RESUMEN
Congenital neutropenia with autosomal recessive inheritance was first described by the Swedish paediatrician Rolf Kostmann who coined the term 'infantile genetic agranulocytosis'. The condition is now commonly referred to as Kostmann disease. These patients display a maturation arrest of the myelopoiesis in the bone marrow and reduced neutrophil numbers and suffer from recurrent, often life-threatening infections. The molecular mechanism underlying congenital neutropenia has been intensively investigated, and mutations in genes that impinge on programmed cell death have been identified. The present review provides an overview of these studies.
Asunto(s)
Neutropenia , Síndromes Congénitos de Insuficiencia de la Médula Ósea , Humanos , Mutación , Neutropenia/congénito , Neutropenia/genética , SíndromeRESUMEN
OBJECTIVES: The distinction between bacterial and viral causes of acute infections is a major clinical challenge. In this report we investigate the diagnostic performance in this regard of nine candidate biomarkers together with HNL (Human Neutrophil Lipocalin). METHODS: Blood was obtained from patients with symptoms of infectious (nâ¯=â¯581). HNL was measured in whole blood (B-HNL) after pre-activation with the neutrophil activator fMLP or in plasma (P-HNL). Azurocidin also known as heparin-binding protein (HBP), Calprotectin, PMN-CD64, CRP (C-reactive protein), IP-10 (Interferon γ-induced Protein 10â¯kDa), PCT (Procalcitonin), TK1 (Thymidine kinase 1), TRAIL (TNF-related apoptosis-inducing ligand) were measured in plasma/serum. Area under the ROC (receiver operating characteristics) curve (AuROC) was used for the evaluation of the clinical performance of the biomarkers. RESULTS: Side-by-side comparisons of the ten biomarkers showed large difference in the AuROC with B-HNL being the superior biomarker (0.91, 95% CI 0.86-0.95) and with the other nine biomarkers varying from AuROC of 0.63-0.79. The combination of B-HNL with IP-10 and/or TRAIL increased the diagnostic performance further to AuROCs of 0.94-0.97. The AuROCs of the combination of CRP with IP-10 and/or TRAIL were significantly lower than combinations with B-HNL 0.87 (95% CI 0.83-0.91). CONCLUSION: The diagnostic performance of whole blood activated HNL was superior in the distinction between bacterial or viral infections. The addition of IP-10 and/or TRAIL to the diagnostic algorithm increased the performance of B-HNL further. The rapid analysis of HNL, reflecting bacterial infections, together with biomarkers reflecting viral infections may be the ideal combination of diagnostic biomarkers of acute infections.
Asunto(s)
Infecciones Bacterianas/diagnóstico , Análisis Químico de la Sangre , Lipocalinas/sangre , Neutrófilos/metabolismo , Virosis/diagnóstico , Adolescente , Adulto , Anciano , Anciano de 80 o más Años , Infecciones Bacterianas/sangre , Infecciones Bacterianas/microbiología , Biomarcadores/sangre , Quimiocina CXCL10/sangre , Diagnóstico Diferencial , Femenino , Humanos , Masculino , Persona de Mediana Edad , Valor Predictivo de las Pruebas , Reproducibilidad de los Resultados , Ligando Inductor de Apoptosis Relacionado con TNF/sangre , Virosis/sangre , Virosis/virología , Adulto JovenRESUMEN
The distinction between causes of acute infections is a major clinical challenge. Current biomarkers, however, are not sufficiently accurate. Human neutrophil lipocalin (HNL) concentrations in serum or whole blood activated by formyl-methionine-leucine-phenylalanine (fMLP) were shown to distinguish acute infections of bacterial or viral cause with high accuracy. The aim was therefore to compare the clinical performance of HNL with currently used biomarkers. Seven hundred twenty-five subjects (144 healthy controls and 581 patients with signs and symptoms of acute infections) were included in the study. C-reactive protein (CRP), the expression of CD64 on neutrophils, procalcitonin (PCT), and blood neutrophil counts were measured by established techniques, and HNL concentrations were measured in whole-blood samples after activation with fMLP. All tested biomarkers were elevated in bacterial as opposed to viral infections (P < 0.001). CRP, PCT, and CD64 expression in neutrophils was elevated in viral infections compared to healthy controls (P < 0.001). In the distinction between healthy controls and patients with bacterial infections, the areas under the receiver operating characteristic (ROC) curves were >0.85 for all biomarkers, whereas for the distinction between bacterial and viral infections, only HNL concentration in fMLP-activated whole blood showed an area under the ROC curve (AUROC) of >0.90 and superior clinical performance. The clinical performance of HNL in fMLP-activated whole blood was superior to current biomarkers and similar to previous results of HNL in serum. The procedure can be adopted for point-of-care testing with response times of <15 min.
