Surface expression of IgM is similar in CD27⁻and CD27⁺B cells. Flow cytometric analysis of PBMCs for surface IgM expression. (A) representative histogram of CD27⁻ B cells (CD19⁺ CD20⁺) from a patient without cGVHD (gray area, thin line) and with cGVHD (white area, bold line). Isotype is depicted as think gray line. (B) Representative histogram of CD27⁺ B cells (CD19⁺ CD20⁺) from a patient without cGVHD (gray area, thin line) and with cGVHD (white area, bold line). Gates indicate the frequency of B cells positive for IgM surface expression compared with isotype (thin gray line). (C) Frequency of IgM surface expression on CD27⁻ and CD27⁺ B cells (CD19⁺ CD20⁺) quantified in patients without cGVHD (−cGVHD, n = 5, open circles) and with cGVHD (+cGVHD, n = 7 filled squares). Data are median ± range pooled from 2 independent experiments. *P < .05.