Circulating platelet–neutrophil complexes represent a subpopulation of activated neutrophils primed for adhesion, phagocytosis and intracellular killing

Platelets play a prominent role in linking the processes of inflammation, haemostasis and thrombosis. Recent studies have shown that platelets form heterotypic aggregates with leucocytes via platelet CD62P and leucocyte beta2 integrins. These interactions have been observed in vitro in blood taken from healthy volunteers and in clinical conditions in which thrombosis and inflammation are prominent. This study investigated the properties of platelet-neutrophil complexes (PNCs) in anticoagulated whole blood. At rest, neutrophils in PNCs exhibit a significantly more activated adhesion molecule profile than free neutrophils with increased CD11b expression and activation (increased binding of the CD11b/CD18 'activation reporter' monoclonal antibody 24) and decreased CD62L expression. In addition, neutrophils in PNCs phagocytosed significantly more Neisseria meningitidis and produced more toxic oxygen metabolites than free neutrophils. Stimulation with the platelet agonist adenosine diphosphate (ADP) led to further increases in CD11b expression and activation, loss of CD62L as well as increased phagocytosis and toxic oxygen metabolite production throughout the whole neutrophil population. When these experiments were repeated with the CD62P blocking antibody G1 the effects were inhibited to a variable extent, dependent upon the parameter under investigation. These results indicate that both soluble and contact-dependent factors contribute to platelet-mediated neutrophil activation. Platelet neutrophil complexes represent a large subpopulation of neutrophils with a more activated adhesion molecule profile, and a greater capacity for phagocytosis and toxic oxygen metabolite production. This study provides further support for a role for PNCs in both health and disease.     

Flow cytometric analysis of defensins in blood and marrow neutrophils

Polymorphonuclear neutrophils (PMN) are vital in host defense against microbial infections. This study provides a flow cytometric method for the quantitative analysis of microbicidal peptides (defensins) in cells of PMN lineage. Rabbit neutrophil peptides, NP-2 and NP-5, were measured in all PMN and in subpopulations of PMN expressing 1-selectin. PMN lineage counts were made on Wright's-stained blood smears and marrow cytospins. Immunoreactivity for NP-2, and NP-5 was detected by using the alkaline phosphatase anti-alkaline phosphatase technique. The results show that marrow PMN express higher levels of NP-2 and NP-5 than blood PMN, p < 0.001 and that these levels are associated with elevated numbers of myeloid precursors. In both blood and marrow, NP-2 occurs in two PMN subpopulations and the mean fluorescence intensity of NP-2 is consistently higher than that of NP-5. Increased levels of defensins are observed in circulating PMN depicting the most 1-selectin p < 0.05. Immunocytochemical results indicate that PMN defensins reside in cytoplasmic granules and are not constitutively expressed on the cell surface. Furthermore, defensins are not detected in monocytes, eosinophils, lymphocytes and erythrocytes. The flow cytometric method described here provides a novel means of quantitating host natural defenses, allows the characterization of PMN subpopulations and has clinical applications.     

Flow cytometry using the monoclonal antibody CD10-Pe/Cy5 is a useful tool to identify follicular lymphoma cells

Follicular lymphoma (FL) is a specific entity defined by characteristic histology, phenotype and molecular rearrangements. Classically, reactivity for CD19, CD10, and strong positivity for the surface light chain immunoglobulin (SIg) are considered to be phenotypic signs typically expressed in FL. In practice, this pattern is difficult to identify since most neoplastic cells analysed by flow cytometry (FC) show weak intensity for CD19-Pe/Cy5 and for SIg and negativity for CD10-FITC. We used triple antigen combinations including two monoclonal antibodies (MoAbs) against CD10 (CD10-FITC and CD10-Pe/Cy5) and a long-distance polymerase chain reaction (PCR) approach to establish the phenotypic pattern of neoplastic cells carrying t(14;18)(q32;q21). Neoplastic cells showed the following immunophenotype: stronger reactivity against CD20 than against CD19, positivity for CD22 and SIg and negativity for CD5, CD11c and CD10-FITC. Characteristically, CD10-Pe/Cy5 was expressed in all the samples with positive bcl-2/JH rearrangements. In FL, there was a high correlation between histologic diagnosis and reactivity against CD10-Pe/Cy5 (96% cases). In diffuse large cell lymphomas (DLCL), CD10-Pe/Cy5 identified positive cases with t(14;18)(q32;q21) chromosomal translocation, whereas Burkitt lymphomas showed all cases reactivity against CD10-Pe/Cy5. In conclusion, CD10-Pe/Cy5 is a useful antibody for identifying neoplastic cells carrying t(14;18)(q32;q21) in FL and DLCL. In combination with other MoAbs, anti-CD10 (HI10a, Cy-Chrome) can be used to identify a characteristic phenotypic profile of FL against other lymphoproliferative disorders.     

