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.