Human DOCK2 Deficiency: Report of a Novel Mutation and Evidence for Neutrophil Dysfunction.

DOCK2 is a guanine-nucleotide-exchange factor for Rac proteins. Activated Rac serves various cellular functions including the reorganization of the actin cytoskeleton in lymphocytes and neutrophils and production of reactive oxygen species in neutrophils. Since 2015, six unrelated patients with combined immunodeficiency and early-onset severe viral infections caused by bi-allelic loss-of-function mutations in DOCK2 have been described. Until now, the function of phagocytes, specifically neutrophils, has not been assessed in human DOCK2 deficiency. Here, we describe a new kindred with four affected siblings harboring a homozygous splice-site mutation (c.2704-2 A > C) in DOCK2. The mutation results in alternative splicing and a complete loss of DOCK2 protein expression. The patients presented with leaky severe combined immunodeficiency or Omenn syndrome. The novel mutation affects EBV-B cell migration and results in NK cell dysfunction similar to previous observations. Moreover, both cytoskeletal rearrangement and reactive oxygen species production are partially impaired in DOCK2-deficient neutrophils.

Severe glucose-6-phosphate dehydrogenase deficiency leads to susceptibility to infection and absent NETosis.

BACKGROUND: Glucose-6-phosphate dehydrogenase (G6PD) deficiency is the most common enzymatic disorder of red blood cells in human subjects, causing hemolytic anemia linked to impaired nicotinamide adenine dinucleotide phosphate (NADPH) production and imbalanced redox homeostasis in erythrocytes. Because G6PD is expressed by a variety of hematologic and nonhematologic cells, a broader clinical phenotype could be postulated in G6PD-deficient patients. We describe 3 brothers with severe G6PD deficiency and susceptibility to bacterial infection. OBJECTIVE: We sought to study the molecular pathophysiology leading to susceptibility to infection in 3 siblings with severe G6PD deficiency. METHODS: Blood samples of 3 patients with severe G6PD deficiency were analyzed for G6PD enzyme activity, cellular oxidized nicotinamide adenine dinucleotide phosphate/NADPH levels, phagocytic reactive oxygen species production, neutrophil extracellular trap (NET) formation, and neutrophil elastase translocation. RESULTS: In these 3 brothers strongly reduced NADPH oxidase function was found in granulocytes, leading to impaired NET formation. Defective NET formation has thus far been only observed in patients with the NADPH oxidase deficiency chronic granulomatous disease, who require antibiotic and antimycotic prophylaxis to prevent life-threatening bacterial and fungal infections. CONCLUSION: Because severe G6PD deficiency can be a phenocopy of chronic granulomatous disease with regard to the cellular and clinical phenotype, careful evaluation of neutrophil function seems mandatory in these patients to decide on appropriate anti-infective preventive measures. Determining the level of G6PD enzyme activity should be followed by analysis of reactive oxygen species production and NET formation to decide on required antibiotic and antimycotic prophylaxis.

Modern management of phagocyte defects.

Phagocytic neutrophil granulocytes are among the first immune cells active at sites of infection, forming an important first-line defense against invading microorganisms. Congenital immune defects concerning these phagocytes may be due to reduced neutrophil numbers or function. Management of affected patients depends on the type and severity of disease. Here, we provide an overview of causes and treatment of diseases associated with congenital neutropenia, as well as defects of the phagocytic respiratory burst.

Hyperinflammation in patients with chronic granulomatous disease leads to impairment of hematopoietic stem cell functions.

BACKGROUND: Defects in phagocytic nicotinamide adenine dinucleotide phosphate oxidase 2 (NOX2) function cause chronic granulomatous disease (CGD), a primary immunodeficiency characterized by dysfunctional microbicidal activity and chronic inflammation. OBJECTIVE: We sought to study the effect of chronic inflammation on the hematopoietic compartment in patients and mice with X-linked chronic granulomatous disease (X-CGD). METHODS: We used immunostaining and functional analyses to study the hematopoietic compartment in patients with CGD. RESULTS: An analysis of bone marrow cells from patients and mice with X-CGD revealed a dysregulated hematopoiesis characterized by increased numbers of hematopoietic progenitor cells (HPCs) at the expense of repopulating hematopoietic stem cells (HSCs). In patients with X-CGD, there was a clear reduction in the proportion of HSCs in bone marrow and peripheral blood, and they were also more rapidly exhausted after in vitro culture. In mice with X-CGD, increased cycling of HSCs, expansion of HPCs, and impaired long-term engraftment capacity were found to be associated with high concentrations of proinflammatory cytokines, including IL-1ß. Treatment of wild-type mice with IL-1ß induced enhanced cell-cycle entry of HSCs, expansion of HPCs, and defects in long-term engraftment, mimicking the effects observed in mice with X-CGD. Inhibition of cytokine signaling in mice with X-CGD reduced HPC numbers but had only minor effects on the repopulating ability of HSCs. CONCLUSIONS: Persistent chronic inflammation in patients with CGD is associated with hematopoietic proliferative stress, leading to a decrease in the functional activity of HSCs. Our observations have clinical implications for the development of successful autologous cell therapy approaches.

