Early activation of fibroblasts during PDT treatment in leg ulcers.

Abstract This pilot study was aimed to assess the variations of some microscopical parameters in skin ulcers, caused by chronic venous insufficiency of the lower extremities (chronic leg ulcers), in 15 patients refractory to previous conventional treatments during photodynamic therapy (PDT). Samples of control, wounded and PDT treated skin were taken and analyzed by immunohistochemistry. The cellular infiltrate, as well as the thickness of epidermis, vascularization, mast cell and fibroblast numbers, were increased in chronic wounds as compared to healthy skin. After completion of PDT, fibroblasts appeared further increased in number. Mast cells, closely clustered with fibroblasts, also showed an increase in their numbers, degranulation index and expression of basic fibroblast growth factor. The present findings support a primary role of fibroblasts in the wound healing process upon PDT treatment, given their early and intense reaction to injury. Mast cells seem to play an accessory yet important role, on the basis of their number and degranulation index variations and expression of basic FGF. In addition, the clustering of mast cells with fibroblasts around blood vessels suggest that these cells may stimulate angiogenesis and, in parallel, fibroblasts to secrete extracellular matrix during PDT therapy.