AB0036 Role of programmed death-1 pathway on cd8+ t cells cytotoxicity in primary biliary cholangitis

Background Primary Biliary Cholangitis (PBC) is a chronic progressive autoimmune disease. It has been proven that there was abnormal activation of CD8 +T cells. Previous studies have shown that abnormal expression programmed death-1 (PD-1) and its ligand (PD-L1) in PBC. However, no study was found to confirm the abnormality of PD-1/PD-L1 pathway in CTL in PBC. Objectives To investigate the role of PD-1 and its ligand PD-L1 on CD8+ T cells cytotoxicity in the immunological mechanism of PBC. Methods The expression of PD-1 in peripheral CD8+ T cells of 69 patients diagnosed with PBC as well as 58 health controls (HC) was detected by flow cytometry. Plasma cytokines related to PD-1/PD-L1 pathway were detected by ELISA. The co-localization of PD-1 and CD-8, PD-L1 and CK19 in portal region in liver biopsy was analysed by immunofluorescence assay. Meanwhile, the relative gene expression of PD-1 regulatory pathway in CD8+ T lymphocytes were measured by RT-PCR. And co-culture of PD-1± CD8+ CTL and HiBEC was done in vitro to detect the cytotoxicity, proliferation and cytokine expression of CD8+ CTL and the apoptosis of HiBEC. Results The proportion of peripheral PD-1+ CD8+ T cell decreased in PBC (12.0%±8.8%) than HC (19.9%±12.5%) (p<0.001). The plasma concentration of IL-10, IFN-γ and TGF-β in the PBC group were higher than that in HC (8.29±9.00 pg/ml v.s. 4.43±5.08 pg/ml, p=0.0066; 51.94±52.94 vs 26.71±26.26 pg/ml, p=0.0015; 1302.0±1972.8 pg/ml vs 205.8±298.9 pg/ml, p=0.0018, resp.). Compared with HC (n=19), Tbet gene expression in CD8+ T lymphocyteswas increase in PBC group (n=21) (0.82±0.76 vs 3.03±4.23, p=0.028). Immunofluorescence co-localization revealed that increased PD-1 positive cells in early PBC stage than late one, and less PD-L1 positive cells as well as PD-L1 and CK19 co-localised ones in PBC patients compared to HC. In the CTL and HiBEC co-culture system in vitro, the cytotoxicity of PD-1+ CD8+ T cells was weaker, with less proliferation and tendency of decreased production of IFN-γ and TGF-β compared to PD-1- CD8+ T cells. Meawhile, HiBEC apoptosis was relatively more in PD-1- CD8+ T cells co-cluture group. These effects could be antagonised by anti-PD-1 antibody and enhanced by PD-L1.Abstract AB0036 – Figure 1 Conclusions In PBC, the expression of Tbet is up-regulated in CD8+ T cells, which leads to the down-regulated expression of PD-1 on. Meanwhile, the expression of PD-L1 in HiBEC may be down-regulated. The silenced PD-1/PD-L1 pathway caused more CD8+ T cells proliferation, more related cytokines production and the enhanced CTL cytotoxic effects on HiBEC. PD-1/PD-L1 pathway functions as an important pathway in the immunological mechanism of PBC. References [1] Kaplan MM. N Engl J Med, 1996:335(21):1570–1580. [2] [2] Kita H, et al. J Clin Invest, 2002;109(9):1231–1240. [3] [3] Yang GX, et al. J Immunol, 2011;186(2):1259–1267. [4] [4] Keir ME, et al. Annu Rev Immunol, 2008;26:677–704. [5] [5] Mataki N, et al. Am J Gastroenterol, 2007;102(2):302–312. Acknowledgements This work was supported in part by a grant from Capital Youth Medical Research and Development Fund (No. 2016–4–40111), National Natural Science Foundation (Outstanding Youth Foundation) (No. 81501414) and a grant from The National Key Research and Development Program of ChinaNo. 2016YFA010100). Disclosure of Interest None declared