In an experimental model we demonstrated that endothelial cells of all organs are targets of the alloimmune reaction. Here, in 68 digestive biopsies, we found endothelial lesions by immunohistochemistry and ultrastructure in patients with severe acute graft-versus-host disease (GVHD). In contrast, no such endothelial cell alterations were found either in patients without GVHD or in nongrafted controls. In the biopsies with severe GVHD lesions, ultrastructure showed rupture of the capillary basal membrane and extravased red blood cells. These pericapillary hemorrhages were highly correlated with GVHD severity. In a separate cohort of 39 patients who underwent an allogeneic transplantation after a nonmyeloablative conditioning, 8 patients had intestinal biopsies. Three of these latter patients had both severe pathologic lesions of GVHD and similar endothelial lesions, thus, strengthening the concept that endothelial lesions are linked to GVHD severity and not to the intensity of the conditioning regimen.

Oral mucosa lesions are one of the common pathological consequences of acute graft versus host disease (aGVHD), the major complication of allogeneic bone marrow transplantation caused by mature T lymphocytes of donor origin. Oral mucosa damage in aGVHD is characterized by apoptosis induction in the basal keratinocytes, associated with immune effector T-cell infiltration, but its pathogenesis remains unclear because these lesions might result from the patient conditioning therapy that includes radiation and/or chemotherapy. Here, using a murine model of aGVHD that does not involve any conditioning treatment, we show that the earliest detectable oral mucosa lesion is apoptosis of the endothelial cells from chorion capillaries, which precedes basal keratinocyte apoptosis induction. Neither vascular damage nor epithelial-cell death occurred in recipients of allogeneic lymphocytes from CD95 ligand (CD95L)-defective mice. Our findings indicate that oral mucosa lesions in aGVHD are initiated by endothelial-cell death and require CD95L expression by the allogeneic lymphocytes. This early vascular damage may contribute to the induction of further tissue damage in the oral mucosa, through the induction of hypoxia and vascular leakage of immune cells or soluble proapoptotic mediators.

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Tissue processing and analysis require good preservation of both the shape and content of cells. Lowicryl resin is one of the few embedding media that allow good preservation of both tissue architecture and cellular contents. Therefore, different histochemical and immunohistochemical reactions can be applied to semithin sister sections from one biopsy. Further examination of a zone of interest can be carried out under the electron microscope. The hydrophilic property of Lowicryl resins makes possible different histochemical reactions; however, the technique used for paraffin sections must be adapted for each reaction. Antigenic preservation of cells by low temperature embedding allows immunolabeling on either semithin sections or in the zone of interest on ultrathin sections. We have shown the application and adaptation of different histochemical and immunohistochemical reactions on semithin and ultrathin sections from hepatic biopsies that were large, but thin. The variety of techniques that can be used on sister Lowicryl sections of a single biopsy makes this medium useful for extensive pathological studies of precious needle biopsies.