Platelet lysate promotes the expansion of T regulatory cells that favours in vitro wound healing by increasing keratinocyte migration and fibroblast production of extracellular matrix components

Background: Platelet lysate (PL) contains a cocktail of growth factors and cytokines that promote tissue repair and regeneration. In vitro studies have shown that PL may affect the reparative function of keratinocytes and fibroblasts, but little is known about the effect of PL on immune cells involved in wound healing. Objectives: To analyse the effects of PL on T cells involved in the wound repair process. Materials and Methods: The effect of PL on T cell proliferation, activation, and cytokine production was measured by ELISA and cytofluorometry and regulatory function based on cytofluorometry and Foxp3 RNA expression. Using an in vitro model of wound healing, we investigated the effect of PL-treated T cells on fibroblast proliferation and production of fibronectin and type-1 collagen as well as keratinocyte migration. Results: PL induced T lymphocyte proliferation and CD69 expression, and promoted a transient upregulation of IFN-γ and TNF-α. However, later on, PL enhanced the number of CD25⁺ T cells releasing TGF-β and expressing Foxp3 RNA, which was accompanied by a suppression in the level of type 1 cytokines. In the in vitro model, supernatants of PL-treated T cells positively affected the reparative capacity of human keratinocytes and induced fibroblast proliferation and production of fibronectin and type-1 collagen. Conclusion: These results indicate that PL temporally regulates T cells during the healing process, enhancing protective cytokines in the early phase, followed by a prominent expansion of TGF-β⁺ T regulatory cells that promote tissue regeneration and dampen the inflammatory response to prevent excessive tissue damage.