in absolute values (top) or as mean (SD) percent change, compared with values recorded from untreated controls (bottom). The mean number of fiber intersections (SD/cm) was calculated from values obtained at least on 3 different sections per organ per mouse. At least 3 to 4 mice were analyzed per each experimental point. Values statistically significant from those of untreated animals are indicated: ^* indicates P < .05; §, P < .01.