Supplementary Material for: Native Soluble Carcinoembryonic Antigen Is Not Involved in the Impaired Activity of CD56<sup>dim</sup> Natural Killer Cells in Malignant Pleural Effusion

<b><i>Background:</i></b> Natural killer (NK) cells are lymphocytes of the innate immune system that play a crucial role in tumor immune surveillance. Accumulated data indicated that NK cells in the tumor microenvironment often display a suppressed function. However, the mechanism is not clear. <b><i>Objective:</i></b> In this study, the effects and relative mechanisms of malignant pleural effusion (MPE) from patients with lung cancer on NK cells were researched. <b><i>Methods:</i></b> MPE and peripheral blood (PB) samples were collected from patients with lung cancer. The cytotoxic activity of CD56<sup>dim</sup> NK cells in PB and MPE mononuclear cells was analyzed by flow cytometry. <b><i>Results:</i></b> It was observed that the percentages of total NK cells and a CD56<sup>dim</sup> NK subset in MPE reduced accompanying impaired cytotoxic activity compared with that in paired PB. Cell-free MPE treatment reduced both the proportion and cytotoxic activity of CD56<sup>dim</sup> NK cells in PB from healthy donors. The suppression effects were not based on soluble carcinoembryonic antigen and the inhibitory cytokines interleukin-10 and transforming growth factor-β<sub>1</sub>, but were dependent on the factor with a molecular weight >100 kDa. <b><i>Conclusions:</i></b> These results demonstrated that native soluble carcinoembryonic antigen does not suppress the activity of NK cells, and an unknown factor with a molecular weight >100 kDa plays a critical role in the impairment of CD56<sup>dim</sup> NK cells in MPE, which might lead to tumor progression.