A peptide has an amino acid sequence having more than 80% homology with the amino acid sequence listed as SEQ ID NO:4. A nucleic acid molecule has more than 80% homology with one of the nucleic acid sequences listed as SEQ ID NO:1, SEQ ID NO:2 and SEQ ID NO:3. Ligands, anti-ligands, cells vectors relating to the peptide and/or nucleic acid molecule are also used.