Method for detecting the expression of an envelope protein of a human endogenous retrovirus and uses of a gene coding for said protein

A method for detecting whether an interaction occurs between a polypeptide of a producer cell and a neutral amino acid transporter cell surface receptor of an indicator cell ex vivo or in vitro, wherein the polypeptide has a sequence which consists of SEQ ID NO:1, said method comprising:

• contacting said indicator cell with said producer cell;
• observing formation of syncytia between said producer cell and said indicator cell or non-formation of syncytia between said producer cell and said indicator cell;
• and
• correlating said formation of syncytia with occurrence of an interaction between the polypeptide of the producer cell and the neutral amino acid transporter cell surface receptor of said indicator cell or correlating said non-formation of syncytia with a lack of an interaction between the polypeptide of the producer cell and the neutral amino acid transporter cell surface receptor of said indicator cell.