CD11c-expressing microglia are transient, driven by interactions with apoptotic cells.

Microglia, the parenchymal macrophage of the central nervous system serve crucial remodeling functions throughout development. Microglia are transcriptionally heterogenous, suggesting that distinct microglial states confer discrete roles. Currently, little is known about how dynamic these states are, the cues that promote them, or how they impact microglial function. In the developing retina, we previously found a significant proportion of microglia express CD11c (Integrin αX, complement receptor 4, Itgax) which has also been reported in other developmental and disease contexts. Here, we sought to understand the regulation and function of CD11c+ microglia. We found that CD11c+ microglia track with prominent waves of neuronal apoptosis in postnatal retina. Using genetic fate mapping, we provide evidence that microglia transition out of the CD11c state to return to homeostasis. We show that CD11c+ microglia have elevated lysosomal content and contribute to the clearance of apoptotic neurons, and found that acquisition of CD11c expression is, in part, dependent upon the TAM receptor Axl. Using selective ablation, we found CD11c+ microglia are not uniquely critical for phagocytic clearance of apoptotic cells. Together, our data suggest CD11c+ microglia are a transient state induced by developmental apoptosis rather than a specialized subset mediating phagocytic elimination.

Type-I-interferon-responsive microglia shape cortical development and behavior.

Microglia are brain-resident macrophages that shape neural circuit development and are implicated in neurodevelopmental diseases. Multiple microglial transcriptional states have been defined, but their functional significance is unclear. Here, we identify a type I interferon (IFN-I)-responsive microglial state in the developing somatosensory cortex (postnatal day 5) that is actively engulfing whole neurons. This population expands during cortical remodeling induced by partial whisker deprivation. Global or microglial-specific loss of the IFN-I receptor resulted in microglia with phagolysosomal dysfunction and an accumulation of neurons with nuclear DNA damage. IFN-I gain of function increased neuronal engulfment by microglia in both mouse and zebrafish and restricted the accumulation of DNA-damaged neurons. Finally, IFN-I deficiency resulted in excess cortical excitatory neurons and tactile hypersensitivity. These data define a role for neuron-engulfing microglia during a critical window of brain development and reveal homeostatic functions of a canonical antiviral signaling pathway in the brain.

Ethambutol and visual assessment in England: current practice and recommendations.

BACKGROUND: Standard treatment for tuberculosis (TB) in children and adults includes an initial two-month course of ethambutol, a drug that in rare cases can cause optic neuropathy and irreversible vision loss. There is a lack of clear guidance on what vision assessments are needed before and during treatment with ethambutol, with the Royal College of Ophthalmologists, National Institute for Health and Care Excellence, British National Formulary and British Thoracic Society offering different guidance. We aimed to assess how vision is routinely tested in patients treated with ethambutol in TB services across England. METHODS: An online survey developed by Public Health England was sent to all TB services in England in 2018 to assess current practice and inform the development of best practice recommendations for visual assessment of patients treated with ethambutol for TB. RESULTS: Sixty-six TB professionals from across England responded, a response rate of 54%. The results showed variations in practice, including when to omit ethambutol from treatment, the timing and frequency of visual assessment, the type of visual assessment, referral processes and management of visual changes. CONCLUSION: This national survey highlights the need for clear guidelines on the testing of vision for patients taking ethambutol at recommended doses, before and during treatment. We suggest a pragmatic approach to visual assessment to reduce variation in practice, proposing a stepwise pathway for patients on standard TB treatment for local adaptation.

Drivers determining tuberculosis disease screening yield in four European screening programmes: a comparative analysis.

