EXPERIMENTAL INDUCTION AND ULTRASTRUCTURAL CHARACTERIZATION OF APOPTOSIS IN MURINE ACUTE CUTANEOUS GRAFT-VERSUS-HOST DISEASE

The skin is a primary target organ in acute graft-versus-host disease (GVHD), Recent results suggest that keratinocytes may undergo apoptosi s in acute GVHD, although sequential structural evidence supporting th is concept is lacking, The present study was undertaken to document an d characterize apoptosis, confirmed by endonuclease-mediated DNA fragm entation, in experimental acute GVHD via sequential analysis of ultras tructure. Furthermore, we sought to define whether apoptosis is effect or cell-dependent or independent, and to document cell types responsib le for the scavenging of apoptotic cells, Acute GVHD was produced acro ss minor histocompatibility loci using appropriately matched murine st rains and highly purified preparations of donor CD4(+) and CD8(+) T-ce ll subsets, Transmission electron microscopy was correlated with in si tu labeling of double-stranded DNA breaks by the TUNEL (terminal uridi ne deoxynucleotidyl transferase end ligation) technique, Apoptotic cel ls were observed in all groups receiving T cells, Although most apopto tic cells were found in apposition with effector lymphocytes, a minori ty of apoptotic cells were detected at early time-points prior to lymp hocytic infiltration, Heterogeneous cells, including macrophages, lymp hocytes, Langerhans cells and keratinocytes were involved in scavengin g putative target cells undergoing apoptosis, This study confirms the final pathway of target cell injury in acute GVHD to be apoptosis, In acute GVHD, apoptosis can be induced in the presence or absence of loc al effector cell influx, suggesting at least two mechanisms for the in duction of epidermal target cell injury.