CD27 and rheumatoid arthritis: Therefore, to verify whether the IgD+CD27- B cells in RA patients were actually naïve, single-cell PCR analysis of immunoglobulin heavy chain variable region (IgVH) genes from sorted peripheral blood, IgD+CD27+ and IgD+CD27- RA B cells, was carried out to determine the frequency of somatic mutations in those subsets.