CD363 is a member of the cysteine-rich secretory protein (CRISP) family and is likewise known as CRISP9. PI-16 is a putative serine protease inhibitor and can serve as a binding protein for PSP94 (prostate secretory protein of 94 amino acids) termed PSPBP. Serum levels of PSP94 and PI-16 can reportedly serve as key targets for prostate cancer research. PI-16 is highly expressed by the activated/memory, FoxP3-bright subsets of regulatory T cells. PI-16-positive regulatory T cells expressed uniformly high levels of the chemokine receptors, CCR4 and CCR6, when compared with PI-16-negative T regulatory cells. The results suggest that the CCR4+CCR6+ regulatory T cells are capable of homing to inflammatory sites and regulating effector T cells such as CCR4+CCR6+ Th17-like cells. PI-16 is also expressed by subsets of memory CD4+ and CD8-bright T cells. It is not expressed by B cells or monocytes.