hMICL and CD123 in combination with a CD45/CD34/CD117 backbone – a universal marker combination for the detection of minimal residual disease in acute myeloid leukaemia

Real‐time quantitative polymerase chain reaction (qPCR) has been extensively validated for the detection of minimal residual disease (MRD) in acute myeloid leukaemia (AML). Meanwhile, multicolour flow cytometry (MFC) has received less attention because the so‐called leukaemia‐associated immunophenotypes (LAIPs) are generally of lower sensitivity and specificity, and prone to change during therapy. To improve MRD assessment by MFC, we here evaluate the combination of human Myeloid Inhibitory C‐type Lectin (hMICL, also termed C‐type lectin domain family 12, member A, CLEC12A) and CD 123 (also termed interleukin‐3 receptor alpha, IL3RA) in combination with CD34 and CD117 (KIT), as an MRD assay in pre‐clinical and clinical testing in 69 AML patients. Spiking experiments revealed that the assay could detect MRD down to 10^?4 in normal bone marrow with sensitivities equalling those of validated qPCR assays. Moreover, it provided at least one MFC MRD marker in 62/69 patients (90%). High levels of hMICL/CD123 LAIPs at the post‐induction time‐point were a strong prognostic marker for relapse in patients in haematological complete remission (P < 0·001). Finally, in post induction samples, hMICL/CD123 LAIPs were strongly correlated (r = 0·676, P = 0·0008) to applied qPCR targets. We conclude the hMICL/CD123‐based MFC assay is a promising MRD tool in AML.     

Molecular studies reveal that A134T,G156A and G1333A SNPs in the CD177 gene are associated with atypical expression of human neutrophil antigen‐2

Background and Objectives The human neutrophil antigen‐2 (HNA‐2) is expressed on a subpopulation of neutrophils as most subjects present a negative plus a positive HNA‐2 population of neutrophils. The number of neutrophils expressing HNA‐2 is variable and may increase in pregnancy, infections, myeloproliferative disorders and after G‐CSF. This study investigated the presence of polymorphisms in the gene encoding HNA‐2 (CD177) in individuals presenting different patterns of antigen expression and determined the association of single nucleotide polymorphisms (SNPs) with the heterogeneous HNA‐2 expression. Materials and Methods Flow cytometry was employed to analyse the HNA‐2 expression on neutrophils from 135 healthy subjects using two monoclonal antibodies (TAG4, 7D8). Sequencing reactions were performed on subjects whose antigen expression was low (≤ 50%), high (≥ 80%) or atypical (a nonreactive population plus two distinct positive cell populations). Results Five SNPs were detected, two of them (A793C, G1084A) were related to a low expression of HNA‐2 (P = 0·031 and P = 0·004). Atypical antigen expression was observed in 5·9% (8/135) of the individuals, three nonpregnant women and five men. In these cases, the cDNA sequences revealed three SNPs (A134T, G156A and G1333A) strongly related to this atypical HNA‐2 expression (P = 0·004, P = 0·006 and P < 0·0001, respectively). Conclusions Our data show that polymorphisms in the CD177 are associated with variations in the HNA‐2 expression and may be the cause of atypical expressions.     

Rapid quantitative analysis of protein tyrosine residue phosphorylation in defined cell populations in whole blood and bone marrow aspirates

We developed a rapid method for quantification of tyrosine phosphorylation in immunophenotypically defined cell populations in specimens of whole blood and unprocessed bone marrow. Samples were formaldehyde-fixed and cells were permeabilized. Phosphotyrosine residues and surface antigens were simultaneously stained by monoclonal antibodies and visualized by flow cytometry. The accuracy of the method was confirmed by demonstration of an increase of phosphotyrosine levels in pp60 ^v-src transformed fibroblasts. In blood of healthy donors, monocytes and granulocytes showed higher levels of phosphotyrosine than lymphocytes. CD34⁺ peripheral blood stem cells showed slightly increased tyrosine phosphorylation compared to autologous lymphocytes. Significantly elevated levels of phosphotyrosine were demonstrated in leukaemic blasts compared to lymphocytes ( P  = 0.01).     