Asunto(s)
Infecciones Bacterianas/diagnóstico , Biomarcadores/sangre , Lipocalinas/sangre , Proteínas Proto-Oncogénicas/sangre , Virosis/diagnóstico , Enfermedad Aguda , Proteínas de Fase Aguda/análisis , Adulto , Anciano , Infecciones Bacterianas/inmunología , Proteína C-Reactiva/análisis , Diagnóstico Diferencial , Femenino , Humanos , Lipocalina 2 , Masculino , Persona de Mediana Edad , Pruebas en el Punto de Atención , Curva ROC , Receptores de IgG/análisis , Sensibilidad y Especificidad , Virosis/inmunologíaRESUMEN
UNLABELLED: The distinction between causes of acute infections is a major clinical challenge. Current biomarkers, however, are not sufficiently accurate. Human neutrophil lipocalin (HNL) in serum distinguishes acute infections with high accuracy, but in the emergency setting the assay time should be <15-20min, which excludes the use of serum samples. The aim was therefore to develop a novel rapid assay principle and test its clinical performance. METHODS: Serum and neutrophils obtained from 84 infected and 20 healthy subjects were used in the experimental study. 725 subjects (144 healthy controls and 581 patients with signs and symptoms of acute infections) were included in the clinical study. HNL was measured in EDTA-plasma by ELISA or in heparinized whole blood after fMLP activation by a prototype point-of-care assay. RESULTS: Increased release of HNL from neutrophils after activation with fMLP was seen already after 5 min incubation. The release of HNL from purified neutrophils after 15 min incubation with fMLP was significantly correlated to the HNL concentrations in serum obtained from the same patient (r = 0.74, p < 0.001). In the distinction between healthy controls and patients with bacterial infections, the areas under the ROC-curves were 0.95 (95% CI 0.91-0.97) and 0.88 (95% CI 0.84-0.91) for HNL in fMLP-activated whole blood and EDTA-plasma, respectively, (p < 0.001) and in the distinction between bacterial and viral infections 0.91 (95% CI 0.86-0.95) and 0.76 (95% CI 0.70-0.81), respectively (p < 0.001). CONCLUSION: The clinical performance of HNL in fMLP-activated whole blood was superior to HNL in EDTA-plasma and similar to HNL in serum. The procedure can be adopted for point-of-care testing with response times of <15 min.
Asunto(s)
Infecciones Bacterianas/sangre , Infecciones Bacterianas/diagnóstico , Lipocalinas/sangre , Neutrófilos/metabolismo , Virosis/sangre , Virosis/diagnóstico , Enfermedad Aguda , Adulto , Anciano , Biomarcadores/sangre , Femenino , Humanos , Masculino , Persona de Mediana Edad , N-Formilmetionina Leucil-Fenilalanina/farmacología , Neutrófilos/efectos de los fármacos , Neutrófilos/inmunología , Reproducibilidad de los Resultados , Sensibilidad y EspecificidadRESUMEN
OBJECTIVE: To evaluate the Trillium Diagnostics Leuko64(™) assay on Abbott Celldyn Sapphire haematology analyser compared to two flow cytometry protocols on Beckman Coulter EPICS MCL flow cytometer. MATERIALS AND METHODS: CD64 expression on neutrophils was determined by two flow cytometry protocols and by a commercial assay on an automatic haematology analyser. The inclusion of study subjects was based on elevated procalcitonin (PCT) values, identifying patients where a systemic infection was suspected. Healthy blood donors were used as a reference group. RESULTS: Statistically significant correlations between the Trillium Diagnostics Leuko64(™) assay and the flow cytometry methods were found when measuring neutrophil CD64 expression. CONCLUSIONS: The good correlation between a reference method and an automated haematology analyser method for CD64 expression on neutrophils supports introduction of the latter assay for routine use as an independent biomarker of bacterial infection and inflammation.
