The soluble XMRV SU construct was generated by overlapping PCR using pcDNA3.1-VP62 [37] and the previously described pCSI-JSU (for JSRV SU fusion protein) [43] as templates. The first fragment containing XMRV SU was amplified using the following primers: upstream primer (Not I underlined), 59-GCATGCGGCCGCATGGAAAGTCCAGCGTTCTC-39; downstream primer, 59-CCTAGGCCTGTCGACGCCTTTTCA-AACTGGCC-39. The second fragment containing human IgG Fc was generated using the following primers: upstream primer, 59-GGCCAGTTTGAAAAGCTGTCGACAGGCCTAGG -39; downstream primer, 59-TGTATCTTATCATGTCTGGATC-CCC-39. The XMRV SU fused to the human IgG Fc was generated using the two fragments as templates, and the upstream and downstream primer of the first and second fragment, respectively, and then the PCR product was cloned into the pCSI vector.