Expression of CD27 by normal and PNH B cells.

Flow cytometry dot-plots show CD27 expression by normal B cells (A) and by normal (CD48⁺) and PNH (CD48⁻) components of CD19⁺ B cells in 5 patients with PNH (B-F). B cells were identified by CD19⁺SSC^low characteristics. The percentage values represent the proportions of PNH and normal B cells expressing CD27. Plot A is from a normal healthy adult donor and shows no GPI⁻ B cells and 30.1% CD27⁺ (memory) B cells. Plots B, C, and D are from 3 patients with PNH, with GPI⁻ B cell clones of 0.19%, 9.64%, and 3.65% and granulocyte PNH clones of 0.9%, 31.3%, and 80.2%, respectively. These show that GPI⁻ B cells are detectable in most patients with PNH regardless of the size of the granulocyte clone and that they have a predominantly naive (CD27⁻) phenotype. Plots D, E, and F are from patients with large PNH granulocyte clones (ie, predominantly GPI⁻ hematopoiesis) and show that the residual normal B cells are predominantly CD27⁺ (memory phenotype). Plot F shows CD27 expression for the normal and PNH fractions of B cells from patient PNH033 who developed hemolytic PNH over 16 years ago. The residual normal B cells are almost all CD27⁺ and furthermore a significant proportion of the PNH B cells (15.5%) have also become CD27⁺, reflecting the long duration of disease in this patient.