Asunto(s)
Citometría de Flujo/instrumentación , Citometría de Flujo/métodos , Pruebas Hematológicas/instrumentación , Neutrófilos/metabolismo , Juego de Reactivos para Diagnóstico , Receptores de IgG/metabolismo , Intervalos de Confianza , Femenino , Humanos , Masculino , Persona de Mediana Edad , Estándares de ReferenciaRESUMEN
MOTIVATION: Understanding the substrate specificity of human immunodeficiency virus (HIV)-1 protease is important when designing effective HIV-1 protease inhibitors. Furthermore, characterizing and predicting the cleavage profile of HIV-1 protease is essential to generate and test hypotheses of how HIV-1 affects proteins of the human host. Currently available tools for predicting cleavage by HIV-1 protease can be improved. RESULTS: The linear support vector machine with orthogonal encoding is shown to be the best predictor for HIV-1 protease cleavage. It is considerably better than current publicly available predictor services. It is also found that schemes using physicochemical properties do not improve over the standard orthogonal encoding scheme. Some issues with the currently available data are discussed. AVAILABILITY AND IMPLEMENTATION: The datasets used, which are the most important part, are available at the UCI Machine Learning Repository. The tools used are all standard and easily available. CONTACT: thorsteinn.rognvaldsson@hh.se.
Asunto(s)
Algoritmos , Proteasa del VIH/química , Proteasa del VIH/metabolismo , Oligopéptidos/metabolismo , Inteligencia Artificial , Humanos , Máquina de Vectores de SoporteAsunto(s)
Inhibidores de Hidroximetilglutaril-CoA Reductasas/efectos adversos , Transportadores de Anión Orgánico/genética , Técnicas de Genotipaje , Humanos , Inhibidores de Hidroximetilglutaril-CoA Reductasas/farmacocinética , Inhibidores de Hidroximetilglutaril-CoA Reductasas/uso terapéutico , Transportador 1 de Anión Orgánico Específico del Hígado , Enfermedades Musculares/inducido químicamente , Enfermedades Musculares/genética , Medición de Riesgo , Factores de Riesgo , Simvastatina/efectos adversos , Simvastatina/farmacocinética , Simvastatina/uso terapéuticoRESUMEN
OBJECTIVES: To investigate the cause of apparent hyperkalemia in leukemic heparin plasma. DESIGN AND METHODS: Lithium heparin plasma and serum samples from a patient with chronic lymphocytic leukemia (CLL) with hyperleukocytosis were transported by either a pneumatic tube system or manual transport and analyzed either immediately or after 4 h. RESULTS: Pneumatic tube transported samples resulted in higher plasma potassium levels than manually transported samples. Serum potassium was lower than plasma potassium, confirming the suspicion of "reverse" pseudohyperkalemia. Letting the pneumatic tube transported samples stand on the bench for 4 h before centrifugation surprisingly resulted in decreased or unchanged plasma potassium. CONCLUSIONS: The reverse pseudohyperkalemia in heparin plasma samples from a CLL patient was caused by pneumatic tube transport. Our results suggest extracellular leakage of potassium, followed by active transport of potassium into intact leukemic cells. This is the first Swedish case of reverse pseudohyperkalemia in a CLL patient, where clinical suspicion of false hyperkalemia and awareness of the phenomenon lead to a rapid laboratory diagnosis. The demonstration of reverse pseudohyperkalemia prevented potentially dangerous medical interventions, such as potassium lowering treatment.
