miR-155 expression is up-regulated in the intestinal tract from patients with aGVHD. Histopathologic assessment of human small- and large-bowel samples from patients with aGVHD or from control patients who had a bowel biopsy, but no pathology was observed (controls). In situ hybridization was performed using a digoxigenin-labeled LNA-modified probe complementary to miR-155 or a scrambled LNA control probe. (A) The colon tissue shows marked inflammation with a loss of glands and concomitant erosion. Note that the many inflammatory cells in the lamina propria were positive for miR-155 (dark staining; original magnification ×200). (B) The miR-155 in situ hybridization signal is lost in the same cells in the serial section on using the LNA scramble control probe. (C) A section of ileum shows a normal villous to the left side of the panel, and the loss of the villi in the rest of the section. Note the strong signal in the inflammatory cells in the area of the damaged villi with the miR-155 probe (original magnification ×200). (D) Negative control for panel C, showing loss of the signal with the scrambled probe in the same cells in the serial section. (E-F) The area to the right of the panel C is magnified (original magnification ×400) in panel E (miR-155) and panel F (scrambled probe) to underscore the localization of the signal to mononuclear cells. (G) An earlier stage of GVHD with degenerated/regenerating glands with mononuclear infiltrates, which are primarily located in the lamina propria adjacent to the damaged glands. The miR-155 signal is rare in the damaged epithelial cells but is strong in the adjacent inflammatory cells as shown in higher magnification (×1000) (H) where mononuclear infiltrate into the epithelia, typical of GVHD, is evident. (I-J) Normal colon mucosa negative for miR-155 staining (original magnification ×400).