Severe congenital neutropenia in a multigenerational family with a novel neutrophil elastase (ELANE) mutation

Reduced myeloid commitment and increased uptake by macrophages of stem cell-derived HPS2 neutrophils

Hermansky-Pudlak syndrome type 2 (HPS2) is a rare autosomal recessive disorder, caused by mutations in the AP3B1 gene, encoding the β3A subunit of the adapter protein complex 3. This results in mis-sorting of proteins within the cell. A clinical feature of HPS2 is severe neutropenia. Current HPS2 animal models do not recapitulate the human disease. Hence, we used induced pluripotent stem cells (iPSCs) of an HPS2 patient to study granulopoiesis. Development into CD15POS cells was reduced, but HPS2-derived CD15POS cells differentiated into segmented CD11b+CD16hi neutrophils. These HPS2 neutrophils phenocopied their circulating counterparts showing increased CD63 expression, impaired degranulation capacity, and intact NADPH oxidase activity. Most noticeable was the decrease in neutrophil yield during the final days of HPS2 iPSC cultures. Although neutrophil viability was normal, CD15NEG macrophages were readily phagocytosing neutrophils, contributing to the limited neutrophil output in HPS2. In this iPSC model, HPS2 neutrophil development is affected by a slower rate of development and by macrophage-mediated clearance during neutrophil maturation.

Sputum neutrophil elastase and its relation to pediatric bronchiectasis severity: A cross‐sectional study

Background and Aims

Sputum neutrophil elastase (NE) is a marker of neutrophilic airway inflammation in bronchiectasis. Yet, not much is known about its role in pediatric bronchiectasis severity. This study aimed to assess the sputum NE value as a biomarker of clinical and radiological severity in pediatric bronchiectasis.

Methods

This was a cross‐sectional study assessing sputum NE in a total of 50 bronchiectasis patients under the age of 18 years—30 patients with cystic fibrosis (CF) and 20 patients with non‐CF bronchiectasis were included. Bronchiectasis severity was assessed using Shwachman–Kulczycki (SK) score, CF‐ABLE score, and CF risk of disease progression score, among CF patients, and bronchiectasis severity index (BSI) and FACED criteria among non‐CF bronchiectasis patients, associations between sputum NE and bronchiectasis severity were assessed in both patient groups.

Results

Sputum NE was directly correlated with C‐reactive protein (r = 0.914, p < 0.001), (r = 0.786, p < 0.001), frequency of exacerbations (r = 0.852, p < 0.001) (r = 0.858, p < 0.001), exacerbations severity (r = 0.735, p = 0.002), (r = 0.907, p < 0.001), and the number of hospital admissions (r = 0.813, p < 0.001), (r = 0.612, p  =0.004) in the last year among CF, and non‐CF bronchiectasis patients, respectively. Additional linear correlations were found between sputum NE, CF risk of disease progression score (p < 0.001), CF‐ABLE score (p < 0.001), and lower forced expiratory volume 1% of predicted (p = 0.017; ρ = −0.8) among CF patients. Moreover, sputum NE was positively correlated with the neutrophil count (p = 0.018), and BSI severity score (p = 0.039; ρ = 0.465) among non‐CF bronchiectasis patients.

Conclusions

Sputum NE may be considered a good biomarker of bronchiectasis severity in both CF and non‐CF bronchiectasis patients, as confirmed by the exacerbations rate, CF risk of disease progression, and BSI scores.

Generation and characterization of a human iPSC line SANi007-A from a patient with a heterozygous dominant mutation in ELANE

Induced pluripotent stem cell (iPSC) line was generated from erythroblasts (EBLs) derived from a patient diagnosed with severe congenital neutropenia, caused by mutations in ELANE (c.614delG). Transgene-free iPSC line was generated using Sendai virus reprogramming. The iPSC line showed normal karyotype, expressed pluripotency associated genes and was capable of in vitro spontaneous differentiation towards the three germ layers. The generated iPSC line can be used to study severe congenital neutropenia and the role of neutrophil elastase protein.

The blood protein hCAP-18 in neutropenia: An 18-month experience of a new ELISA for clinical use

Neutropenia as an isolated clinical finding may include aetiologies ranging from severe disease to a transient condition, and differential diagnosis may be challenging. Previous data and clinical experience suggest that low levels of the neutrophil-derived protein human 18 kDa cathelicidin antimicrobial protein (hCAP-18) in the blood are predictive of more severe forms of neutropenia. The objective of this study was to present the results from a newly developed ELISA method that has been used in clinical routine in Sweden since 2018 for quantification of hCAP-18 in blood plasma. Using this method, we report that patients with severe disease analysed during the study period presented with low or undetectable levels of blood plasma hCAP-18, validating its use as screening tool for severe neutropenia. Furthermore, neutropenic patients as a group displayed lower levels of hCAP-18 as compared to blood donors. Within the group of neutropenic patients, those with neutrophil antibodies displayed significantly higher hCAP-18 levels compared to patients with idiopathic neutropenia. By including an analysis of hCAP-18 in the primary investigation of neutropenia, an increased accuracy in differential diagnosis is achieved, thus contributing to reduced costs of neutropenia management.