Asunto(s)
Heparina/metabolismo , Hiperpotasemia/sangre , Hiperpotasemia/prevención & control , Enfermedad Iatrogénica/prevención & control , Leucemia/sangre , Leucocitosis/sangre , Plasma/metabolismo , Anciano , Humanos , Leucemia Linfocítica Crónica de Células B/sangre , Recuento de Leucocitos , Masculino , Potasio/sangreAsunto(s)
Heparina/metabolismo , Hiperpotasemia/sangre , Leucocitosis/sangre , Leucocitosis/complicaciones , Leucemia-Linfoma Linfoblástico de Células T Precursoras/sangre , Leucemia-Linfoma Linfoblástico de Células T Precursoras/complicaciones , Preescolar , Reacciones Falso Positivas , Humanos , Hiperpotasemia/diagnóstico , Masculino , Potasio/sangreRESUMEN
BACKGROUND: Proteases of human pathogens are becoming increasingly important drug targets, hence it is necessary to understand their substrate specificity and to interpret this knowledge in practically useful ways. New methods are being developed that produce large amounts of cleavage information for individual proteases and some have been applied to extract cleavage rules from data. However, the hitherto proposed methods for extracting rules have been neither easy to understand nor very accurate. To be practically useful, cleavage rules should be accurate, compact, and expressed in an easily understandable way. RESULTS: A new method is presented for producing cleavage rules for viral proteases with seemingly complex cleavage profiles. The method is based on orthogonal search-based rule extraction (OSRE) combined with spectral clustering. It is demonstrated on substrate data sets for human immunodeficiency virus type 1 (HIV-1) protease and hepatitis C (HCV) NS3/4A protease, showing excellent prediction performance for both HIV-1 cleavage and HCV NS3/4A cleavage, agreeing with observed HCV genotype differences. New cleavage rules (consensus sequences) are suggested for HIV-1 and HCV NS3/4A cleavages. The practical usability of the method is also demonstrated by using it to predict the location of an internal cleavage site in the HCV NS3 protease and to correct the location of a previously reported internal cleavage site in the HCV NS3 protease. The method is fast to converge and yields accurate rules, on par with previous results for HIV-1 protease and better than previous state-of-the-art for HCV NS3/4A protease. Moreover, the rules are fewer and simpler than previously obtained with rule extraction methods. CONCLUSION: A rule extraction methodology by searching for multivariate low-order predicates yields results that significantly outperform existing rule bases on out-of-sample data, but are more transparent to expert users. The approach yields rules that are easy to use and useful for interpreting experimental data.
Asunto(s)
Interpretación Estadística de Datos , Péptido Hidrolasas/química , Péptido Hidrolasas/metabolismo , Inhibidores de Proteasas/química , Proteómica/métodos , Secuencia de Aminoácidos , Dominio Catalítico , Análisis por Conglomerados , Simulación por Computador , Bases de Datos de Proteínas , Proteasa del VIH/química , Proteasa del VIH/genética , Proteasa del VIH/metabolismo , Humanos , Péptido Hidrolasas/genética , Curva ROC , Reproducibilidad de los Resultados , Serina Endopeptidasas/química , Serina Endopeptidasas/genética , Serina Endopeptidasas/metabolismo , Proteínas no Estructurales Virales/química , Proteínas no Estructurales Virales/genética , Proteínas no Estructurales Virales/metabolismo , Proteínas Virales/química , Proteínas Virales/genética , Proteínas Virales/metabolismoRESUMEN
HIV-1 protease has a broad and complex substrate specificity, which hitherto has escaped a simple comprehensive definition. This, and the relatively high mutation rate of the retroviral protease, makes it challenging to design effective protease inhibitors. Several attempts have been made during the last two decades to elucidate the enigmatic cleavage specificity of HIV-1 protease and to predict cleavage of novel substrates using bioinformatic analysis methods. This review describes the methods that have been utilized to date to address this important problem and the results achieved. The data sets used are also reviewed and important aspects of these are highlighted.
Asunto(s)
Biología Computacional/métodos , Biología Computacional/tendencias , VIH-1/enzimología , Modelos Químicos , Péptido Hidrolasas/química , Péptido Hidrolasas/metabolismo , Humanos , Especificidad por Sustrato/fisiologíaRESUMEN
To investigate the role of neutrophil apoptosis in the pathogenesis of chronic neutropenia, we examined constitutive and death receptor-mediated apoptosis ex vivo of peripheral blood neutrophils obtained from six chronic idiopathic neutropenia (CIN) patients and six healthy adult blood donors. Apoptosis was quantified based on phosphatidylserine externalization and caspase-3 activation in freshly isolated neutrophils or after overnight cultivation of neutrophils in the absence or presence of pro- or anti-apoptotic factors, including the pan-caspase inhibitor, zVAD-fmk. Neutrophils from CIN patients receiving treatment with granulocyte colony-stimulating factor appeared to be more prone to constitutive apoptosis than cells from untreated patients; however, further investigations in larger cohorts of patients are needed to validate these pilot studies. Overall, the level of neutrophil apoptosis was similar in patient and control groups, thus supporting the notion that the underlying defect in these neutropenia patients lies elsewhere, such as in the bone marrow microenvironment.