Gene editing of NCF1 loci is associated with homologous recombination and chromosomal rearrangements.

CRISPR-based genome editing of pseudogene-associated disorders, such as p47phox-deficient chronic granulomatous disease (p47 CGD), is challenged by chromosomal rearrangements due to presence of multiple targets. We report that interactions between highly homologous sequences that are localized on the same chromosome contribute substantially to post-editing chromosomal rearrangements. We successfully employed editing approaches at the NCF1 gene and its pseudogenes, NCF1B and NCF1C, in a human cell line model of p47 CGD and in patient-derived human hematopoietic stem and progenitor cells. Upon genetic engineering, a droplet digital PCR-based method identified cells with altered copy numbers, spanning megabases from the edited loci. We attributed the high aberration frequency to the interaction between repetitive sequences and their predisposition to recombination events. Our findings emphasize the need for careful evaluation of the target-specific genomic context, such as the presence of homologous regions, whose instability can constitute a risk factor for chromosomal rearrangements upon genome editing.

Targeted knock-in of NCF1 cDNA into the NCF2 locus leads to myeloid phenotypic correction of p47 phox -deficient chronic granulomatous disease.

p47 phox -deficient chronic granulomatous disease (p47-CGD) is a primary immunodeficiency caused by mutations in the neutrophil cytosolic factor 1 (NCF1) gene, resulting in defective NADPH oxidase function in phagocytes. Due to its complex genomic context, the NCF1 locus is not suited for safe gene editing with current genome editing technologies. Therefore, we developed a targeted NCF1 coding sequence knock-in by CRISPR-Cas9 ribonucleoprotein and viral vector template delivery, to restore p47 phox expression under the control of the endogenous NCF2 locus. NCF2 encodes for p67 phox , an NADPH oxidase subunit that closely interacts with p47 phox and is predominantly expressed in myeloid cells. This approach restored p47 phox expression and NADPH oxidase function in p47-CGD patient hematopoietic stem and progenitor cells (HSPCs) and in p47 phox -deficient mouse HSPCs, with the transgene expression following a myeloid differentiation pattern. Adeno-associated viral vectors performed favorably over integration-deficient lentiviral vectors for template delivery, with fewer off-target integrations and higher correction efficacy in HSPCs. Such myeloid-directed gene editing is promising for clinical CGD gene therapy, as it leads to the co-expression of p47 phox and p67 phox , ensuring spatiotemporal and near-physiological transgene expression in myeloid cells.

Derivation and functional analysis of patient-specific induced pluripotent stem cells as an in vitro model of chronic granulomatous disease.

Chronic granulomatous disease (CGD) is an inherited disorder of phagocytes in which NADPH oxidase is defective in generating reactive oxygen species. In this study, we reprogrammed three normal unrelated patient's fibroblasts (p47(phox) and gp91(phox) ) to pluripotency by lentiviral transduction with defined pluripotency factors. These induced pluripotent stem cells (iPSC) share the morphological features of human embryonic stem cells, express the key pluripotency factors, and possess high telomerase activity. Furthermore, all the iPSC lines formed embryoid bodies in vitro containing cells originating from all three germ layers and were capable of teratoma formation in vivo. They were isogenic with the original patient fibroblasts, exhibited normal karyotype, and retained the p47(phox) or gp91(pho) (x) mutations found in the patient fibroblasts. We further demonstrated that these iPSC could be differentiated into monocytes and macrophages with a similar cytokine profile to blood-derived macrophages under resting conditions. Most importantly, CGD-patient-specific iPSC-derived macrophages showed normal phagocytic properties but lacked reactive oxygen species production, which correlates with clinical diagnosis of CGD in the patients. Together these results suggest that CGD-patient-specific iPSC lines represent an important tool for modeling CGD disease phenotypes, screening candidate drugs, and the development of gene therapy.

