PLET1 (placenta expressed transcript 1) is a membrane-associated protein that plays crucial roles in tissue repair and cellular differentiation across multiple organ systems. The protein functions as a mediator of cell-cell communication, particularly in wound healing contexts where it promotes epithelial cell proliferation and barrier repair 1. PLET1 is released from alveolar macrophages during lung repair following viral pneumonia, where it induces alveolar epithelial cell proliferation and facilitates epithelial barrier re-sealing 1. In developmental contexts, PLET1 serves as an epigenetically regulated cell surface protein that provides essential differentiation cues for trophoblast stem cells, with its expression levels determining lineage commitment toward either syncytiotrophoblast or giant cell pathways 2. The protein is highly expressed in placental tissues across multiple mammalian species, though human expression is notably reduced due to poor splicing efficiency 3. PLET1 also functions as a marker for bipotent thymic epithelial progenitors capable of generating both cortical and medullary thymic epithelial cells 4. Additionally, PLET1 expression is modulated in inflammatory skin conditions like psoriasis through IL-17A-MAPK signaling pathways 5. The therapeutic potential of PLET1 is highlighted by studies showing that recombinant protein administration can rescue mice from fatal viral lung injury 1.