BACKGROUND: The World Health Organization End TB Strategy emphasises screening for early diagnosis of tuberculosis (TB) in high-risk groups, including migrants. We analysed key drivers of TB yield differences in four large migrant TB screening programmes to inform TB control planning and feasibility of a European approach. METHODS: We pooled individual TB screening episode data from Italy, the Netherlands, Sweden and the UK, and analysed predictors and interactions for TB case yield using multivariable logistic regression models. RESULTS: Between 2005 and 2018 in 2 302 260 screening episodes among 2 107 016 migrants to four countries, the programmes identified 1658 TB cases (yield 72.0 (95% CI 68.6-75.6) per 100 000). In logistic regression analysis, we found associations between TB screening yield and age (≥55 years: OR 2.91 (95% CI 2.24-3.78)), being an asylum seeker (OR 3.19 (95% CI 1.03-9.83)) or on a settlement visa (OR 1.78 (95% CI 1.57-2.01)), close TB contact (OR 12.25 (95% CI 11.73-12.79)) and higher TB incidence in the country of origin. We demonstrated interactions between migrant typology and age, as well as country of origin. For asylum seekers, the elevated TB risk remained similar above country of origin incidence thresholds of 100 per 100 000. CONCLUSIONS: Key determinants of TB yield included close contact, increasing age, incidence in country of origin and specific migrant groups, including asylum seekers and refugees. For most migrants such as UK students and workers, TB yield significantly increased with levels of incidence in the country of origin. The high, country of origin-independent TB risk in asylum seekers above a 100 per 100 000 threshold could reflect higher transmission and re-activation risk of migration routes, with implications for selecting populations for TB screening.

Type I interferon responsive microglia shape cortical development and behavior.

Microglia are brain resident phagocytes that can engulf synaptic components and extracellular matrix as well as whole neurons. However, whether there are unique molecular mechanisms that regulate these distinct phagocytic states is unknown. Here we define a molecularly distinct microglial subset whose function is to engulf neurons in the developing brain. We transcriptomically identified a cluster of Type I interferon (IFN-I) responsive microglia that expanded 20-fold in the postnatal day 5 somatosensory cortex after partial whisker deprivation, a stressor that accelerates neural circuit remodeling. In situ, IFN-I responsive microglia were highly phagocytic and actively engulfed whole neurons. Conditional deletion of IFN-I signaling (Ifnar1fl/fl) in microglia but not neurons resulted in dysmorphic microglia with stalled phagocytosis and an accumulation of neurons with double strand DNA breaks, a marker of cell stress. Conversely, exogenous IFN-I was sufficient to drive neuronal engulfment by microglia and restrict the accumulation of damaged neurons. IFN-I deficient mice had excess excitatory neurons in the developing somatosensory cortex as well as tactile hypersensitivity to whisker stimulation. These data define a molecular mechanism through which microglia engulf neurons during a critical window of brain development. More broadly, they reveal key homeostatic roles of a canonical antiviral signaling pathway in brain development.

Effectiveness of nationwide programmatic testing and treatment for latent tuberculosis infection in migrants in England: a retrospective, population-based cohort study.

BACKGROUND: In low-incidence countries, tuberculosis mainly affects migrants, mostly resulting from reactivation of latent tuberculosis infection (LTBI) acquired in high-incidence countries before migration. A nationwide primary care-based LTBI testing and treatment programme for migrants from high-incidence countries was therefore established in high tuberculosis incidence areas in England. We aimed to assess the effectiveness of this programme. METHODS: We did a retrospective, population-based cohort study of migrants who registered in primary care between Jan 1, 2011, and Dec 31, 2018, in 55 high-burden areas with programmatic LTBI testing and treatment. Eligible individuals were aged 16-35 years, born in a high-incidence country, and had entered England in the past 5 years. Individuals who tested interferon-γ release assay (IGRA)-negative were advised about symptoms of tuberculosis, whereas those who tested IGRA-positive were clinically assessed to rule out active tuberculosis and offered preventive therapy. The primary outcome was incident tuberculosis notified to the national Enhanced Tuberculosis Surveillance system. FINDINGS: Our cohort comprised 368 097 eligible individuals who had registered in primary care, of whom 37 268 (10·1%) were tested by the programme. 1446 incident cases of tuberculosis were identified: 166 cases in individuals who had IGRA testing (incidence 204 cases [95% CI 176-238] per 100 000 person-years) and 1280 in individuals without IGRA testing (82 cases [77-86] per 100 000 person-years). Overall, in our primary analysis including all diagnosed tuberculosis cases, a time-varying association was identified between LTBI testing and treatment and lower risk of incident tuberculosis (hazard ratio [HR] 0·76 [95% CI 0·63-0·91]) when compared with no testing. In stratified analysis by follow-up period, the intervention was associated with higher risk of tuberculosis diagnosis during the first 6 months of follow-up (9·93 [7·63-12·9) and a lower risk after 6 months (0·57 [0·41-0·79]). IGRA-positive individuals had higher risk of tuberculosis diagnosis than IGRA-negative individuals (31·9 [20·4-49·8]). Of 37 268 migrants who were tested, 6640 (17·8%) were IGRA-positive, of whom 1740 (26·2%) started preventive treatment. LTBI treatment lowered the risk of tuberculosis: of 135 incident cases in the IGRA-positive cohort, seven cases were diagnosed in the treated group (1·87 cases [95% CI 0·89-3·93] per 1000 person-years) and 128 cases were diagnosed in the untreated group (10·9 cases [9·16-12·9] per 1000 person-years; HR 0·14 [95% CI 0·06-0·32]). INTERPRETATION: A low proportion of eligible migrants were tested by the programme and a small proportion of those testing positive started treatment. Despite this, programmatic LTBI testing and treatment of individuals migrating to a low-incidence region is effective at diagnosing active tuberculosis earlier and lowers the long-term risk of progression to tuberculosis. Increasing programme participation and treatment rates for those testing positive could substantially impact national tuberculosis incidence. FUNDING: National Institute for Health Research Health Protection Research Unit in Respiratory Infections.