Correction of X-linked chronic granulomatous disease by gene therapy, augmented by insertional activation of MDS1-EVI1, PRDM16 or SETBP1.

Gene transfer into hematopoietic stem cells has been used successfully for correcting lymphoid but not myeloid immunodeficiencies. Here we report on two adults who received gene therapy after nonmyeloablative bone marrow conditioning for the treatment of X-linked chronic granulomatous disease (X-CGD), a primary immunodeficiency caused by a defect in the oxidative antimicrobial activity of phagocytes resulting from mutations in gp91(phox). We detected substantial gene transfer in both individuals' neutrophils that lead to a large number of functionally corrected phagocytes and notable clinical improvement. Large-scale retroviral integration site-distribution analysis showed activating insertions in MDS1-EVI1, PRDM16 or SETBP1 that had influenced regulation of long-term hematopoiesis by expanding gene-corrected myelopoiesis three- to four-fold in both individuals. Although insertional influences have probably reinforced the therapeutic efficacy in this trial, our results suggest that gene therapy in combination with bone marrow conditioning can be successfully used to treat inherited diseases affecting the myeloid compartment such as CGD.

Restoration of anti-Aspergillus defense by neutrophil extracellular traps in human chronic granulomatous disease after gene therapy is calprotectin-dependent.

BACKGROUND: Aspergillus spp infection is a potentially lethal disease in patients with neutropenia or impaired neutrophil function. We showed previously that Aspergillus hyphae, too large for neutrophil phagocytosis, are inhibited by reactive oxygen species-dependent neutrophil extracellular trap (NET) formation. This process is defective in chronic granulomatous disease (CGD) because of impaired phagocyte nicotinamide adenine dinucleotide phosphate (NADPH) oxidase function. OBJECTIVE: To determine the antifungal agent and mechanism responsible for reconstitution of Aspergillus growth inhibition within NETs after complementation of NADPH oxidase function by gene therapy (GT) for CGD. METHODS: Antifungal activity of free and NET-released calprotectin was assessed by incubation of Aspergillus nidulans with purified calprotectin, induced NETs from human controls, and CGD neutrophils after GT in the presence or absence of Zn(2+) or α-S100A9 antibody, and with induced NETs from wild-type or S100A9(-/-) mouse neutrophils. RESULTS: We identified the host Zn(2+) chelator calprotectin as a neutrophil-associated antifungal agent expressed within NETs, reversibly preventing A nidulans growth at low concentrations, and leading to irreversible fungal starvation at higher concentrations. Specific antibody-blocking and Zn(2+) addition abolished calprotectin-mediated inhibition of A nidulans proliferation in vitro. The role of calprotectin in anti-Aspergillus defense was confirmed in calprotectin knockout mice. CONCLUSION: Reconstituted NET formation by GT for human CGD was associated with rapid cure of pre-existing therapy-refractory invasive pulmonary aspergillosis in vivo, underlining the role of functional NADPH oxidase in NET formation and calprotectin release for antifungal activity. These results demonstrate the critical role of calprotectin in human innate immune defense against Aspergillus infection.

Restoration of NET formation by gene therapy in CGD controls aspergillosis.

Chronic granulomatous disease (CGD) patients have impaired nicotinamide adenine dinucleotide phosphate (NADPH) oxidase function, resulting in poor antimicrobial activity of neutrophils, including the inability to generate neutrophil extracellular traps (NETs). Invasive aspergillosis is the leading cause of death in patients with CGD; it is unclear how neutrophils control Aspergillus species in healthy persons. The aim of this study was to determine whether gene therapy restores NET formation in CGD by complementation of NADPH oxidase function, and whether NETs have antimicrobial activity against Aspergillus nidulans. Here we show that reconstitution of NET formation by gene therapy in a patient with CGD restores neutrophil elimination of A nidulans conidia and hyphae and is associated with rapid cure of preexisting therapy refractory invasive pulmonary aspergillosis, underlining the role of functional NADPH oxidase in NET formation and antifungal activity.

