Shikonin impairs T lymphocyte proliferation and thymopoiesis while it may increase myeloid-derived suppressor cells...

Shikonin (SHK) has multifaceted physiological functions, including antitumor, anti-inflammatory, and antimicrobial effects. Recently, SHK has been shown to affect immune responses; however, its detailed immune modulatory function in vivo remains unclear. In this study, we demonstrated that SHK not only inhibited T cell proliferation in vitro, but also intensively inhibited thymopoiesis and eliminated CD4/CD8 double-positive thymic progenitor cells in vivo. Treatment of mice with SHK resulted in immune profile alterations, which promoted myelosis in the bone marrow and increased inhibitory immune cells in central immune organs. A decrease in T cells and B cells was observed in the spleen. Using a murine allogenic skin transplantation model, we revealed that short-term treatment of recipients with SHK significantly inhibited skin graft rejection, in which the levels of myeloid-derived suppressor cells (MDSC) were markedly increased. Taken together, our study suggests that SHK can efficiently eliminate proliferating T cells and inhibit thymopoiesis while promoting the generation of MDSC, indicating its potential role in alleviating immune responses in allogeneic organ/cell transplantation.