Data were analyzed with the Bio-Rad CFX Manager Software. MSRV-Env required CD46 Cyt-1 singling and was abolished by the inhibitors of protein kinase C. Finally, both membrane-expressed and secreted MSRV-Env trigger TLR4 signaling, displaying thus a proinflammatory potential, characteristic for this viral protein. These data expand the specter of HHV-6A effects in the modulation of the immune response and support the hypothesis that cross-talks between exogenous and endogenous viruses may contribute to inflammatory diseases and participate in neuroinflammation. Furthermore, they reveal a new function of CD46, known as an inhibitor of match activation and receptor for several pathogens, in transactivation of HERV genes, which may play an important role in the pathogenesis of inflammatory diseases. and was increased in MS patients and correlated to poor TC-E 5006 prognosis (15). The mechanisms responsible for the activation of HERV TC-E 5006 gene expression are poorly comprehended. Infections by some herpesviruses were shown to have transactivating effects on HERV genes. While HSV-1 contamination could activate the FASLG transcription of HERV (16), EBV contamination induces the expression of genes from different HERV, including HERV-W (17, 18). In addition, human herpesvirus (HHV)-6A and HHV-6B were shown to activate the transcription of the Env protein of HERV-K18 (19, 20). Interestingly, both EBV and HHV-6 were also associated to MS pathogenesis (21, 22). However, a more direct link demonstrating the involvement of HHV-6 in MS pathogenesis is still missing. HHV-6A uses CD46 as its access receptor (23). CD46 is usually ubiquitously expressed type I transmembrane glycoprotein explained in the beginning as a match regulatory protein, binding C3b and C4b and acting as a co-factor in their factor I-mediated proteolytic cleavage, preventing thus match deposition on host tissue (24). Another physiological ligand of CD46, the Notch family member Jagged-1, plays a role in Th1 cell responses (25). Extracellular a part of CD46 contains 4 short consensus repeats (SCR) and one Ser-Thr-Pro-rich (STP) domain name close to the membrane and option splicing mechanisms lead to the expression of different isoforms of the CD46 protein, which can be placed into two groups according to their cytoplasmic tail, CD46-Cyt1 or CD46-Cyt2. Human lymphocytes are known as the main targets for HHV-6 contamination, although several cell types from central nervous system (CNS), including astrocytes and oligodendrocytes, have been successfully infected by HHV-6A and, with lower efficiency, by HHV-6B, (26). In addition, several other human pathogens use CD46 as a receptor, including measles computer virus vaccine strain, adenovirus B and D, and (27). This study in the beginning aimed to analyze the potential link between HHV-6A contamination and expression of HERV-W. We have exhibited that both HHV-6A and engagement of its receptor CD46 with several ligands induce MSRV-Env expression. We further recognized the CD46-Cyt1 isoform to be responsible for this effect. Finally, we exhibited the proinflammatory potential of HHV-6A through the induction of MSRV-Env which in turn activates TLR4 receptor. These results provide important information around the cross-talk between HHV-6A binding to its CD46 receptor and the transactivation of HERV-genes leading to inflammation, which may play an important role in the pathogenesis of inflammatory diseases. Materials and Methods Cells Astroglyoblastoma cell collection U87-MG (U87) (ATCC?HTB-14TM) and neuroblastoma SH-SY5Y (ATCC?CRL2266 TM) cells were cultured in Dubelco’s Modified Eagles Medium (DMEM, GibcoTM), complemented with 10% heat inactivated Fetal Calf Serum (FCS), 1% glutamine, 1% penicillin/streptomycin. T-cell collection HSB-2 (ATCC?CLL 120.1TM) was cultured in RPMI-1640 (GibcoTM), 10% of FCS, 1% glutamine, and 1% penicillin/streptomycin. Peripheral blood mononuclear cells (PBMC) from healthy donors were obtained from the Etablissement Fran?ais du Sang of Lyon (France). PBMC were isolated by Ficoll separation from blood samples and cultured in RPMI-1640 medium completed with 10% of FCS, 1% glutamine, and 1% penicillin/streptomycin. Healthy TC-E 5006 donors signed a written Informed Consent Form, documented at the Centre for Blood Transfusion of Geneva, allowing the commercial use of their blood and blood components for medical research after definitive anonymization. Cord blood mononuclear cells (CBMC) were kindly provided by Dr M. TC-E 5006 Ducdodon after density gradient centrifugation of human cord blood and CD34+ cells depletion using immunomagnetic beads (CD34+ MicroBead Kit, Miltenyi Biotec, Bergisch-Gladbach, Germany), as explained previously (28). Umbilical cord blood was obtained from healthy full-term newborns with written parental informed consent according to the guidelines of the medical and ethical committees of Hospices Civils de Lyon and of Agence de Biomdecine, Paris, France. Experiments using cord blood were approved by both committees and were performed in full compliance with French legislation. Computer virus HHV-6A (GS strain) and HHV-6B.