Negative control shows methylation? - (Jul/03/2007 )

I use SssI-treated DNA for positive control, and DNA extracted from leukocytes of cancer-free subjects as negative control. I tested about 20 samples (human cancer DNA) for MSP, and all of them including negative control showed methylation. I tried BSP for the same gene, and my negative control showed 15 methylated CG sites over 17 CG sites. I'm not sure what I should do next. Could anyone help me please??

Blood leukocyte DNA is NO NEGATVIE CONTROL!!! There are several reports on methylated DNA in blood DNA. If you need a negative control, you can either buy unmethylated DNA or use Whole genome amplification kits to amplify away the methylation patterns.