The high expression level of programmed death-1 ligand 2 in oral lichen planus and the possible costimulatory effect on human T cells.

J Oral Pathol Med (2011) 40: 525–532 Background:  Oral lichen planus (OLP) is a T-cell-mediated chronic autoimmune disease whose precise etiology is unknown. The recently identified costimulatory programmed death-1 (PD-1) molecule and its ligands, PD-L1 and PD-L2, have been identified as CD28-B7 family molecules and constitute a regulatory pathway of potential therapeutic use in immune-mediated diseases. Methods:  We examined the expression of two ligands of PD-1 at both the protein and gene level in the focal mucosa and peripheral blood of OLP patients using immunohistochemistry and real-time PCR. Next, we used the PD-L2.Ig fusion protein and observed its effects on T cells, which were co-cultured with IFN-γ-treated keratinocytes (KCs) in the presence of PHA. Results:  We found that the expression of PD-L2 at both the gene and protein level was statistically different in peripheral blood and local lesion tissue of patients with OLP compared to the normal controls. The proliferation ability of T cells and the expression level of IFN-γ in the supernatant of the above co-culture model were significantly augmented (P < 0.05). PD-L2.Ig fusion protein significantly aggravated the apoptosis of T cells, inhibited the proliferation of T cells and decreased the release levels of IL-2 and IFN-γ in the model (P < 0.05). Conclusion:  These data show that the increased expression of PD-L2, as a costimulatory molecule, may have an important modulatory function on the local immune responses of OLP in vivo.