Recruitment of mononuclear cells by endothelial cell binding into wounded skin is a selective, time-dependent process...

Wound healing involves a complex series of interactions between cells in the dermis and epidermis, and important relationships exist between keratinocytes and resident dermal cells. Monocytes and lymphocytes secrete cytokines that are capable of stimulating dermal repair and influencing keratinocyte and fibroblast migration and proliferation, although the mechanism by which mononuclear cells are recruited into the wound is unknown. We have tested the hypothesis that in wounded skin specialized endothelial cells are induced to mediate peripheral blood mononuclear cell (PBMC) emigration from the vasculature into the dermis. For this purpose, partial-thickness wounds made with a keratome on the backs of domestic pigs were excised 0 to 9, 12, 15, and 21 d after wounding. The biopsies were then tested for the capacity to adhere selectively to PBMC. The results indicated that PBMC overlaid onto sections of wounds from day 4 to 15 adhered selectively to dermal endothelium, with two distinct peaks of adherence observed on day 7 and day 12. In contrast, PBMC did not adhere to the tissue sections when overlaid onto frozen sections of normal skin or 0-, 1-, 2-, 3-, and 21-d-old wounded skin. Additional studies on the binding properties of PBMC subsets revealed that monocytes adhered maximally at day 7, whereas T cells adhered optimally at day 12 post-wounding. Furthermore, the adhesion process was energy and magnesium dependent but not calcium dependent and involved surface protein and carbohydrate moieties on PBMC surface. Pre-treatment of PBMC with monoclonal antibodies against the LFA-1 adhesive receptors inhibited the binding by greater than 80%, suggesting that LFA-1 adhesive receptors play an important role in the binding process. These studies provide evidence that the recruitment of monocytes and lymphocytes into wounds is an active, dynamic, and regulated process mediated at least in part by specific adhesive interactions between mononuclear leukocytes and dermal endothelial cells.