A student is working to compare the methylation pattern of certain interleukins of rheumatoid arthritis patients with healthy persons. So, is it necessary to extract mononuclear cell layer for methylation pattern study of certain interleukin gene? Why not this could be done from whole DNA? Because , in all consulted research articles, analysis of mononuclear cells is suggested for this purpose. But student is facing problem in extracting mononuclear cells. will acknowledge expert views on it.