Immunohistochemical investigation of wound healing in response to fractional photothermolysis

Despite growing clinical evidence of ablative fractional photothermolysis (AFP), little is known about the spatiotemporal molecular changes within the targeted compartments. Six subjects received three different single AFP treatments using a scanned $250μm$$CO2$-laser beam. Spatiotemporal changes of skin regeneration were estimated by immunohistochemical investigation (HSP70, HSP72, HSP47, $TGFβ$, procollagen III, CD3, CD20, and CD68) in skin samples $1h$, $3days$, and $14days$ postintervention. The remodeling was uniformly started by regrowth of the epidermal compartment followed by partial to complete replacement of the microscopic ablation zones (MAZ) by newly synthesized condensed procollagen III. From day 3 to 14, the number of macrophages as well as giant cells surrounding the MAZ increased. $TGFβ$ expression was highest $1hto3days$ following AFP. HSP70 and HSP72 expressions were highest $3–14days$ postintervention in the spinocellular layer leading to an upregulation of HSP47. AFP performed by a scanned $CO2$-laser results in an early epidermal remodeling, which is followed by a dermal remodeling leading to a replacement of the MAZ with newly synthesized (pro)-collagen. During this, an inflammatory infiltrate with $CD3+$ and $CD20+$ cells surrounds the MAZ. The count of macrophages and giant cells involved in the replacement of the necrotic zones seems to be crucial for wound healing.