A flow cytometric assay of CD34-positive cell populations in the bone marrow

Summary CD34⁺ BM cells form a heterogenous population of primitive stem cells and more mature progenitors committed to different lineages of differentiation. By combining CD45 expression with SSC, it is possible to separate immature cells from more diferentiated BM cells, and, by three-colour flow cytometry, analyse the antigens expressed in various subsets of cells. In this paper we show that in the normal BM at least four distinct CD34⁺ cell populations can be identified by their different patterns of CD45 expression and SSC. The most immature CD34⁺ cell population (0.1% of the BM cellularity) lacked all signs of lineage commitment and was CD45RA negative and only weakly CD45 positive. With increasing expression of the CD45 antigens, a second CD34⁺ population (0.2% of the BM cellularity) was formed expressing mainly primitive lymphatic antigens. However. 30% of the cells co-expressed B-cell line antigens and myeloid antigens. Cells committed to the myeloid cell line lost B-cell line antigens, gained CD45 antigen expression and SSC and formed two CD34⁺ cell population (0.2% and 0.1% of the BM cellularity. respectively) differing only with respect to the pattern of myeloid antigen expression and SSC characteristics. Similarly, differentiation along the lymphatic pathway implicated down-regulation of myeloid antigens, loss of the stem cell antigen and immature lymphatic antigens and gain of CD45 expression and mature lymphatic antigens.     

Evaluation of CD4+/CD25+/high/CD127low/- Regulatory T Cells in Rheumatoid Arthritis Patients

Background: Rheumatoid arthritis (RA) is the most common rheumatoid disease of unknown etiology, determined by the articular cartilage destruction and bone loss. The hallmark of RA is the defect in immune tolerance. Regulatory T cells (Treg) play a critical role in the protection of peripheral tolerance. Objective:  To assess the percentage of CD4+/CD25+/high/CD127low/- Treg cells in peripheral blood of RA patients as compared with the healthy individuals. Methods: The number of CD4+/CD25+/high/CD127low/- Treg cells was assessed by multicolor flow cytometry. The clinical disease activity of RA patients was determined by disease activity score 28 (DAS-28). The correlations of DAS-28 and erythrocyte sedimentation rate (ESR) with Treg cells were evaluated. Results: The percentage of CD4+/CD25+/high/CD127low/- Treg cells in peripheral blood of RA patients significantly decreased as compared with the healthy individuals (P= 0.0002). The percentage of CD4+/CD25+/high/CD127low/- Treg cells negatively correlated with DAS-28 and ESR. Conclusion: This study concludes that the defect of Treg cells plays a vital role in the pathogenesis of this disease. Further studies are necessary to determine the role of Treg cells in the clinical course of rheumatoid arthritis.     

Delineation of erythropoiesis in normal and malignant bone marrow using monoclonal antibody AS-E1 directed against transferrin receptors (CD71)

Abstract: We have delineated the erythropoietic compartment in normal and malignant bone marrow (BM) by using the monoclonal antibody (mAb) AS-E1 directed against the transferrin receptor by flow cytometric (FCM) analysis. In normal BM we found a bimodal expression in antigen density with a minor subset (?3%) expressing AS-E1^high and a larger subset (?15%) expressing AS-E1^low. By fluorescence activated cell sorting, morphological examination of smears stained by immunocytochemistry and by BFU–E assays the AS-E1^high fraction was shown to contain cells of erythroid origin (proerythroblasts, basophilic erythroblasts and polychromatic erythroblasts), whereas the AS-E1^low fraction consisted mainly of promyelocytes and myelocytes. In patients with malignant hematological disorders we found a more pronounced heterogeneity in the density and the degree of AS-E1^low expression compared to normal BM, and to further characterize the AS-E1^low cells in patients and to exclude that this broad reactivity interfered with the identification of the AS-E1^high cells, we employed triple-color FCM assays with mAbs directed against the myeloid surface markers CD13 and CD66 in addition to AS-E1. In all patients we found that 80–90% of the AS-E1^low cells co-expressed CD13 and/or CD66 and thus were of myeloid origin. Finally, we evaluated 2 methods for determination of the AS-E1^high subset and found an assay involving forward light scatter and logAS-E1 density to be sufficient. We conclude that AS-E1^high is a valid FCM marker for the normal erythropoiesis.     

