CYCLOSPORINE-INDUCED PSEUDO-GRAFT-VERSUS-HOST DISEASE IN THE EARLY POST-CYCLOSPORINE PERIOD1

Cyclosporine-induced pseudo-graft-versus-host disease (CIPGVHD) in syngeneic or autologous rat marrow chimeras has clinical and histologic features closely resembling classic graft-versus-host disease in the allogeneic chimera. We describe here the pathology and immunopathology of the usual target tissues in CIPGVHD developing in the first week following CsA (early group). The findings are constrasted to the CIPGVHD developing during the second week post-CsA (later group). Six of 9 rats in the early group had acute-type CIPGVHD in the tongue, skin, liver, intestines, and mainstem bronchi. In general, the lymphocytic infiltrates in these tissues were in intimate contact with injured epithelial cells. The intestines had multiple apoptotic lesions. Class II antigen was prominent in the tongue mucosa, but only patchy expression was evident in 2 skin biopsies. All of the lymphocytes infiltrating the mucosa were CD8+(OX-8)/CD4-(W3/25) T cells (OX-19+). Most of the lymphocytes in the lamina propria expressed CD4 as well as CD8 markers, suggesting coexpression. In the later group, 6 of 7 rats had chronic-type CIPGVHD (1 with acute and chronic) while 1 rat had no GVHD (P = .02, Fisher's exact test compared with the early group). These animals had features characteristic of established chronic GVHD in the skin, tongue, liver, intestines, and salivary glands. Fibrosis of the dermis and lamina propria was prominent in the skin and tongue. Submucosal fibrosis was increased in the small intestine. The salivary glands had an interstitial infiltrate and fibrosis with loss of ducts and glands. Class II antigen was prominent in the epidermis of the tongue and skin of all rats. The number of lymphocytes infiltrating the mucosa of the tongue was considerably smaller than seen in the early group. More than 90% of these cells were T cells, as detected by OX-19, and expressed both CD4 and CD8 markers. While most lamina propria lymphocytes expressed the CD4 antigen, there were significantly fewer CD8+ cells, consistent with increased numbers of CD8-/CD4+ helper-phenotype cells. The observations indicate that immediately post-CsA, the CIPGVHD is primarily acute, with epithelial infiltrates of CD8+/CD4- T cells and lamina propria infiltrates that include double-labeled cells consistent with immature thymocytes. There is a rapid transition to established chronic-type CIPGVHD by the second week. The residual mucosal infiltrate is now dominated by double-labeled T cells or thymocytes while the lamina propria infiltrate has more mature helper-phenotype T cells. Induced RT1.B/D antigen could be important in the pathogenesis of the peripheral tissue manifestations.