Fumarate hydratase (FH) has been shown to regulate mitochondrial RNA (mtRNA) release in lipopolysaccharide (LPS)-activated macrophages. In the cytosol, mtRNA activates the nucleic acid-sensing pattern recognition receptors RIG-I, MDA5 and TLR7 inducing IFN-β production. However, the mechanism of mtRNA release is still unclear. Here, we have investigated the role of Sorting Nexin 9 (SNX9) in this process. Silencing SNX9 blocked both the increase in cytosolic mtRNA and IFN-β production in both prolonged LPS stimulation and acute FH inhibition. Mechanistically, FH inhibition drives SNX9 mitochondrial localization 60 minutes after LPS stimulation where it interacts with TMEM11, a mitochondrial protein involved in mitochondrial dynamics. These results provide evidence for a role for SNX9 in the release of mtRNA in response to FH targeting leading to the induction of the anti-viral and immunomodulatory cytokine IFN-β in response to LPS.

BACKGROUND:Both low-grade systemic inflammation and acute inflammatory events may contribute to Alzheimer Disease (AD) progression. However, studies examining the prognostic utility of systemic inflammatory biomarkers in AD, and how systemic inflammatory events may contribute to clinical trajectories in AD, have yielded conflicting results. METHODS:We quantified plasma cytokines/chemokines in 333 individuals with mild-moderate AD at baseline, 12 and 18 months alongside baseline neurodegenerative biomarkers. AD severity was assessed using the Alzheimer Disease Assessment Scale (ADAS-Cog), Clinical Dementia Rating Scale (CDR-Sb) and Disability Assessment for Dementia (DAD). FINDINGS:Systemic inflammatory biomarkers were primarily associated with age/socio-demographic characteristics, remained strikingly stable over time, and were not associated with AD progression. Rather, higher baseline plasma p-tau217 was associated with greater yearly progression on both the ADAS-Cog (β: 2.82; 95% CI: 1.12, 4.52; nominal p = 0.001) and DAD (β: -2.34; 95% CI: -3.86, -0.82; nominal p = 0.003). Higher baseline GFAP was also associated with subsequent decline on both the CDR-Sb (β: 1.02; 95% CI: 0.38, 1.67; nominal p = 0.002) and DAD (β: 1.91; 95% CI: -3.45, -0.37; nominal p = 0.02). Experiencing one or more episodes of delirium was associated with accelerated decline on the CDR-Sb at 18-months (β: 2.63; 95% CI: 1.55, 3.71; adjusted p < 0.001). INTERPRETATION:Biomarkers of neuroinflammation (GFAP), neurodegeneration (p-tau217) and incident delirium, rather than systemic inflammatory biomarkers, were associated with clinically-significant decline in mild-moderate AD. FUNDING:European Commission (FP7 grant; 279093); Meath Foundation (MFRG 121/2021); Wellcome Trust (227946/Z/23/Z & 203930/B/16/Z); Health Research Board (203930/B/16/Z; ECSA-2024-003).

Autoantibodies neutralizing type-I interferons (AAN-I-IFNs) emerge as global, common, and strong determinants of a growing number of severe viral diseases. We report that AAN-I-IFNs+ patients with life-threatening COVID-19 pneumonia harbor circulating type-I IFN-specific B cells indistinguishable from patients bearing T cell tolerance defects of genetic origin. This autoimmune response mobilizes a highly diverse and stable circulating B cell response that is detected prior to severe viral infection and acquires high affinity and neutralization potential to type-I IFNs through extended somatic hypermutation. X-ray crystallography and AlphaFold3 structural analysis of hundreds of patient-derived monoclonal antibodies reveals the extended breadth of this response, targeting three major B cell epitopes covering all facets of type-I IFNs. These findings support a model in which a germinal-center-derived memory B cell response directed against type-I IFNs is established before severe viral infection, providing a core mechanism linking T cell tolerance defect to pathogenic AAN-I-IFNs underlying severe viral diseases.

[This corrects the article DOI: 10.1371/journal.pone.0309964.].