Variation in cell yield and proliferative activity of positive selected human CD34+ bone marrow cells along the circadian time scale

Abstract: Variations in cell yield and proliferative activity of human bone marrow (BM) progenitor cells were determined with flow cytometry along the 24-h (circadian) time scale. Equal volumes of BM were aspirated every 5 h, altogether 5 times in 5 healthy men. An average 6-fold higher yield of positive selected CD34+ cells occurred in each subject when BM was aspirated during the daytime and late afternoon, while a lower yield occurred during the night. Using all CD34+ cell yield data normalized to percentage of mean, a significant time–effect was found by ANOVA (p=0.02) and a significant circadian rhythm was detected by the least-squares fit of a 24 h cosine (p=0.02). The 95% confidence limits of the acrophase (time of highest values) were computed to be at midday between 10:24 and 14:48 h. A highly significant correlation (p=0.001) was found between proliferation of positive selected CD34+ cells and the more mature myeloid precursor cells from the same BM aspirates, suggesting a common temporal pattern along the circadian time scale. However, no correlation was demonstrated between proliferation and cell yield of CD34+ selected cells, suggesting that mechanisms other than variation in proliferation may cause the circadian rhythm in stem cell yield. These circadian variations in stem cell yield and proliferation suggest that proper timing within 24 h may potentially be important regarding outcome from progenitor cell harvesting and treatment with haematopoietic growth factors.     

Evaluation of a quantitative determination of CD4 and CD8 molecules as an alternative to CD4+ and CD8+ T lymphocyte counts in Africans

In the developed word, monitoring HIV-infected patients is routinely determined by CD4+ T lymphocyte absolute counts. The reference procedure, flow cytometry, is expensive, requires sophisticated instrumentation and operators with specific training. Due to these limitations, CD4 counting is often unavailable in developing countries. The Capcellia assay is an enzyme-linked immunoassay for quantitative determination of CD4 and CD8 molecules. We evaluated this method in West Africa on blood samples collected from 39 HIV-uninfected and 44 HIV-infected adult subjects. CD4 concentration ranges were determined according to the clinical stages of the disease. We then studied the relationship between the two methods in the HIV-infected patients. The Spearman's rank correlation was 0.61 (95% confidence interval: 0.38-0.76, P < 0.0001). Nevertheless, determination of limits of agreement revealed discrepancies between the two methods, especially for CD4 counts > 0.4 x 10(9)/l, which are discussed. We conclude that the Capcellia assay is a convenient means to determine the immunodepression level where flow cytometric instrumentation is unavailable, and can be complementary to CD4 T lymphocyte enumeration.     

Differential expression of CD3 and CD7 in T-cell malignancies: a quantitative study by flow cytometry

Most T-cell antigens are expressed on normal and neoplastic T lymphocytes and for this reason it is not easy to distinguish between the immunophenotype of normal and malignant T cells. We have addressed this problem by comparing the levels of expression of CD3 and CD7 on T lymphocytes from 18 healthy donors with those of 61 cases of T-cell leukaemia using quantitative flow cytometry with a method that converts fluorescence intensity into number of antigen molecules per cell. Normal T lymphocytes expressed 124 ± 25 CD3 and 20 ± 3 × 10³ CD7 molecules per cell. The mean CD3 values were significantly lower in all types of T-cell leukaemia than in normal T cells ( P < 0.05), with the exception of Sezary syndrome. The lowest CD3 values were found in T-lymphoblastic leukaemia (T-ALL), 30 ± 21 × 10³, and adult T-cell leukaemia/lymphoma (ATLL), 38 ± 31 × 10³, followed by T-prolymphocytic leukaemia (T-PLL), 92 ± 47 × 10³, and granular lymphocyte leukaemia (GLL), 95 ± 21 × 10³. In contrast, the number of CD7 molecules was significantly higher in T-ALL, 35 ± 7 × 10³ ( P < 0.01), and T-PLL, 29 ± 12 × 10³, than the normal controls ( P < 0.01), whereas ATLL and GLL showed a low CD7 expression, 13 ± 3 and 12 ± 3 × 10³, respectively. Our results show that the quantitative analysis of CD3 and CD7 and their combined evaluation may enable a distinction between normal and leukaemic T cells and could facilitate the monitoring of minimal residual disease. This study has also defined the T prolymphocyte as a cell of intermediate maturity between thymic derived and peripheral T lymphocytes.     

