Optimization of a Model of Full-Thickness Epidermal Burns in the Pig and Immunohistochemical Study of Epidermodermal Junction Regeneration during Burn Healing

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Abstract
In order to obtain a wound model in which healing involved epidermis rebuilding and epidermodermal junction (EDJ) regeneration without involvement of any dermal repair, we optimized a previous model of experimental cutaneous burning with an aluminum bar by testing various conditions of burning associated with different pre- and postburn skin treatments. On the optimized model of full-thickness epidermal burns without any dermal injury, we investigated the kinetics of regneration of 4 EDJ components, from day 2 to day 23 after burning. The epidermal healing was studied by light microscopy and EDJ regeneration by indirect immunofluorescence with one bullous pemphigoid (BP) serum, antisera to fibronectin and to type IV collagen (Coll IV) and the monoclonal antibody 4C 12-8 to laminin. Histologically. neoepidermis. detected from day 2, appeared as a reepidermization tongue which progressed from the burn edges between the overlying necrotic burned epidermis and the underlying uninjured dermis. Epidermis continuity was found to be restored at day 9. Immunohistochemícally, labelling of BP antigen (BPA), Coll IV and laminin extended all along the neo-EDJ, from day 2 to day 23. In contrast, fibronectin labelling was detected only in the proximal and median portions of the neo-EDJ before day 7, then all along the neo-EDJ, from day 7 to day 23. For all the components except Coll IV, the intensity of the labelling beneath the neoepidermis was higher than that of the residual labelling remaining under the necrotic epidermis. Therefore, BPA and laminin regenerated synchronously to neoepidermis whereas fibronectin first regenerated with delay, then synchronously. For Coll IV. since the intensities of labelling beneath the neoepidermis and beneath necrotic epidermis were roughly equal, no conclusion could be drawn. Globally, regneration of EDJ components proceeded sequentially in a first phase, then synchronously with the neoepidermis progression in a second phase. The comparison of these kinetics of EDJ regeneration with those we previously obtained in the pig on a full-thickness cutaneous wound model shows that the chronological order of expression is the same for BPA and fibronectin, but differs for laminin. This indicates that during EDJ regeneration only laminin expression is clearly influenced by the existence or the absence of simultaneous dermal healing.

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