Immunohistochemical analysis of dendritic cells in skin lesions: correlations with survival time

The response to wounds until healing requires the activity of many cell types coordinate in space and time, so that the types of cells in a wound and their localization may be of help to date lesions with respect to death, which would be useful in forensic pathology. Cells reacting to injury include dendritic cells; the early reaction of these cells to skin wounding has not yet been investigated in humans, which was the aim of this study. Samples of wounded and control skin were taken at autopsy and analyzed by affinity histochemistry. Both epidermal and dermal MHC-II+ cells increased transiently in number within the first hour after wounding, then decreased. In the epidermis the increase affected also CD1a+ cells, i.e. well differentiated Langherhans cells, which however increased less, earlier and for a shorter time period than MHC-II+ cells. Dermal MHC-II+ cells became part of a perivascular mononuclear cell infiltrate visible in the subpapillary dermis by 60 min after wounding, which contained also mast cells. The immediately perivascular MHC-II+ cells were DC-SIGN- and CD11c-, while MHC-II+, DC-SIGN+, CD11c+ dendritic cells were predominantly located at the periphery of infiltrates and some were near the epidermis. Mast cells underwent degranulation, besides increase in number, in the first hours after wounding. The results suggest that skin dendritic cells, including Langerhans cells, participate to the early response to wounding in concert with mast cells, and that subpapillary blood vessels are primary sites of cell infiltration during that response in humans. The results show that the ratio between CD1a positive and MHC-II positive cells in the epidermis, the degranulation index of mast cells and the relative volume of MHC-II positive cells in the dermis can be added to the tools useful to distinguish vital from post mortem lesions and, the first two of them, to estimate the interval between a lesion and death.