In vitro effects of Staphylococcus aureus enterotoxin C3 on T cell activation, proliferation and cytokine production

The present study aimed to investigate the effects of Staphylococcus aureus enterotoxin C3 (SEC3), including recombinant (r)SEC3 protein and lentivirus‑mediated SEC3, on the activation, proliferation and cytokine production of human T cells. HeLa cells were infected with SEC3 lentiviral vector (LV‑SEC3) and viability was determined using the Cell Counting Kit‑8 (CCK‑8) assay. Subsequently, infected cells or rSEC3 protein were co‑cultured with human peripheral blood mononuclear cells (PBMCs) for 10 days, after which the culture supernatant and T cells were incubated with untreated HeLa cells, which were subjected to a CCK‑8 assay to determine cytotoxicity. In addition, IL‑6 and IFN‑γ expression was detected by chemiluminescence and enzyme‑linked immunospot analyses, respectively. Subpopulations of activated T cells were sorted by flow cytometry. The results demonstrated that, following infection with LV‑SEC3 or negative control lentiviral vector (LV‑NC), >80% of HeLa cells presented green fluorescent protein‑positive signals. All five groups of co‑cultured T cells exhibited proliferation. Co‑culture of PBMCs with rSEC3 protein or LV‑SEC‑infected cells resulted in elevated IL‑6 and IFN‑γ secretion. In addition, rSEC3‑activated and monocultured T cells were predominantly cluster of differentiation (CD)4+ (62.7 and 59.6%, respectively) whereas phytohemagglutinin‑stimulated T cells were predominantly CD8+ (57.8%). Compared with the LV‑NC group, T cells and culture supernatants from the LV‑SEC3 group significantly attenuated proliferation of HeLa cells. These results suggest that rSEC3 protein, and LV‑SEC3‑infected HeLa cells, are able to potently activate T cells, increasing cytokine production and amplify the antitumor immune response.