Immunosuppressive neutrophils with surface expression of lectin-like oxidized low-density lipoprotein receptor-1 (LOX-1) existed at both tumor sites and blood in patients with head and neck squamous cell carcinoma (HNSCC). Their immunosuppressive activities were proved to be induced by endoplasmic reticulum (ER) stress. In addition, ER stress of cancer cells could be “transmissed” to nearby myeloid cells such as dendritic cells and macrophages. Based on these findings, we hypothesized that ER stress of HNSCC could induce LOX-1 expression and immunosuppression of nearby neutrophils.
Conditioned medium (CM) from SCC25 cancer cells with or without treatment of thapsigargin (THG), a common ER stress inducer, was collected. Human neutrophils, isolated from peripheral blood of healthy donors, were then cultured in differently prepared conditioned medium. After 4 hours of culture, LOX-1 expression of neutrophils was evaluated by flow cytometry. In addition, the immunosuppressive effects of these conditioned neutrophils were evaluated by their abilities to inhibit nonspecific T cell proliferation using interleukin-2 (IL-2)/anti-CD3/anti-CD28 system.
Higher percentages of neutrophils expressed LOX-1 after they were cultured in CM from THG-treated SCC 25 cells than in CM from naïve SCC 25 cells. Moreover, conditioned neutrophils by THG-treated SCC 25 cells had more inhibitory effects in T cell proliferation than conditioned neutrophils by naïve SCC25 cells.
ER stress induction of SCC25 could enhance both LOX-1 expression and immunosuppressive activities of neutrophils.
The authors.
Ministry of Science and Technology, Taiwan.
All authors have declared no conflicts of interest.