Immunophenotypic assessment of PNH clones in major and minor cell lineages in the peripheral blood of patients with paroxysmal nocturnal hemoglobinuria

Background

Flow cytometric immunophenotyping is essential for the diagnosis of paroxysmal nocturnal hemoglobinuria (PNH). Most cases have easy to interpret flow cytometry profiles with red cells, neutrophils and monocytes showing complete deficiency of glycophosphatidylinositol (GPI) linked antigen expression. Some cases are more challenging to interpret due to the presence of multiple populations of PNH cells and variable levels of GPI antigen expression.

Methods

We studied 46 known PNH patients, many with complex immunophenotypic profiles using a novel, single tube, multi-parameter 7-color immunophenotyping assay that allowed simultaneous detection and assessment of PNH clones within multiple lineages of peripheral blood leucocytes. Red cell PNH clones were also assessed in total and immature (CD71+) components by CD59 expression.

Results

For individual patients, total PNH clones in each cell lineage were highly correlated. Monocytes, eosinophils and basophils showed the highest proportions of PNH cells. Red cell PNH clones were typically smaller than monocyte and neutrophil PNH clones. In most cases, PNH clones were detectable in minor leucocyte populations where multiple populations of PNH cells were present, variability in the proportions of type II and type III cells was seen across different cell lineages, even though total PNH clones remained similar.

Conclusions

This study shows that PNH patients with multiple PNH clones do not always display the same abnormality across all cell lineages routinely tested. There is no simple explanation for this but is likely due to a combination of complex molecular, genetic and biochemical dysfunction in different blood cell types.