Asunto(s)
Apoptosis/inmunología , Neutropenia/patología , Neutrófilos/metabolismo , Neutrófilos/patología , Receptores de Muerte Celular/fisiología , Adulto , Anciano de 80 o más Años , Células Cultivadas , Enfermedad Crónica , Femenino , Humanos , Masculino , Persona de Mediana Edad , Neutropenia/inmunología , Neutropenia/metabolismo , Neutrófilos/inmunología , Receptores de Muerte Celular/sangreRESUMEN
UNLABELLED: Congenital neutropenia in man was first reported 50 years ago by the Swedish paediatrician Rolf Kostmann. He coined the term "infantile genetic agranulocytosis" for this condition, which is now known as Kostmann syndrome. Recent studies have demonstrated a lack of antibacterial peptides and severe periodontitis in these patients despite recombinant growth factor treatment. Moreover, an increased degree of apoptosis of myeloid progenitor cells in the bone marrow has been shown. CONCLUSION: Future studies should aim to clarify the underlying molecular genetic defect in Kostmann syndrome.
Asunto(s)
Agranulocitosis/historia , Neutropenia/historia , Agranulocitosis/genética , Agranulocitosis/fisiopatología , Historia del Siglo XX , Humanos , Neutropenia/congénito , SueciaRESUMEN
Warts, hypogammaglobulinaemia, infections, myelokathexis (WHIM) syndrome is an inherited immune disorder associated with CXCR4 gene mutations. Recent studies suggested that impaired receptor downregulation and enhanced chemotactic responsiveness to stromal-derived factor-1 (SDF-1), the sole cognate ligand for CXCR4, may account for the characteristic features of WHIM patients. This study evaluated whether the interaction of SDF-1 with CXCR4 could block constitutive apoptosis of peripheral blood neutrophils from congenital neutropenia patients and controls. SDF-1 was found to be a potent anti-apoptotic factor for WHIM neutrophils harbouring a truncating CXCR4 mutation, but not for neutrophils from control individuals, thus supporting the notion that such mutations may confer enhanced functional responses.
Asunto(s)
Agammaglobulinemia/inmunología , Quimiocinas CXC/farmacología , Síndromes de Inmunodeficiencia/inmunología , Neutrófilos/patología , Receptores CXCR4/genética , Verrugas/inmunología , Adulto , Agammaglobulinemia/patología , Apoptosis/efectos de los fármacos , Estudios de Casos y Controles , Técnicas de Cultivo de Célula , Quimiocina CXCL12 , Femenino , Humanos , Síndromes de Inmunodeficiencia/patología , Infecciones/inmunología , Infecciones/patología , Mutación , Neutrófilos/metabolismo , Receptores CXCR4/metabolismo , Síndrome , Verrugas/patologíaRESUMEN
Rapidly developing viral resistance to licensed human immunodeficiency virus type 1 (HIV-1) protease inhibitors is an increasing problem in the treatment of HIV-infected individuals and AIDS patients. A rational design of more effective protease inhibitors and discovery of potential biological substrates for the HIV-1 protease require accurate models for protease cleavage specificity. In this study, several popular bioinformatic machine learning methods, including support vector machines and artificial neural networks, were used to analyze the specificity of the HIV-1 protease. A new, extensive data set (746 peptides that have been experimentally tested for cleavage by the HIV-1 protease) was compiled, and the data were used to construct different classifiers that predicted whether the protease would cleave a given peptide substrate or not. The best predictor was a nonlinear predictor using two physicochemical parameters (hydrophobicity, or alternatively polarity, and size) for the amino acids, indicating that these properties are the key features recognized by the HIV-1 protease. The present in silico study provides new and important insights into the workings of the HIV-1 protease at the molecular level, supporting the recent hypothesis that the protease primarily recognizes a conformation rather than a specific amino acid sequence. Furthermore, we demonstrate that the presence of 1 to 2 lysine residues near the cleavage site of octameric peptide substrates seems to prevent cleavage efficiently, suggesting that this positively charged amino acid plays an important role in hindering the activity of the HIV-1 protease.
