ULTRASTRUCTURAL EVIDENCE OF INTESTINAL MUCOSAL MACROPHAGE ACTIVATION AFTER BONE-MARROW TRANSPLANTATION

Previous studies have demonstrated upregulation of intestinal mucosal macrophage CD16 (an Fc receptor for IgG) in bone marrow transplant-(BM T) recipients with graft-versus-host disease (GVHD). We sought to dete rmine whether there was ultrastructural evidence of mucosal macrophage activation in allogeneic BMT recipients and relate appearances to tho se seen in autologous BMT patients and to immunohistological findings. Sigmoid colonic mucosal biopsies from five allogeneic and three autol ogous BMT patients were taken prior to, 30 days after transplant and, in three of the allogeneic patients, 120 days after transplant. These were examined by immunohistochemistry and electron microscopy. Immunoh istological analysis revealed upregulation of lamina propria macrophag e CD16 after transplant in all patients except one autologous BMT reci pient; there were no such changes in total macrophage numbers. Ultrast ructural evidence of lamina propria macrophage activation was prominen t after both allogeneic and autologous BMT. There was an increase in n uclear size accompanied by increased euchromatin and larger nucleoli. in the cytoplasm there were increased numbers of lysosomes, many of wh ich were small and cylindrical, and cytoplasmic flaps were prominent, Phagosomes were less numerous after transplant. These data confirm tha t after BMT intestinal mucosal macrophages become activated. However c hanges in macrophage ultrastructure specific to patients at risk of de veloping clinical GVHD are lacking.