PBMCs were subsequently isolated, followed by flow cytometry to detect CD4+CD25+Foxp3+Treg cells (CD4+ cells were used for sorting) and CD3+CD8−IL-17+Th17 cells (CD3+CD8− cells were used for sorting) (as shown in Additional file 1: Figs. S1, S2), and the Th17/Treg ratio in peripheral blood of elderly patients undergoing lung cancer surgery after different anesthesia was calculated. Here, CD4 is linked to lung cancer.