Clearance of leukaemic blasts from peripheral blood during standard induction treatment predicts the bone marrow response in acute myeloid leukaemia: a pilot study

Although several parameters are useful for risk stratification of patients with acute myeloid leukaemia (AML), there are no firm criteria for predicting response to induction treatment of individual patients. Daily flow cytometry (FC) analysis, carried out during induction treatment in 30 AML patients, showed that the clearance of blasts from peripheral blood (PBC) correlated closely with response, as assessed by bone marrow FC on day 14, and by morphologic analysis at haematopoietic recovery. Therefore, a major treatment outcome can be predicted very early in AML patients, thus providing an opportunity for tailoring treatment modalities from the outset.     

Detection of hairy cell leukaemia in blood and bone marrow using multidimensional flow cytometry with CD45‐PECy5 and SS gating

CD45 and right angle light scatter (SS) gating are used commonly in clinical flow cytometry to differentiate cells of various lineages ( 10 ). We have used CD45‐PECy5 (Clone J33) since 1998 and have noticed that malignant lymphoid cells such as hairy cells can form distinct populations. Previous studies indicate that hairy cells reside where normal monocytes are usually found in CD45/SS scatter plots ( 14 ). We studied six patients with hairy cell leukaemia (HCL) and found that hairy cells have a higher CD45 mean cell fluorescence than normal lymphocytes and monocytes. Two of the six patients presented with mild unexplained cytopenias, without the usual clinical, morphological and cytochemical findings. In both cases, CD45/SS gating of bone marrow cells showed a small population with strong expression of CD45. The presence of hairy cells was confirmed using a panel of monoclonal antibodies. In one patient with HCL variant, CD45 expression was indistinguishable from that of normal lymphocytes. We conclude that CD45‐PECy5 (Clone J33) is useful for screening peripheral blood and bone marrow and for the detection of HCL without obvious morphological involvement.     

Cell kinetic study of normal human bone marrow hematopoiesis and acute leukemia using 7AAD/PY

We have used the 7AAD/PY method to analyze the cell cycle status of normal human bone marrow hematopoiesis, and found that the cell kinetics differed. There were cells with relatively low levels of RNA in the S-phase (Type I) and a high level in the S-phase (Type 11). T-cells, B-cells, nucleated red cells and CD34+/CD19+ early B-cells in bone marrow were Type I, whereas myelomonocytic subset and CD34+/CD33-dim+ common myeloid cells were Type II. AC133+/CD38-dim cells, which were thought to be lineage-marker negative hematopoietic stem cells, had intermediate amounts of RNA in the S-phase between Type I and II (Type 0). Seventy-four cases of acute leukemia were also analyzed. Most of the T- and B-ALL cases were found to be Type I, most of the ANLL cases were Type II, and there were 10 cases that were Type 0. These findings yielded fundamental information about normal hematopoiesis and acute leukemia.     

Immunohistochemical distinction of haematogones from B lymphoblastic leukaemia/lymphoma or B-cell acute lymphoblastic leukaemia (B-ALL) on bone marrow trephine biopsies: a study on 62 patients

Haematogones are normal, maturing B-cell precursors. They can be confused with neoplastic immature lymphoid cells of B lymphoblastic leukaemia/lymphoma or B-cell acute lymphoblastic leukaemia (B-ALL). Though multi-colour flow-cytometry strategies for distinguishing haematogones from cells of B-ALL are well-described, similar strategies have not been determined for bone marrow trephine biopsies (BMTB). We revisited the morphological and immunohistochemical features (CD20, CD34, TdT and PAX5 expression) in 69 BMTB from 62 patients - 27 with excess haematogones; seven with residual B-ALL after therapy; 18 with no reported excess of haematogones or residual acute leukaemia on BMTB; and 17 diagnostic samples of B-ALL. The distinctive immunophenotypic pattern of BMTB with excess haematogones was of CD34, TdT, CD20 and PAX5 accounting for increasing proportions of cells in the order mentioned, whereas among B-ALL, the immunohistochemical pattern was of CD20, PAX5 and TdT accounting for an equal proportion of cells. Furthermore, among haematogones, the intensity of CD20 expression was extremely heterogeneous as compared to the neoplastic cells in CD20-positive B-ALL. The TdT-positive haematogones were generally small and uniform, while a certain degree of heterogeneity was noticed among neoplastic B-ALL cells. This study provides a practical strategy to distinguish haematogones from B-ALL cells in BMTB.     

