GAPDH and infection: The evidence for this is as follows: (i) XMRV was detected in primary human tissues; (ii) no murine sequences (e.g., GAPDH) could be detected in our materials by PCR; (iii) infection was predominantly restricted to human samples with the QQ RNASEL genotype; (iv) polymorphisms were found in the XMRV clones recovered from different patients consistent with independent acquisition of the virus by these individuals; and (v) viral nucleic acids and antigens could be detected in infected QQ prostate tissue by FISH and IHC, respectively.