Chronic spontaneous urticaria and atopic dermatitis (AD) are chronic skin disorders characterized by itch. Although mast cells play an integral role in the pathogenesis of chronic spontaneous urticaria, their role in AD is unclear, having a contributory role in a disease largely driven by T helper 2 polarization. Despite this, the role of mast cells in AD is important, given their release of proinflammatory mediators. Recently, myeloid and mast cell progenitors were identified as potential biomarkers for treatment response in chronic spontaneous urticaria. These Lin-CD117+CD34+FceRI+ cells appear to have increased egress from the bone marrow in atopy. We measured Lin-CD117+CD34+FceRI+ cells in the peripheral blood of 10 individuals with AD and 10 healthy controls. Flow cytometry revealed a significant increase in myeloid progenitors in participants with AD (P = .0067). Total serum IgE levels did not correlate with myeloid progenitors. To our knowledge, examination of this cell type in AD is previously unreported. Our findings suggest increased progenitor egress from the bone marrow in these patients and a possible role for myeloid progenitors in disease pathogenesis.

Novel prognostic biomarkers are urgently needed in older adults with Alzheimer Disease (AD). Peripheral inflammation, systemic inflammatory events (SIEs) and delirium are increasingly recognised as AD risk factors, but their impact on progression in established AD and temporal relationships with AD progression remains unclear. Further, whether SIEs, adverse events and delirium interact with peripheral inflammation to accelerate AD is unknown. We analysed >1,000 plasma/cerebrospinal fluid samples from 333 patients with mild to moderate dementia due to AD with 18-months of follow-up. Ten cytokines/chemokines (IFN-γ, IL-6, IL-10, IL-12p70, IL-17A, TNF-α, Eotaxin, IP-10, MCP-1, MIP-1β) were quantified at baseline, 12, and 18-months using ultra-sensitive immunoassays. Baseline neurodegenerative biomarkers (p-tau217, p-tau181, t-tau, Neurofilament Light [NfL], Glial Fibrillary Acidic Protein [GFAP]) were measured using validated immunoassays. Clinical progression was assessed using Clinical Dementia Rating Scale (CDR-Sb). Results of linear and logistic regression models are reported as Beta Coefficients (B) and Odds Ratios (OR), respectively, with 95% Confidence Intervals and p-values and adjustment for important clinical confounders. Baseline peripheral inflammatory biomarkers (particularly IL-6 and IP-10) correlated significantly with age and sociodemographic factors but not AD severity. Peripheral inflammatory biomarkers remained remarkably stable over 18-months despite clinical-significant decline. Conversely, plasma biomarkers of AD pathophysiology (p-tau217) and neuro-inflammation (GFAP) at baseline strongly predicted accelerated AD progression (p-tau217: B:0.54, 0.18-1.08, p=0.02; GFAP: B:0.53, 0.18-0.90, p=0.002). Single (OR:2.63, 1.55-3.71, p<0.001) or multiple episodes of delirium (OR:3.45, 1.77-5.13, p<0.001), but not SIEs or adverse events, predicted greater progression on the CDR-Sb. Biomarkers specific to AD pathology (p-tau217, GFAP) rather than peripheral inflammation had robust prognostic value in established AD. Delirium was consistently associated with clinically-meaningful decline, highlighting the importance of delirium prevention efforts in older adults with AD. Our findings add strong evidence supporting the prognostic utility of p-tau217 and GFAP in older adults with established AD.

Background The ABO blood group system is associated with differential susceptibility to thrombotic vascular diseases. ABO is also known to be a strong trans-protein quantitative trait locus for plasma proteins involved in cell adhesion and hemostasis.Study Design and Method To further investigate these associations, we integrated epigenomic, genomic, and proteomic data from the Milieu Int & eacute;rieur cohort. We used the rs8176719 SNP to classify donors as either type O or non-O, and used linear models to compare levels of 229 plasma proteins in 400 donors, including age, sex, cytomegalovirus serostatus, and secretor status as covariates.Results We observed increased levels of soluble E-selectin and decreased levels of von Willebrand Factor (vWF) in O donors compared with non-O donors. By performing an epigenome-wide association study, we identified 23 differentially methylated CpG sites between blood types, which were all located in the ABO gene. Notably, CpG sites in the ABO promoter region of type O donors were less methylated than those of the non-O donors. Using mediation analysis, we found that these differences in DNA methylation partially explained the effects of blood group on differential E-selectin and vWF plasma levels.Discussion We find differentially methylated CpG sites between blood types and provide new evidence that ABO blood group status affects circulating levels of specific proteins.