Cyclic Neutropenia From a Novel Mutation Ala57Asp of ELANE: Phenotypic Variability in Neutropenia From Mutated Ala57 Residue

ELANE-related neutropenia includes severe congenital neutropenia and cyclic neutropenia. Both are clinically characterized by recurrent fever, skin and oropharyngeal inflammation. We report a novel mutation in ELANE in a 20-year-old man with a history of self-limiting febrile episodes and neutropenia with a cyclic pattern since 7 years of age. Direct sequencing analysis of ELANE revealed he was heterozygous for a novel missense mutation (p.Ala57Asp). The Ala57 residue is a mutation hotspot, and all previously reported missense mutations (Ala57Ser/Thr/Val) were observed in severe congenital neutropenia cases. Thus, the present case demonstrates a phenotypic variability in ELANE-related neutropenia from mutated Ala57.

Extended Cleavage Specificity of Human Neutrophil Elastase, Human Proteinase 3, and Their Distant Ortholog Clawed Frog PR3-Three Elastases With Similar Primary but Different Extended Specificities and Stability

Serine proteases are major granule constituents of several of the human hematopoietic cell lineages. Four proteolytically active such proteases have been identified in human neutrophils: cathepsin G (hCG), N-elastase (hNE), proteinase 3 (hPR-3), and neutrophil serine protease 4 (hNSP-4). Here we present the extended cleavage specificity of two of the most potent and most abundant of these enzymes, hNE and hPR-3. Their extended specificities were determined by phage display and by the analysis of a panel of chromogenic and recombinant substrates. hNE is an elastase with a relatively broad specificity showing a preference for regions containing several aliphatic amino acids. The protease shows self-cleaving activity, which results in the loss of activity during storage even at +4°C. Here we also present the extended cleavage specificity of hPR-3. Compared with hNE, it shows considerably lower proteolytic activity. However, it is very stable, shows no self-cleaving activity and is actually more active in the presence of SDS, possibly by enhancing the accessibility of the target substrate. This enables specific analysis of hPR-3 activity even in the presence of all the other neutrophil enzymes with addition of 1% SDS. Neutrophils are the most abundant white blood cell in humans and one of the key players in our innate immune defense. The neutrophil serine proteases are very important for the function of the neutrophils and therefore also interesting from an evolutionary perspective. In order to study the origin and functional conservation of these neutrophil proteases we have identified and cloned an amphibian ortholog, Xenopus PR-3 (xPR-3). This enzyme was found to have a specificity very similar to hPR-3 but did not show the high stability in the presence of SDS. The presence of an elastase in Xenopus closely related to hPR-3 indicates a relatively early appearance of these enzymes during vertebrate evolution.

Neutrophil serine proteases in antibacterial defense

Neutrophil serine proteases (NSPs) are critical for the effective functioning of neutrophils and greatly contribute to immune protection against bacterial infections. Thanks to their broad substrate specificity, these chymotrypsin-like proteases trigger multiple reactions that are detrimental to bacterial survival such as direct bacterial killing, generation of antimicrobial peptides, inactivation of bacterial virulence factors and formation of neutrophil extracellular traps. Recently, the importance of NSPs in antibacterial defenses has been further underscored by discoveries of unique bacterial evasion strategies to combat these proteases. Bacteria can indirectly disarm NSPs by protecting bacterial substrates against NSP cleavage, but also produce inhibitory molecules that potently block NSPs. Here we review recent insights in the functional contribution of NSPs in host protection against bacterial infections and the elegant strategies that bacteria use to counteract these responses.

Educational paper: Defects in number and function of neutrophilic granulocytes causing primary immunodeficiency

The neutrophilic granulocyte (neutrophil) is the most important cellular component of the innate immune system. A total absence of neutrophils or a significant decrease in their number leads to severe immunodeficiency. A mature neutrophil, released from the bone marrow, should be able to migrate from the blood towards the tissues, following a chemotactic gradient to a pathogen. In order to be neutralized, this pathogen has to be recognized, phagocytosed, and destroyed by lytic enzymes contained in the neutrophil's granules and reactive oxygen species formed by the enzyme complex NADPH oxidase. Rare genetic defects leading to the loss of each one of these biological properties of the neutrophil have been described and are associated with immunodeficiency. This review provides a summary of the normal development and biological functions of neutrophils and describes the diseases caused by defects in neutrophil number and function.