Immunohistochemistry was performed as described in a previous study (33 (link)). The paraffin embedded EC tissues and normal tissues from the same donors who met the requirements were collected. First, each tissue was fixed in 4% paraformaldehyde (PBS; Solarbio) for 48 h. Next, ~4 µm consecutive paraffin sections were cut, heated, dewaxed and dehydrated with immunohistochemical method in accordance with the protocol. EDTA solution of 1 mM (pH 8.9–9.1) was used for antigen retrieval and then endogenous peroxidase of tissues was removed. Then, sections were incubated in primary antibody dilution (antibody: PBS 1:500) against TRA2B (cat. no. sc-166829; dil, 1:500; Santa Cruz Biotechnology, Inc.) overnight at 4°C and washed by sterilized PBS at least 3 times. The tissues were then incubated in the presence of peroxidase-conjugated goat anti-rabbit antibody IgG which served as a secondary antibody (mouse, monoclonal, cat. no. A0286; dil, 1:1,000; Beyotime Institute of Biotechnology) at 37°C for 2 h. Then, the sections were stained with diaminobenzidine (ZLI-9031) and counterstained with hematoxylin solution (ZLI-9643) (both from ZSGB-Bio). Ten different fields per group were randomly selected and recorded under a light microscope (Olympus Corp.).