Analysis of cell surface immunoglobulin (Ig) M, IgD, IgG, and CD27 expression by normal (CD48⁺) and PNH (CD48⁻) B cells in patients with PNH.

Patient PNH042 (A-D) had a large PNH granulocyte clone (> 95%) and a disease duration of 12 years. The residual normal B cells comprised mainly CD27⁺ memory cells (A). The majority of these were IgM⁺ (B) with only a small proportion class-switched (IgG⁺) cells (C). The PNH B cells had a naive phenotype (CD27⁻) and expressed IgM and IgD. The strength of IgD expression on these naive (CD48⁻) B cells was significantly higher than on the corresponding (CD48⁺) IgD⁺CD27⁺ memory B cells (D). Patient PNH008 (E-H) first developed hemolytic PNH 12 years ago and had no detectable granulocyte or red cell PNH clones at the time of analysis. The large PNH B-cell clone in this patient showed a small proportion of CD27⁺ cells (E) and a small population of class-switched (IgG⁺) PNH B cells (G). The majority of PNH B cells had a naive phenotype, with mainly strong IgD expression (H). The normal B-cell component in this patient comprised naive B cells and both non–class-switched (F, H) and class-switched (G) memory B cells.