Staphylococcal enterotoxin U promotes proinflammatory activity of macrophage via up-regulation of allograft inflammatory factor 1 expression

Staphylococcal enterotoxins (SEs) are a wide array of virulence factors produced by Staphylococcus aureus with potent super-antigenic activity and they were reported to be associated with sepsis-related infections, pneumonia, food poisoning, toxic shock syndrome, and autoimmune diseases. Macrophages play important roles in innate immune responses against bacterial infections. Thus, the present study was conducted to explore the effect of SEU on macrophage activation. Seu gene was cloned from clinical Staphylococcus aureus strain related to food poisoning; then SEU protein was purified by Ni2+ column affinity chromatography. Thereafter, macrophage proliferation was analyzed with a Cell Counting Kit-8 and inflammatory cytokine tumor necrosis factor-alpha (TNF-alpha), interleukin 6 (IL6) secretion was assayed with the corresponding ELISA detection kit. Furthermore, western blot was used to assay inflammation-associated protein allograft inflammatory factor 1 (AIF-1) expression, then the expression of AIF-1 was interfered by RNAi and the effect of SEU on macrophage proliferation and TNF-alpha, IL6 secretion was assessed again. The obtained deoxynucleotide sequence of seu gene (GenBank accession No. MH737695) shared 98.5% similarity with previously identified seu from S. aureus 383F (GenBank accession No. AY205307). SEU protein-enhanced macrophage proliferation and inflammatory cytokine TNF alpha, IL6 secretion. Furthermore, it upregulated AIF-1 expression, thereafter the expression of AIF-1 was interfered by RNAi and the interference abolished the increase of cell proliferation and inflammatory cytokine TNF alpha, IL6 secretion induced by SEU. Current results demonstrated that SEU promoted the proinflammatory activity of macrophage via upregulation of AIF-1expression.