Lymph vessels are increased in intestinal lesions during GVHD in humans. Representative images of lymph vessels in the duodenum of patients without intestinal GVHD (A) and with grade III intestinal GVHD (B). Sections were stained with podoplanin antibody (brown), which is specifically expressed by lymphatic endothelial cells. Destructive mucosal lesions during severe GVHD are associated with lymphatic vascular proliferation. (C-D) Quantification of lymph vessels in duodenum (C) and colon (D) biopsies from patients after allo-SCT without GVHD (GVHD 0) and patients with histological aGVHD grades III-IV. Number of lymph vessels in 10 high-power fields (HPFs) was determined. Bars in ×100 magnification, 100 µm; and in ×200 magnification, 50 µm; n = 12-19 (C); n = 10-11 (D). Error bars indicate mean ± SEM; significance was tested by the Mann-Whitney U test.