CD27 and common variable immunodeficiency: We determined the DNA methylation levels of the aforementioned CpG sites in sorted fractions of naïve (CD19+IgD+CD27−), unswitched memory (CD19+IgD+CD27+) and switched memory (CD19+IgD−CD27+) B cells from a total of 23 CVID patients and 17 healthy donors by pyrosequencing of bisulfite-modified DNA.