Membrane Dynamics and Organization of the Phagocyte NADPH Oxidase in PLB-985 Cells.

Neutrophils are the first cells recruited at the site of infections, where they phagocytose the pathogens. Inside the phagosome, pathogens are killed by proteolytic enzymes that are delivered to the phagosome following granule fusion, and by reactive oxygen species (ROS) produced by the NADPH oxidase. The NADPH oxidase complex comprises membrane proteins (NOX2 and p22phox), cytoplasmic subunits (p67phox, p47phox, and p40phox) and the small GTPase Rac. These subunits assemble at the phagosomal membrane upon phagocytosis. In resting neutrophils the catalytic subunit NOX2 is mainly present at the plasma membrane and in the specific granules. We show here that NOX2 is also present in early and recycling endosomes in human neutrophils and in the neutrophil-like cell line PLB-985 expressing GFP-NOX2. In the latter cells, an increase in NOX2 at the phagosomal membrane was detected by live-imaging after phagosome closure, probably due to fusion of endosomes with the phagosome. Using super-resolution microscopy in PLB-985 WT cells, we observed that NOX2 forms discrete clusters in the plasma membrane. The number of clusters increased during frustrated phagocytosis. In PLB-985NCF1ΔGT cells that lack p47phox and do not assemble a functional NADPH oxidase, the number of clusters remained stable during phagocytosis. Our data suggest a role for p47phox and possibly ROS production in NOX2 recruitment at the phagosome.

CRISPR-Directed Therapeutic Correction at the NCF1 Locus Is Challenged by Frequent Incidence of Chromosomal Deletions.

Resurrection of non-processed pseudogenes may increase the efficacy of therapeutic gene editing, upon simultaneous targeting of a mutated gene and its highly homologous pseudogenes. To investigate the potency of this approach for clinical gene therapy of human diseases, we corrected a pseudogene-associated disorder, the immunodeficiency p47 phox -deficient chronic granulomatous disease (p47 phox CGD), using clustered regularly interspaced short palindromic repeats-associated nuclease Cas9 (CRISPR-Cas9) to target mutated neutrophil cytosolic factor 1 (NCF1). Being separated by less than two million base pairs, NCF1 and two pseudogenes are closely co-localized on chromosome 7. In healthy people, a two-nucleotide GT deletion (ΔGT) is present in the NCF1B and NCF1C pseudogenes only. In the majority of patients with p47 phox CGD, the NCF1 gene is inactivated due to a ΔGT transfer from one of the two non-processed pseudogenes. Here we demonstrate that concurrent targeting and correction of mutated NCF1 and its pseudogenes results in therapeutic CGD phenotype correction, but also causes potentially harmful chromosomal deletions between the targeted loci in a p47 phox -deficient CGD cell line model. Therefore, development of genome-editing-based treatment of pseudogene-related disorders mandates thorough safety examination, as well as technological advances, limiting concurrent induction of multiple double-strand breaks on a single chromosome.

Actinomyces in chronic granulomatous disease: an emerging and unanticipated pathogen.

BACKGROUND: Chronic granulomatous disease (CGD) is a rare inherited disease of the phagocyte NADPH oxidase system that causes defective production of toxic oxygen metabolites, impaired bacterial and fungal killing, and recurrent life-threatening infections, mostly by catalase-producing organisms. We report for the first time, to our knowledge, chronic infections with Actinomyces species in 10 patients with CGD. Actinomycosis is a chronic granulomatous condition that commonly manifests as cervicofacial, pulmonary, or abdominal disease, caused by slowly progressive infection with oral and gastrointestinal commensal Actinomyces species. Treatment of actinomycosis is usually simple in immunocompetent individuals, requiring long-term, high-dose intravenous penicillin, but is more complicated in those with CGD because of delayed diagnosis and an increased risk of chronic invasive or debilitating disease. METHODS: Actinomyces was identified by culture, staining, 16S ribosomal DNA polymerase chain reaction, and/or a complement fixation test in 10 patients with CGD. RESULTS: All 10 patients presented with a history of fever and elevated inflammatory signs without evident focus. Diagnosis was delayed and clinical course severe and protracted despite high-dose intravenous antibiotic therapy and/or surgery. These results suggest an unrecognized and unanticipated susceptibility to weakly pathogenic Actinomyces species in patients with CGD because these are catalase-negative organisms previously thought to be nonpathogenic in CGD. CONCLUSIONS: Actinomycosis should be vigorously sought and promptly treated in patients with CGD presenting with uncommon and prolonged clinical signs of infection. Actinomycosis is a catalase-negative infection important to consider in CGD.