Evidence increasingly supports the “infectious hypothesis” of Alzheimer Disease (AD) in older adults, proposing that common pathogens—particularly human herpesviruses—increase one's risk of AD. However, most studies have used medical records and clinically-diagnosed infections to test this association. To obtain a direct measure of viral exposure history, we developed a novel multiplex sero-assay enabling simultaneous measurement of antibodies to a broad variety of common infections and applied it to several unique clinical cohorts to interrogate the infectious hypothesis of AD. Using nearly 6,000 samples from three studies (TUDA, TIMC-BRAiN, NILVAD), plasma IgG to 50 pathogens was measured via a multiplex bead-based assay. Associations were examined in the community-based TUDA cohort and further explored in clinical cohorts (TIMC-BRAiN, NILVAD) using paired plasma/cerebrospinal fluid (CSF) samples and high-sensitivity biomarkers of inflammation and neurodegeneration. Linear regression results are presented as Beta Coefficients (B), 95% Confidence Intervals, and p-values with adjustment for important clinical covariates. In TUDA (n=4,796, age: 73.7±8.17 years, 67.2% female), Herpes Simplex Virus 1 (HSV1) seropositivity was significantly associated with poorer total RBANS scores (B: -3.78, 95%CI: -5.50 to -2.07, p<0.001) and poorer performance on all RBANS domains. Cytomegalovirus (CMV) seropositivity was significantly associated with poorer total RBANS performance (B: -1.38, 95%CI: -2.23 to -0.52, p=0.002). In NILVAD, CMV seropositivity was associated with greater baseline dementia severity (B: 1.47, 95%CI: 0.58 to 2.36, p=0.001 on CDR-Sb). In clinical cohorts (TIMC-BRAiN, NILVAD), pathogen seropositivity was not associated with AD biomarkers or AD clinical progression over 18-months. Across all three cohorts, herpesvirus seropositivity was consistently associated with elevated systemic inflammatory markers (IL-6, TNF-α). Herpesvirus exposure (HSV1, CMV) was robustly associated with poorer cognitive performance, potentially mediated by non-specific systemic inflammatory effects. However, direct involvement of HSV1 or CMV in AD pathogenesis or progression was not supported by the current analysis.

Chronic spontaneous urticaria (CSU) is a skin disorder characterised by recurrent hives and swellings that has a profound effect upon quality of life. Current guidelines for the management of CSU outline sequential use of standard dosing nonsedating H1 antihistamines, fourfold dose antihistamines and the anti-IgE monoclonal antibody omalizumab. A proportion of patients will have partial response or no response to omalizumab despite uptitration of dose. Evidence suggests that nonresponders may represent a specific endotype of Type IIb autoimmune CSU and respond better to ciclosporin, a fourth line off-licence treatment. Accurate and timely classification of CSU by endotype may enable personalised medicine for patients. Current attempts to classify CSU are based on distinct autoallergic and autoimmune pathways towards mast cell activation; Type I autoallergic urticaria as evidenced by IgE autoantibodies initiating FcεR1 crosslinking and Type IIb autoimmune urticaria as evidenced by IgG autoantibodies initiating FcεR1 crosslinking. However, recent data have demonstrated that the distinction between CSU endotypes is more nuanced, with overlap between categories whereby patients with Type IIb autoimmune CSU have been found to have coexistent IgE autoantibodies. A cohort of patients do not meet criteria for either endotype. Furthermore, there is recognition that laboratory parameters currently used to stratify patients are not widely available, hampering their practical use. This review seeks to summarise data on biomarkers associated with treatment response in CSU. While previous literature has focussed upon treatment response to antihistamines, our emphasis is on predicting treatment response to third and fourth-line treatments, with further reference to emerging treatments that do not yet form part of guidelines for management of CSU. Understanding factors that influence clinical response to all agents is particularly important as treatment options for CSU rapidly expand. In the following sections, we will evaluate the biochemical and clinical parameters that have been explored in these patients as well as their potential utility in routine clinical practice.

