Egg white derivatives induce tumor necrosis factor-α expression in porcine peripheral blood mononuclear cells

Porcine PBMC derived phagocytic activity in peripheral blood polymorphonuclear cells (PMN) induced by egg white derivatives (EWD) treatment was analyzed at the protein and mRNA level. EWD alone failed to induce phagocytic activity of PMN measured by flow cytometry. But PMN phagocytosis was enhanced by culture supernatant from PBMC treated with EWD, human (h)rTNF-α and porcine (p)rIL-1β, respectively. To identify this phagocytic inducing factor, the culture supernatant was partially purified by gel filtration. Only fraction 8 revealed the enhanced PMN phagocytic activity. This fraction also had a high cross-reactivity with anti-prTNF-α polyclonal (p)Ab but not with anti-prIL-1β pAb, as measured by ELISA, indicating that the culture supernatant from PBMC treated with EWD was independent from IL-1β. The enhanced PMN phagocytic activity of fraction 8 was also inhibited by anti-prTNF-α pAb. Both fraction 8 and hrTNF-α produced a single protein band between 16 and 18 kDa upon analysis by sodium-dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and Western blotting using anti-prTNF-α pAb, suggesting that the promoter of PMN phagocytosis is TNF-α, a 16-18 kDa protein produced by EWD-stimulated PBMC. Porcine TNF-α mRNA expression in porcine PBMC analyzed by RT-PCR was also increased by addition of EWD. This study strongly suggests that the immunoenhancing effect of EWD on the phagocytic response of porcine PMN is mediated through TNF-α produced by PBMC stimulated with EWD. In addition, the expression of porcine TNF-α on PBMC is also increased when stimulated with EWD.