Ultrastructural findings in acute and chronic graft-vs-hos reaction of the skin.

Two cases of graft-vs-host reaction (GVHR) after allogeneic bone marrow transplantation were studied by transmission electron microscopy. One was observed only in the acute phase and the other, after a mild acute reaction, showed a chronic lichen planus-like pattern. All types of skin damage described in experimental GVHR have been confirmed in both cases. Our findings indicate an involvement of aggressor lymphocytes against keratinocytes as the chief pathogenetic mechanism of the disease, even in its chronic form, although the participation of humoral factors in some phases of the disorder cannot be excluded. The participation of Langerhans cells and macrophages in the reaction could not be demonstrated in these cases.