A histological and electron-microscopic study of the cell types involved in rejection of skin allografts in ammocoetes.

The rejection of skin allografts by the larval lamprey, Lampetra reissneri, was studied by light- and electron-microscopy, with particular attention to the cell types involved in the reaction. In all allografts, melanophores were destroyed within 20-60 days (the mean survival time, 36 +/- 12 days). Neither the epidermis nor the underlying collagenous lamella was invaded by host cells until the 60th day. A heavy infiltration of host leucocytes was observed in the allografts in melanophore and adipose layers and in the bundles of muscles. Throughout all stages from 10 to 60 days after the grafting, the cells of the polymorphonuclear leucocyte (PMN) series and eosinophilic granulocytes predominated, but macrophages were not observed at any stages examined. Plasma cells occurred occasionally at later stages (40-60 days) of allograft rejection, but lymphocytes were rarely found at any stages of graft rejection. These observations, combined with the recent finding of the antibody-enhanced phagocytic activity of granulocyte-series cells in the lamprey, indicate that PMNs, but not lymphocytes, function as the major effector cells in allograft rejection in this phylogenetically oldest class of contemporary vertebrates.