Barriers and enablers to implementing tuberculosis control strategies in EU and European Economic Area countries: a systematic review.

Meeting the 2035 WHO targets of reducing tuberculosis incidence by 90% from 2015 levels requires the implementation of country-specific tuberculosis control strategies. This systematic review aims to identify factors that facilitate or impede the implementation of such strategies in EU and European Economic Area (EEA) settings. Focusing on providers of care, health system constraints, and social and political factors, this Review complements available evidence on the accessibility of tuberculosis services to recipients of care. Databases were searched for EU and EEA articles published between Jan 1, 1997, and Nov 6, 2020, that presented empirical data on tuberculosis policies, strategies, guidelines, or interventions. 2061 articles were screened and 65 were included. The most common barrier to tuberculosis control strategies described the divergence of health-care practices from guidelines, often related to inadequate knowledge or perceived usefulness of the guidelines by clinicians. The most commonly identified enabler to tuberculosis control strategies was the documented positive attitudes of health-care workers towards tuberculosis programmes. Divergence between clinical practice and guidelines was described in most EU and EEA settings, indicating the need for a focused review of guideline adherence. Strengths of this study involve its broad inclusion criteria and wide range of tuberculosis control strategies analysed.

Loss of Roundabout Guidance Receptor 2 (Robo2) in Podocytes Protects Adult Mice from Glomerular Injury by Maintaining Podocyte Foot Process Structure.

Roundabout guidance receptor 2 (ROBO2) plays an important role during early kidney development. ROBO2 is expressed in podocytes, inhibits nephrin-induced actin polymerization, down-regulates nonmuscle myosin IIA activity, and destabilizes kidney podocyte adhesion. However, the role of ROBO2 during kidney injury, particularly in mature podocytes, is not known. Herein, we report that loss of ROBO2 in podocytes [Robo2 conditional knockout (cKO) mouse] is protective from glomerular injuries. Ultrastructural analysis reveals that Robo2 cKO mice display less foot process effacement and better-preserved slit-diaphragm density compared with wild-type littermates injured by either protamine sulfate or nephrotoxic serum (NTS). The Robo2 cKO mice also develop less proteinuria after NTS injury. Further studies reveal that ROBO2 expression in podocytes is up-regulated after glomerular injury because its expression levels are higher in the glomeruli of NTS injured mice and passive Heymann membranous nephropathy rats. Moreover, the amount of ROBO2 in the glomeruli is also elevated in patients with membranous nephropathy. Finally, overexpression of ROBO2 in cultured mouse podocytes compromises cell adhesion. Taken together, these findings suggest that kidney injury increases glomerular ROBO2 expression that might compromise podocyte adhesion and, thus, loss of Robo2 in podocytes could protect from glomerular injury by enhancing podocyte adhesion that helps maintain foot process structure. Our findings also suggest that ROBO2 is a therapeutic target for podocyte injury and podocytopathy.

Developmental Apoptosis Promotes a Disease-Related Gene Signature and Independence from CSF1R Signaling in Retinal Microglia.