Novel Diagnostic Tool for p47 phox -Deficient Chronic Granulomatous Disease Patient and Carrier Detection.

Chronic granulomatous disease (CGD) is a primary immunodeficiency caused by mutations of the phagocytic nicotinamide adenine dinucleotide phosphate (NADPH) oxidase. Autosomal recessive p47 phox -deficient CGD (p47 phox CGD) is the second most frequent form of the disease in western countries, and more than 94% of patients have a disease-causing dinucleotide deletion (ΔGT) in the neutrophil cytosolic factor 1 (NCF1) gene. The ΔGT mutation is most likely transferred onto the NCF1 from one of its two pseudogenes co-localized on the same chromosome. The presence of NCF1 pseudogenes in healthy individuals makes the genetic diagnostics of ΔGT p47 phox CGD challenging, as it requires the distinction between ΔGT in NCF1 and in the two pseudogenes. We have developed a diagnostic tool for the identification of p47 phox CGD based on PCR co-amplification of NCF1 and its pseudogenes, followed by band intensity quantification of restriction fragment length polymorphism products. The single-day, reliable p47 phox CGD diagnostics allow for robust discrimination of homozygous ΔGT p47phox CGD patients from heterozygous carriers and healthy individuals, as well as for monitoring gene therapy efficacy.

High Levels of IL-18 and IFN-γ in Chronically Inflamed Tissue in Chronic Granulomatous Disease.

Background: Chronic granulomatous disease (CGD) is caused by a malfunctioning nicotinamide adenine dinucleotide phosphate (NADPH) oxidase complex in phagocytes, leading to impaired bacterial and fungal killing and hyperinflammation. Objective: To characterize macrophage subsets and cytokine/chemokine signaling loops involved in CGD tissue hyperinflammation. Methods: Cytokine/chemokine production and surface marker expression were analyzed in inflamed tissue of four CGD patients and compared to cytokine/chemokine released by CGD macrophages upon priming to different macrophage subpopulations. Furthermore, the re-priming capacity of CGD pro-inflammatory M1 to M2a anti-inflammatory macrophages was evaluated. Results: In human CGD inflammatory tissue, IL-18 and IFN-γ were detected in significant quantity. Immunofluorescence analysis identified macrophages as one source of IL-18 in inflamed tissue. In vitro, CGD macrophages could be primed and re-primed into all inflammatory/anti-inflammatory macrophage subpopulations. IL-18 was also released by M1 CGD and control macrophages. Conclusion: CGD pro-inflammatory M1 macrophages remain M1 primed in vivo. As CGD M1 macrophages can be re-primed to anti-inflammatory M2a phenotype in vitro, macrophages are kept in M1 state in vivo by a persistent pro-inflammatory environment. Our results suggest a paracrine signaling loop between M1 macrophage derived IL-18 and non-macrophage derived IFN-γ maintaining macrophage pro-inflammatory activity in CGD tissue.

Lentiviral gene therapy vector with UCOE stably restores function in iPSC-derived neutrophils of a CDG patient.

A recent gamma-retroviral clinical Chronic Granulomatous Disease (CGD) gene therapy (GT) trial achieved proof-of-concept but was accompanied by activation of oncogenes and transgene silencing. The ubiquitous chromatin opening element (UCOE) comprises the sequences of two divergently oriented house-keeping gene promoters and is known to have anti-silencing properties. In a screen we identified two novel UCOE constructs that prevent adjacent promoter methylation in P19 cells. Experiments were continued with the shorter UCOE constructs in induced pluripotent stem cells (iPSC) derived from a p47phox-deficient CGD patient. The iPSC line was transduced with the lentiviral GT vectors expressing P47 under the constitutively active SFFV promoter with UCOE element (UCOE_SF) and without UCOE element (SF) adjacent to the SFFV promoter. The iPSC were expanded before propagation towards neutrophils. 20 days after transduction the UCOE_SF vector was protected from methylation in iPSC as previously shown in P19 cells, whereas the SF vector was heavily methylated in iPSC. The UCOE_SF vector maintained stable transgene expression in iPSC, macrophages and neutrophils, whereas the SF vector was strongly silenced. The UCOE_SF vector stably restored ROS production in neutrophils, whereas for the SF vector the count of ROS producing cells was marginal. To conclude, we have shown that the prevention of transgene silencing by UCOE is functionally and mechanistically preserved upon terminal neutrophil differentiation.

