Immunohistochemical Detection of Bacteria in the Resected Valves was Associated with Stromal Immune Checkpoint Protein Expression that may Contribute to Calcific Aortic Stenosis

Abstract

Aortic stenosis (AS) is a disease characterized by narrowing of the aortic valve (AV) orifice. The purpose of this study was to clarify the significance of bacterial detection and clinicopathological factors, including valve-infiltrating immune cells and disease severity, in relation to AS. After obtaining the written informed consent form from 50 patients with AS, we performed immunohistochemical analysis of lipopolysaccharide (LPS) for gram-negative bacteria and lipoteichoic acid (LTA) for gram-positive bacteria on surgically resected-AVs. Moreover, we evaluated the relationships among the presence of bacteria, immune checkpoint protein PD-L1 expression, and immune cell infiltrations such as CD8-positive T lymphocytes, CD163-positive macrophages, and FOXP3-positive regulatory T cell (Treg) in resected-aortic valves. LPS detection in the resected-aortic valve tissues was significantly associated with stromal PD-L1 expression, valve calcification, and LTA existence in resected samples. We showed that the presence of LPS was significantly related to high PD-L1 expression only in calcified-AVs, not in non-calcified-AVs. Moreover, the high expression of PD-L1 in AS samples without LPS was significantly associated with positive infiltration of CD163-positive macrophages and FOXP3-positive Tregs. Immunohistochemical bacterial detection in resected-aortic valves was associated with PD-L1 accumulation and valve calcification. PD-L1 significantly accumulated only in calcified valves with LPS existence.