Microglia have important remodeling functions in neurodevelopment, aging, and disease, with evidence for molecular diversity. However, the signaling pathways and environmental cues that drive diverse states of microglia are incompletely understood. We profiled microglia of a discrete developing CNS region, the murine retina. We found distinct transcriptional signatures for retinal microglia across development and peak postnatal density of a population that resembles aging and disease-associated microglia (DAM) and CD11c+ microglia of developing white matter. While TREM2 signaling modulates the expression of select genes, the DAM-related signature is significantly reduced in retinas lacking Bax, a proapoptotic factor required for neuronal death. Furthermore, we found postnatal retinal microglia highly expressing CD11c are resistant to loss or inhibition of colony stimulating factor 1 receptor (CSF1R), while most microglia can be eliminated in Bax knockout retina. Thus, developmental apoptosis promotes a microglia gene signature linked to CSF1R independence that shares features with microglia in developing white matter and in disease.

Effectiveness of interventions for reducing TB incidence in countries with low TB incidence: a systematic review of reviews.

AIMS: What is the evidence base for the effectiveness of interventions to reduce tuberculosis (TB) incidence in countries which have low TB incidence? METHODS: We conducted a systematic review of interventions for TB control and prevention relevant to low TB incidence settings (<10 cases per 100 000 population). Our analysis was stratified according to "direct" or "indirect" effects on TB incidence. Review quality was assessed using AMSTAR2 criteria. We summarised the strength of review level evidence for interventions as "sufficient", "tentative", "insufficient" or "no" using a framework based on the consistency of evidence within and between reviews. RESULTS: We found sufficient review level evidence for direct effects on TB incidence/case prevention of vaccination and treatment of latent TB infection. We also found sufficient evidence of beneficial indirect effects attributable to drug susceptibility testing and adverse indirect effects (measured as sub-optimal treatment outcomes) in relation to use of standardised first-line drug regimens for isoniazid-resistant TB and intermittent dosing regimens. We found insufficient review level evidence for direct or indirect effects of interventions in other areas, including screening, adherence, multidrug-resistant TB, and healthcare-associated infection. DISCUSSION: Our review has shown a need for stronger evidence to support expert opinion and country experience when formulating TB control policy.

Complement Targets Newborn Retinal Ganglion Cells for Phagocytic Elimination by Microglia.

Microglia play important roles in shaping the developing CNS, and at early stages they have been proposed to regulate progenitor proliferation, differentiation, and neuronal survival. However, these studies reveal contradictory outcomes, highlighting the complexity of these cell-cell interactions. Here, we investigate microglia function during embryonic mouse retina development, where only microglia, progenitors, and neurons are present. In both sexes, we determine that microglia primarily interact with retinal neurons and find that depletion of microglia via conditional KO of the Csf1 receptor results in increased density of retinal ganglion cells (RGCs). Pharmacological inhibition of microglia also results in an increase in RGCs, with no effect on retinal progenitor proliferation, RGC genesis, or apoptosis. We show that microglia in the embryonic retina are enriched for phagocytic markers and observe engulfment of nonapoptotic Brn3-labeled RGCs. We investigate the molecular pathways that can mediate cell engulfment by microglia and find selective downregulation of complement pathway components with microglia inhibition, and further show that C1q protein marks a subset of RGCs in the embryonic retina. KO of complement receptor 3 (CR3; Itgam), which is only expressed by microglia, results in increased RGC density, similar to what we observed after depletion or inhibition of microglia. Thus, our data suggest that microglia regulate neuron elimination in the embryonic mouse retina by complement-mediated phagocytosis of non-apoptotic newborn RGCs.SIGNIFICANCE STATEMENT Microglia are emerging as active and important participants in regulating neuron number in development, during adult neurogenesis, and following stem cell therapies. However, their role in these contexts and the mechanisms involved are not fully defined. Using a well-characterized in vivo system, we provide evidence that microglia regulate neuronal elimination by complement-mediated engulfment of nonapoptotic neurons. This work provides a significant advancement of the field by defining in vivo molecular mechanisms for microglia-mediated cell elimination. Our data add to a growing body of evidence that microglia are essential for proper nervous system development. In addition, we elucidate microglia function in the developing retina, which may shed light on microglia involvement in the context of retinal injury and disease.

Developmental roles of microglia: A window into mechanisms of disease.

Microglia are engineers of the central nervous system (CNS) both in health and disease. In addition to the canonical immunological roles of clearing damaging entities and limiting the spread of toxicity and death, microglia remodel the CNS throughout life. While they have been extensively studied in disease and injury, due to their highly variable functions, their precise role in these contexts still remains uncertain. Over the past decade, we have greatly expanded our understanding of microglial function, including their essential homeostatic roles during development. Here, we review these developmental roles, identify parallels in disease, and speculate whether developmental mechanisms re-emerge in disease and injury. Developmental Dynamics 248:98-117, 2019. © 2018 Wiley Periodicals, Inc.

