Chronic Granulomatous Disease (CGD) and Complete Myeloperoxidase Deficiency Both Yield Strongly Reduced Dihydrorhodamine 123 Test Signals but Can Be Easily Discerned in Routine Testing for CGD

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Abstract
Background: The flow cytometric dihydrorhodamine 123 (DHR) assay is used as a screening test for chronic granulomatous disease (CGD), but complete myeloperoxidase (MPO) deficiency can also lead to a strongly decreased DHR signal. Our aim was to devise simple laboratory methods to differentiate MPO deficiency (false positive for CGD) and NADPH oxidase abnormalities (true CGD). Methods: We measured NADPH-oxidase and MPO activity in neutrophils from MPO-deficient patients, CGD patients, NADPH-oxidase–transfected K562 cells and cells with inhibited and substituted MPO. Results: Eosinophils from MPO-deficient individuals retain eosinophilic peroxidase and therefore generate a normal DHR signal. The addition of recombinant human MPO enhances the DHR signal when simply added to a suspension of MPO-deficient cells but not when added to NADPH-oxidase–deficient (CGD) cells. Lucigenin-enhanced chemiluminescence (LCL) is increased in neutrophils from MPO-deficient patients, whereas neutrophils from patients with CGD show a decreased response. Conclusions: A false-positive result caused by MPO deficiency can be easily ascertained because, unlike cells from a CGD patient, cells from MPO-deficient patients (a) contain functionally normal eosinophils, (b) show a significant enhancement of the DHR signal following addition of rhMPO, and (c) generate a strong LCL signal.

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