Advances in the treatment of Chronic Granulomatous Disease by gene therapy.

Gene transfer into hematopoietic stem cells has been successfully used to correct immunodeficiencies affecting the lymphoid compartment. However, similar results have not been reported for diseases affecting myeloid cells, mainly due to low engraftment levels of gene-modified cells observed in unconditioned patients. Here we review the developments leading to a gene therapy approach for the treatment of Chronic Granulomatous Disease (CGD), a primary life threatening immunodeficiency caused by a defect in the oxidative antimicrobial activity of phagocytes. Although the disease can be cured by bone marrow transplantation, this treatment is only available to patients with HLA-identical sibling or matched unrelated donors. One therapeutic option for patients without suitable donor is the genetic modification of autologous hematopoietic stem cells. Although early attempts to correct CGD by gene therapy were unsuccessful, these studies demonstrated the safety and limitations of gene transfer into hematopoietic stem cells (HSC) of CGD patients using retroviral vectors. The recent development of advanced gene transduction protocols together with improved retroviral vectors, combined with low intensity chemotherapy conditioning, allowed partial correction of the granulocytic function with a significant clinical benefit in treated patients. These results may have important implications for future applications of gene therapy in myeloid disorders and inherited diseases using hematopoietic stem cells.

CRISPR/Cas9-generated p47phox-deficient cell line for Chronic Granulomatous Disease gene therapy vector development.

Development of gene therapy vectors requires cellular models reflecting the genetic background of a disease thus allowing for robust preclinical vector testing. For human p47phox-deficient chronic granulomatous disease (CGD) vector testing we generated a cellular model using clustered regularly interspaced short palindromic repeats (CRISPR)/Cas9 to introduce a GT-dinucleotide deletion (ΔGT) mutation in p47phox encoding NCF1 gene in the human acute myeloid leukemia PLB-985 cell line. CGD is a group of hereditary immunodeficiencies characterized by impaired respiratory burst activity in phagocytes due to a defective phagocytic nicotinamide adenine dinucleotide phosphate (NADPH) oxidase. In Western countries autosomal-recessive p47phox-subunit deficiency represents the second largest CGD patient cohort with unique genetics, as the vast majority of p47phox CGD patients carries ΔGT deletion in exon two of the NCF1 gene. The established PLB-985 NCF1 ΔGT cell line reflects the most frequent form of p47phox-deficient CGD genetically and functionally. It can be differentiated to granulocytes efficiently, what creates an attractive alternative to currently used iPSC models for rapid testing of novel gene therapy approaches.

Non-invasive near-infrared fluorescence imaging of the neutrophil response in a mouse model of transient cerebral ischaemia.

Near-infrared fluorescence (NIRF) imaging enables non-invasive monitoring of molecular and cellular processes in live animals. Here we demonstrate the suitability of NIRF imaging to investigate the neutrophil response in the brain after transient middle cerebral artery occlusion (tMCAO). We established procedures for ex vivo fluorescent labelling of neutrophils without affecting their activation status. Adoptive transfer of labelled neutrophils in C57BL/6 mice before surgery resulted in higher fluorescence intensities over the ischaemic hemisphere in tMCAO mice with NIRF imaging when compared with controls, corroborated by ex vivo detection of labelled neutrophils using fluorescence microscopy. NIRF imaging showed that neutrophils started to accumulate immediately after tMCAO, peaking at 18 h, and were still visible until 48 h after reperfusion. Our data revealed accumulation of neutrophils also in extracranial tissue, indicating damage in the external carotid artery territory in the tMCAO model. Antibody-mediated inhibition of α4-integrins did reduce fluorescence signals at 18 and 24, but not at 48 h after reperfusion, compared with control treatment animals. Antibody treatment reduced cerebral lesion volumes by 19%. In conclusion, the non-invasive nature of NIRF imaging allows studying the dynamics of neutrophil recruitment and its modulation by targeted interventions in the mouse brain after transient experimental cerebral ischaemia.