Tuberculosis in the European Union and European Economic Area: a survey of national tuberculosis programmes.

How many European Union (EU) and European Economic Area (EEA) countries have national tuberculosis (TB) control plans/strategies, and what are the priority actions/populations and barriers to implementation?In order to answer this question, a survey of EU/EEA national TB programme leads was undertaken.The response rate was 100% (31 countries). 55% of countries reported having a national TB strategy, all of which were in implementation; five countries were preparing a strategy. 74% had a defined organisational TB control structure with central coordination and 19% had a costed programme budget; few organisational structures included patient/civil society representation. The most frequently mentioned priority TB control actions were: reaching vulnerable population groups (80%), screening for active TB in high-risk groups (63%), implementing electronic registries (60%), contact tracing and outbreak investigation (60%), and tackling multidrug-resistant TB (60%). Undocumented migrants were the most commonly (46%) identified priority population. Perceived obstacles to implementation included barriers related to care recipients (lack of TB knowledge, treatment seeking/adherence), care providers (including need for specialist training of nurses and doctors) and health system constraints (funding, communication between healthcare and social care systems).This survey has provided an insight into TB control programmes across the EU/EEA that will inform the development of a TB strategy toolkit for member states.

Complement C3-Targeted Gene Therapy Restricts Onset and Progression of Neurodegeneration in Chronic Mouse Glaucoma.

Dysregulation of the complement system is implicated in neurodegeneration, including human and animal glaucoma. Optic nerve and retinal damage in glaucoma is preceded by local complement upregulation and activation, but whether targeting this early innate immune response could have therapeutic benefit remains undefined. Because complement signals through three pathways that intersect at complement C3 activation, here we targeted this step to restore complement balance in the glaucomatous retina and to determine its contribution to degeneration onset and/or progression. To achieve this, we combined adeno-associated virus retinal gene therapy with the targeted C3 inhibitor CR2-Crry. We show that intravitreal injection of AAV2.CR2-Crry produced sustained Crry overexpression in the retina and reduced deposition of the activation product complement C3d on retinal ganglion cells and the inner retina of DBA/2J mice. This resulted in neuroprotection of retinal ganglion cell axons and somata despite continued intraocular pressure elevation, suggesting a direct restriction of neurodegeneration onset and progression and significant delay to terminal disease stages. Our study uncovers a damaging effect of complement C3 or downstream complement activation in glaucoma, and it establishes AAV2.CR2-Crry as a viable therapeutic strategy to target pathogenic C3-mediated complement activation in the glaucomatous retina.

Reduction in tuberculosis incidence in the UK from 2011 to 2015: a population-based study.

BACKGROUND: Following nearly two decades of increasing tuberculosis in the UK, TB incidence decreased by 32% from 2011 to 2015. Explaining this reduction is crucial to informing ongoing TB control efforts. METHODS: We stratified TB cases notified in the UK and TB cases averted in the UK through pre-entry screening (PES) between 2011 and 2015 by country of birth and time since arrival. We used population estimates and migration data to establish denominators, and calculated incidence rate ratios (IRRs) between 2011 and 2015. We calculated the contribution of changing migrant population sizes, PES and changes in TB rates to the reduction in TB notifications. RESULTS: TB IRRs fell in all non-EU migrant and UK-born populations between 2011 and 2015 (0.61; 95% CI 0.59 to 0.64 and 0.78; 0.73 to 0.83 respectively), with the greatest decrease in recent non-EU migrants (0.54; 0.48 to 0.61). 61.9% of the reduction in TB notifications was attributable to decreases in TB rates, 33.4% to a fall in the number of recent/mid-term non-EU migrants and 11.4% to PES. A small increase in notifications in EU-born migrants offset the reduction by 6.6%. CONCLUSIONS: Large decreases in TB rates in almost all populations accounted for the majority of the reduction in TB notifications, providing evidence of the impact of recent interventions to improve UK TB control. The particularly large decrease in TB rates in recent non-EU migrants provides evidence of the effectiveness of screening interventions that target this population. These findings will inform ongoing improvements to TB control.

Immunoelectron Microscopy for Visualization of Nanoparticles.