Chronic lymphocytic leukaemia CD20 expression is dependent on the genetic subtype: a study of quantitative flow cytometry and fluorescent in-situ hybridization in 510 patients

CD20 is an important therapeutic target in chronic lymphocytic leukaemia (CLL). In order to examine the relationship between CD20 expression and cytogenetic abnormalities, we correlated the fluorescent in-situ hybridization (FISH) genetic subtype of 510 treatment-naïve patients with CD20 expression as measured by quantitative flow cytometry. Patients were classified using the Dohner hierarchial classification. The median numbers of CD20 antigen sites by FISH subtypes were: 17p- ( n  = 26), 9341 per cell; 11q- ( n  = 42), 5886 per cell; +12 ( n  = 93), 23 603 per cell; negative FISH ( n  = 153), 8828 per cell; and 13q- ( n  = 196), 10 781 per cell. Compared to cases with negative FISH, 11q- cases had significantly lower CD20 expression ( P  = 0·001), and +12 cases had significantly higher CD20 expression ( P  < 0·001). The significance of trisomy 12 and high CD20 expression was maintained after multivariate analysis accounting for other disease characteristics. Fifty-nine patients received the combination of rituximab and granulocyte-macrophage colony-stimulating factor as frontline therapy; responses were observed in 13 of 14 (93%) patients with +12, in two of four (50%) patients with 11q-, and in 30 of 41 (73%) patients with negative FISH, 13q- or 17p- CLL. Leukemic CD20 expression differed significantly between FISH subtypes. Patients with trisomy 12 CLL showed strong leukemic cell CD20 expression and had a high rate of response to rituximab-based therapy.     

Circulating CD34+ cells in cord blood and mobilized blood have a different profile of adhesion molecules than bone marrow CD34+ cells

Abstract: The expression of adhesion molecules was studied on CD34+ hematopoietic precursors in cord blood, bone marrow and mobilized blood. The samples were labeled in a double immunofluorescence procedure with a CD34 monoclonal antibody and with antibodies against maturation and differentiation antigens and adhesion molecules. Myeloid precursors formed the majority of the CD34+ cells in all samples. In bone marrow a separate cluster of B-cell precursors with low forward scatter was present. Nearly all CD34+ cells in normal bone marrow expressed VLA-4 and VLA-5, PECAM-1, LFA-3 and HCAM. The majority of the CD34+ cells also had LFA –1 and L-selectin on the surface membrane. A small subset was VLA-2, VLA-3, ICAM-1 or Mac-1 positive. CD34+ cells expressing the vitronectin receptor or the CD11c antigen were rare. Cord blood and mobilized blood CD34+ cells had a lower expression of VLA-2, VLA-3 and VLA-5 and a higher expression of LFA-1, ICAM-1 and L-selectin than bone marrow CD34+ cells. Except for LFA-1, this was not due to the presence of more myeloid precursors in these samples. Low β₁ integrin expression may lead to less adhesion to the extracellular matrix. High expression of L-selectin may facilitate interaction with endothelial cells. Therefore, this phenotype may favour mobilization.     

A longitudinal analysis of paroxysmal nocturnal haemoglobinuria-type cells in patients with bone marrow failure: Results of a prospective multi-centre study in Japan

To determine the prevalence and clinical relevance of glycosylphosphatidylinositol-anchored protein-deficient (GPI[−]) cell populations (paroxysmal nocturnal haemoglobinuria [PNH]-type cells) in patients with acquired aplastic anaemia (AA) or myelodysplastic syndrome (MDS), we prospectively studied peripheral blood samples of 2402 patients (1075 with AA, 900 with MDS, 144 with PNH, and 283 with other anaemia) using a high-sensitivity flow cytometry assay in a nationwide multi-centre observational study. PNH-type cells were detected in 52.6% of AA and 13.7% of MDS patients. None of the 35 patients with refractory anaemia (RA) with ringed sideroblasts or the 86 patients with RA with excess of blasts carried PNH-type cells. Among the 317 patients possessing PNH-type granulocytes, the percentage of PNH-type granulocytes increased by ≥10% in 47 patients (14.8%), remained unchanged in 240 patients (75.7%), and decreased by ≥10% in 30 patients (9.5%) during 3 years of follow-up. PNH-type granulocyte expansion occurred more frequently (27.1%) in the 144 patients who originally carried PNH-type granulocytes ≥1% than in the 173 patients with PNH-type granulocytes <1% (4.6%). This study confirmed that PNH-type cells are undetectable in authentic clonal MDS patients, and the presence of ≥1% PNH-type granulocytes predicts a higher likelihood of PNH-type cell expansion than with <1% PNH-type granulocytes.