p38 MAPK is activated in low-grade MDS. Bone marrow (BM) biopsies from patients with MDS and control subjects with non-MDS causes of cytopenias were fixed and immunostained with antibody against phosphor-p38 MAPK (A). Histologic examination of 6 representative samples of low- and high-grade MDS and controls revealed more intense staining in low-grade MDS samples. The quantification of p-p38 staining was analyzed by counting the total number of positively stained cells (B) and by measuring intensity of the positively stained cells (C) in 5 hot fields (defined as area of high density of p-p38 staining) and aided by Image Pro Plus software. Error bars indicate SEM. Two-tailed t test shows significantly higher p38 activation per hot field in low-grade MDS samples. Differences in total p38 MAPK protein expression in 5 representative samples from each group were also evaluated in MDS and control bone marrows by immunostaining with an antibody against p38 MAPK (D).