An investigation into the mechanisms by which human dermis does not significantly contribute to the rejection of allo-skin grafts.

The dermis is an important element in skin substitutes and in allo- or xeno-skin grafts. However, the reason(s) why dermis does not significantly induce the immune rejection reaction in vivo remain(s) hitherto unknown. To clarify the mechanisms underlying this phenomenon, we undertook the evaluation of: (i) the response of the peripheral blood mononuclear cells (PBM) to isolated allo-dermal cells or to pieces of or to whole allo-dermis, (ii) the migration and homing of the PBM inside allo-dermis or split thickness allo-skin, (iii) the distribution of the ICAM-1 protein within skin, and (iv) the features expressed by the PBM that migrate into allo-skin. The results herein presented show that (1) the isolated allo-dermal cells had the highest and the whole allo-dermis the lowest capacity to initiate the reactive proliferation of the PBM in vitro; (2) in an allo-skin/PBM co-culture model, most of the PBM slowly, yet preferentially, migrated to and homed inside the allo-epidermal compartment, instead of staying in the allo-dermis; (3) under the conditions employed, rather little ICAM-1 could be immunohistochemically detected within the epidermis, conversely, both the dermal cells and the dermal matrix were ICAM-1 positive; and (4) most of the PBM migrating into the allo-skin pieces expressed either the CD18 or the CD19 or the CD8 molecule, yet very few of them exhibited the LFA-1-antigen, and none of them were found to be CD4 positive.2+Therefore, we conclude that because