The Transmembrane Envelope Protein of Porcine Endogenous Retroviruses Modulates Cytokine Release and Gene Expression in Human Immune Cells

<jats:p>Porcine endogenous retroviruses (PERVs), their transmembrane envelope protein p15E and peptides corresponding to a highly conserved among all retroviruses domain in p15E, the immunosuppressive (isu) domain, demonstrated immunosuppressive properties. They inhibited in vitro immune reactions, and induced release of IL-6 and IL-10 in human peripheral blood mononuclear cells (PBMCs). We recently showed that p15E of PERV expressed on 293T cells reduced the MHC expression and induced cytokine release in co-incubated human PBMCs. Furthermore, expression of p15E inhibited cytotoxic cells. Here, a new construct with a higher expression of p15E and consequently higher effects on cytokine release was designed and used. Furthermore, a newly developed cytokine assay measuring intracellular cytokine production and a cytokine array to analyze the release of 105 cytokines into the supernatant was developed. The differential gene expression was analyzed by sequencing the RNA of PBMCs incubated with p15E-expressing and wild-type 293T cells. PERV p15E induced an elevated expression of IL-10, IL-6 and 24 other cytokines and modulated the expression of hundreds of genes. Furthermore, coating porcine L23 cells with the synthetic isu peptide of the PERV p15E protein and subsequently co-incubating them with human PBMCs induced IL-10 production, whereas direct addition of the peptide to PBMCs alone did not induce cytokine production. These results indicate that the PERV p15E protein is capable of modulating cytokine release by human PBMCs and inhibiting their cytotoxic activity.</jats:p>