Asunto(s)
Biología Computacional , Proteasa del VIH/genética , Proteasa del VIH/metabolismo , VIH-1/enzimología , Algoritmos , Inteligencia Artificial , Simulación por Computador , Proteasa del VIH/química , VIH-1/efectos de los fármacos , VIH-1/genética , Redes Neurales de la Computación , Especificidad por SustratoRESUMEN
Cathepsin G is a hematopoietic serine protease stored in the azurophil granules of neutrophil granulocytes. The mRNA of cathepsin G is transiently expressed during the promyelocyte stage of neutrophil maturation. The protease plays several roles in inflammatory actions of neutrophils, such as bactericidal effects. A human cathepsin G gene fragment of 6 kb directs a promyelocyte-specific expression in transgenic mice, indicating the presence of necessary cis-acting elements. However, neither the precise architecture of the promoter, nor the trans-acting factors responsible for its activation, have been characterized. In the present work, 2.6 kb upstream of the translation start site of the human cathepsin G gene was cloned. When transfected to monoblast-like U937 or to acute promyelocytic leukemia NB4 cells, both expressing endogenous cathepsin G, the initial 360 bp upstream of the translation start were sufficient to direct a strong expression of a luciferase reporter gene. No expression was observed in erythroid K562 control cells. Further deletions revealed three major regulatory regions containing the consensus binding-sites for the transcription factors C/EBP, c-myb and PU.1. Moreover, a GC-rich region, similar to a cis-element in the proteinase 3 promoter, was identified. Direct binding of the trans-factors C/EBPalpha, C/EBPepsilon, c-myb and PU.1 to the promoter was shown by chromatin immunoprecipitation. The functional significance of the cis-elements was verified by site-directed mutagenesis. Mutations of the putative PU.1 site moderately decreased the activity of the promoter in monoblastic U937 cells, but not in promyelocytic NB4 cells. Separate mutations of the putative C/EBP binding site, c-myb-binding site or the GC-rich element resulted in a dramatically reduced transcriptional activity in both cell lines, suggesting cooperation between corresponding trans-factors.
Asunto(s)
Catepsinas/genética , Proteínas de Unión al ADN/metabolismo , Regulación Neoplásica de la Expresión Génica , Células Mieloides/metabolismo , Regiones Promotoras Genéticas/genética , Serina Endopeptidasas/genética , Secuencia de Bases , Sitios de Unión/genética , Proteínas Potenciadoras de Unión a CCAAT/metabolismo , Catepsina G , Línea Celular Tumoral , Secuencia Rica en GC/genética , Humanos , Células K562 , Luciferasas/genética , Luciferasas/metabolismo , Datos de Secuencia Molecular , Mutagénesis Sitio-Dirigida , Mutación , Células Mieloides/patología , Proteínas Proto-Oncogénicas/metabolismo , Proteínas Proto-Oncogénicas c-myb/metabolismo , Proteínas Recombinantes de Fusión/genética , Proteínas Recombinantes de Fusión/metabolismo , Elementos de Respuesta/genética , Transactivadores/metabolismo , Sitio de Iniciación de la Transcripción , Transfección , Células U937RESUMEN
BACKGROUND AND OBJECTIVES: Human leukocyte elastase, proteinase 3 and cathepsin G are neutrophil granule proteins belonging to the hematopoietic serine protease superfamily. In addition to their established roles in inflammation, they have recently been implicated as regulators of granulopoiesis and mediators of apoptosis. We set out to characterize the individual biosynthetic profiles of these proteins in a neutrophil differentiation model. DESIGN AND METHODS: CD34+CD38+ hematopoietic progenitor cells from 21 healthy human bone marrow donors were cultured in vitro in the presence of recombinant human granulocyte colony-stimulating factor (G-CSF). Biosynthetic radiolabeling was performed in cells from 13 subjects after various periods of differentiation induction. Following protein extraction, the proteins were specifically immunoprecipitated from cell lysates and media and run in gel electrophoresis. Biosynthetic profiles of azurophil granule proteins, in particular members of the neutrophil serine protease family, were examined during myeloid differentiation. RESULTS: The onset of synthesis of myeloperoxidase, lysozyme, leukocyte elastase, and proteinase 3 occurred early after differentiation induction with G-CSF, while synthesis of cathepsin G, azurocidin, and bactericidal/permeability-increasing protein was detected somewhat later. Cathepsin G and proteinase 3 were retained intracellularly relatively efficiently, while leukocyte elastase and lysozyme were secreted to a greater extent. Cell morphology and positive immunocytochemistry for lactoferrin as well as flow cytometric analysis of selected surface antigens confirmed neutrophil-like maturation. INTERPRETATION AND CONCLUSIONS: We demonstrate that azurophil granule proteins, including proforms of human leukocyte elastase, proteinase 3 and cathepsin G, are constitutively secreted to various degrees during in vitro myeloid differentiation of human hematopoietic progenitor cells, in addition to being stored intracellularly in active forms. These findings suggest protein-specific sorting mechanisms and may have implications for the regulation of granulopoiesis.