Linear regression analysis demonstrating the linear range and sensitivity of qPCR assays used to detect human VAMP2 in pHuVAMP2 using HuVAMP2 primer/probes (A), XMRV in VP62 using BMLV primers/probe (B), MoMLV in pNCS using BMLV primers/probe (C), XMRV in VP62 using XMRV-IN specific primers/probe (D), Balb/c DNA using IAP primers/probe (E) and Balb/c DNA using the BMLV primers/probe (F). Plasmid targets at the indicated copy numbers or Balb/c DNA at the amounts shown were subjected to qPCR in the presence of 1 μg of tRNA as the carrier nucleic acid and the logarithm of these values were plotted against the threshold cycle (CT) value. All data points were derived from triplicate wells and the error bars denote the standard deviation. Data shown are representative of three independent assays except for detection of XMRV in VP62 with XMRVIN specific primers (D) and Balb/c DNA detection with the BMLV primers/probe (F), which were performed once. R2 denotes the Pearson correlation coefficient.