Peptidase inhibitor 16 identifies a unique subset of memory T helper cells with hyperproliferative and proinflammatory properties (IRC8P.477)

T helper (Th) cells play a major role in protecting the body against pathogens. Any imbalance in Th cell subsets could lead to autoimmune and inflammatory diseases. Peptidase inhibitor 16 (PI16), also known as prostate secretory protein of 94 amino acid - binding protein, was recently discovered to be expressed on memory regulatory T cells. This study investigates the expression and function of PI16 on Th cells. In healthy adults, 5-25% of CD4+ Th cells express PI16 with over 90% showing a memory phenotype. PI16+ Th cells have an increased expression of chemokine receptors CCR4 and CCR6 compared with PI16- Th cells. Transwell migration assays showed that more PI16+ Th cells migrated towards the CCR4 and CCR6 ligands (CCL17 and CCL20) compared with PI16- Th cells. After 7 day stimulation using CD3 / CD28 beads, PI16+ Th cells produce more IL-17A and less IFN-g compared with PI16- Th cells. PI16+ Th cells also have a higher expression of ROR-gt compared to PI16- Th cells. Furthermore, in comparison to PI16- Th cells, PI16+ Th cells have an increased proliferative potential and are less responsive to suppression by Treg. The memory phenotype of PI16+ Th cells, the high expression of Th17-like chemokine receptors, increased ROR-gt expression and high production of IL-17A suggest an active role of PI16+ Th cells at the site of infection or inflammation. Further studies are ongoing to understand the functional role of PI16 on Th cells in autoimmune and inflammatory diseases.