Immunoelectron microscopy (IEM) on a solid phase such as a carbon film is a fast and powerful way to detect and visualize surface antigens on nanoparticles by using a transmission electron microscope (TEM). Nanoparticles, in particular ones for medical applications, are often modified on the surface with soft materials to make them more soluble, less toxic, or targetable to cancerous tumors. Imaging the soft material on the surface of solid nanoparticles by electron microscopy is often a challenge. IEM can overcome this issue in cases where antibodies to any of the surface material are available, which is often the case for proteins, but also for commonly used materials such as polyethylene glycol (PEG). This effective procedure has been used traditionally for viruses and macromolecules, but it can be directly applied to nanoparticles.

Tracking and responding to an outbreak of tuberculosis using MIRU-VNTR genotyping and whole genome sequencing as epidemiological tools.

Background: We describe an outbreak that contributed to a near doubling of the incidence of tuberculosis in Southampton, UK. We examine the importance of 24 locus mycobacterial interspersed repetitive unit variable number tandem repeat (MIRU-VNTR) genotyping in its identification and management and the role of whole genome sequencing (WGS) in tracing the spread of the strain. Methods: Outbreak cases were defined as those diagnosed between January and December 2011 with indistinguishable 24 locus-MIRU-VNTR genotypes or, cases linked epidemiologically. A cluster questionnaire was administered by TB nurses to identify contacts and social settings. Results: Overall, 25 patients fulfilled the case definition. No cases with this MIRU-VNTR genotype had been detected in the UK previously. Connections were found between all cases through household contacts or social venues including a football club, Internet cafe and barber's shop. Public health actions included extended contact tracing, venue screening and TB awareness-raising. The outbreak resulted in a high rate of transmission and high incidence of clinical disease among contacts. Conclusions: This outbreak illustrates the value of combining active case-finding with prospective MIRU-VNTR genotyping to identify settings to undertake public health action. In addition WGS revealed that the VNTR-defined cluster was a single outbreak and that active TB transmission not reactivation was responsible for this outbreak in non-UK born individuals.

Loss of Fractalkine Signaling Exacerbates Axon Transport Dysfunction in a Chronic Model of Glaucoma.

Neurodegeneration in glaucoma results in decline and loss of retinal ganglion cells (RGCs), and is associated with activation of myeloid cells such as microglia and macrophages. The chemokine fractalkine (FKN or Cx3cl1) mediates communication from neurons to myeloid cells. Signaling through its receptor Cx3cr1 has been implicated in multiple neurodegenerative diseases, but the effects on neuronal pathology are variable. Since it is unknown how FKN-mediated crosstalk influences RGC degeneration in glaucoma, we assessed this in a chronic mouse model, DBA/2J. We analyzed a DBA/2J substrain deficient in Cx3cr1, and compared compartmentalized RGC degeneration and myeloid cell responses to those in standard DBA/2J mice. We found that loss of FKN signaling exacerbates axon transport dysfunction, an early event in neurodegeneration, with a significant increase in RGCs with somal accumulation of the axonal protein phosphorylated neurofilament, and reduced retinal expression of genes involved in axon transport, Kif1b, and Atp8a2. There was no change in the loss of Brn3-positive RGCs, and no difference in the extent of damage to the proximal optic nerve, suggesting that the loss of fractalkine signaling primarily affects axon transport. Since Cx3cr1 is specifically expressed in myeloid cells, we assessed changes in retinal microglial number and activation, changes in gene expression, and the extent of macrophage infiltration. We found that loss of fractalkine signaling led to innate immune changes within the retina, including increased infiltration of peripheral macrophages and upregulated nitric oxide synthase-2 (Nos-2) expression in myeloid cells, which contributes to the production of NO and can promote axon transport deficits. In contrast, resident retinal microglia appeared unchanged either in number, morphology, or expression of the myeloid activation marker ionized calcium binding adaptor molecule 1 (Iba1). There was also no significant increase in the proinflammatory gene interleukin 1 beta (Il1ß). We conclude that loss of fractalkine signaling causes a selective worsening of axon transport dysfunction in RGCs, which is linked to enhanced Nos-2 expression in myeloid cells. Our findings suggest that distinct mechanisms may contribute to different aspects of RGC decline in glaucoma, with axonal transport selectively altered after loss of Cx3cr1 in microglia and/or macrophages.