Over-Expression of Immunosuppressive Molecules, PD-L1 and PD-L2, in Ulcerative Colitis Patients

BACKGROUND: Ulcerative colitis (UC) and Crohn's disease (CD) are the two forms of inflammatory bowel disease (IBD). Adaptive immune responses involving helper T cells play an important role in developing IBDs. Programmed death (PD)-1 and its ligands namely PD-L1 and PD-L2 are negative costimulatory molecules that control T cell motility and formation of an immune synapse between T cells and antigen-presenting cells (APCs). OBJECTIVE: To investigate the role of PD-L1 and PD-L2 in patients with UC to clarify the mechanism of IBD development. METHODS: Biopsy specimens were obtained from 50 UC patients and 45 sex- and age-matched control subjects. Total RNA was extracted from all samples and applied for cDNA synthesis. Relative expression of PD-L1 and PD-L2 mRNA was determined using Taqman qRT-PCR. RESULTS: Relative gene expression levels of both PD-L1 and PD-L2 were higher in UC patients than the control groups (p<0.05 and p<0.01, respectively). Furthermore, both PD-L1 and PD-L2 expressions were positively correlated in all study subjects (r=0.339, p<0.001). However, among the groups with disease severity, the relative gene expression levels of PD-L1 and PD-L2 showed no significant difference. CONCLUSIONS: During IBD, the occurrence of PD-L1 and PD-L2 up-regulation may modulate the chronic inflammation of colonic mucosa.