Results of XMRV env nested PCR. (A) GAPDH PCR on the DNA of 16 out of the 72 pediatric idiopathic diseases samples. Lanes 1-12 = DNA extracted from whole blood. Lanes 13-16 = DNA extracted from synovial fluid cells. (B) Sensitivity of the XMRV env PCR. Dilution series of 106 to 1 copies of a XMRV plasmid DNA in human genomic DNA. The limit of detection in our assay was 10 copies. (C) Nested PCR with XMRV env primers of the samples shown in A. Lane M, 100 bp marker; lane +, 600 bp PCR positive control from a XMRV env-containing plasmid; Lane-, PCR water control.