Purpose Evolution-informed therapies exploit evolutionary consequences of drug resistance to inhibit treatment resistance and prolong time to progression. One strategy, termed an evolutionary double-bind, uses an initial therapy to elicit a specific adaptive response by cancer cells, which is then selectively targeted by a follow-on therapy. Although the concept of an evolutionary double-bind has long been hypothesized in cancer, it has not been measured. Here, to our knowledge, we present the first example of a quantifiable double-bind: radiation therapy (RT) with natural killer (NK) cells. RT induces lethal double-strand DNA breaks, but cancer cells adapt. Although this increases resistance to DNA-damaging agents, it also enhances expression of NK cell ligands creating an obvious choice for a double-bind strategy. Methods and Materials We investigated this potential evolutionary double-bind through in vitro studies and evolution-based mathematical models. Using multiple prostate cancer cell lines, we evaluated surface and soluble NK ligand expression following RT. In vitro competition experiments were performed with an isogenic radiation-resistant cell line model. We introduced a two-population Lotka-Volterra competition model, consisting of radiation-sensitive and radiation-resistant populations modeling intrinsic growth rates with fixed carrying capacity and inter-specific competition terms. Results Alterations in NK cell ligands resulted in a twofold increase in sensitivity to NK cell-mediated killing with selective targeting of RT-resistant cells. These dynamics were framed mathematically to quantify the double bind. RT alone slowed overall growth but strongly selected for RT-resistant cells. NK cell therapy alone suppressed the RT-resistant population, but with a surviving population of radiation-sensitive cells. Model simulation predicted that optimal tumor control would be achieved through initial RT followed by NK cells. Subsequent experiments confirmed the model prediction. Conclusions We conclude that RT and NK cell-based immunotherapy produce an evolutionary double-bind. This multidimensional approach addresses the immediate challenge of treatment resistance and lays the groundwork for the development of personalized treatment regimens tailored to the evolving dynamics of individual tumors. Significance Clinical experience demonstrates that prostate cancer has a remarkable capacity to evolve resistance to all currently available treatments resulting in progression and, ultimately, patient death. Resistance mechanisms often come at a fitness cost placing cells in a bind when competing with surrounding cells. A carefully chosen secondary drug can introduce a double-bind targeting the adaptive resistance mechanism. This manuscript provides the first direct experimental evidence quantifying an “evolutionary double-bind’ in prostate cancer supporting the combination of DNA-damaging agents and NK cell-based immunotherapy in evolutionarily guided treatment designs. Our work is mathematically novel in that it extends Evolutionary Game Theory models and establishes an experimental-mathematical framework to quantify genuine evolutionary double binds applicable across cancer types and treatment modalities.

Background:Postacute sequelae of SARS-CoV-2 infection, also known as long COVID (LC), is a complex and heterogenous condition affecting millions worldwide with a poorly understood underlying pathology. Although metabolic dysregulations have been described in LC, it remains unclear whether circulating immune cells exhibit immunometabolic alterations. Methods:We conducted a detailed clinical, immunologic, and mitochondrial analysis on 27 patients with LC and 27 who recovered from COVID-19 and were healthy. Symptom burden and severity were assessed and quantified via a digital platform with the modified COVID-19 Yorkshire Rehabilitation Scale. Mitochondrial function of circulating immune cell populations (lymphocytes and monocytes) was analyzed by measuring mitochondrial mass and mitochondrial membrane potential. Production of 11 cytokines after whole blood stimulation with bacterial and viral agonists was measured by multiplex immunoassay. Relationships between mitochondrial and immune parameters with LC symptoms were investigated. Results:Patients with LC exhibited significant symptom burden, with worsening across all symptom domains as compared with their health state before SARS-CoV-2 infection. They also had a decreased mitochondrial membrane potential of CD56bright natural killer cells, particularly in patients experiencing dizziness, whereas reduced mitochondrial membrane potential in CD4+ lymphocytes was found in patients with worsening breathlessness. Upon LPS stimulation, patients with LC demonstrated significantly lower IFN-γ production. In response to viral ligand R848, impaired IFN-β and IL-10 responses were associated with worsening cough and executive functions. Conclusions:Symptom severity in LC is associated with immune cell mitochondrial dysfunction and altered cytokine responses, highlighting potential disease biomarkers and targets for future therapeutic strategies.

Individuals with low socioeconomic status (SES) are at greater risk of contracting and developing severe disease compared with people with higher SES. Age, sex, host genetics, smoking and cytomegalovirus (CMV) serostatus are known to have a major impact on human immune responses and thus susceptibility to infection. However, the impact of SES on immune variability is not well understood or explored. Here, we used data from the Milieu Intérieur project, a study of 1000 healthy volunteers with extensive demographic and biological data, to examine the effect of SES on immune variability. We developed an Elo-rating system using socioeconomic features such as education, income and home ownership status to objectively rank SES in the 1000 donors. We observed sex-specific SES associations, such as females with a low SES having a significantly higher frequency of CMV seropositivity compared with females with high SES, and males with a low SES having a significantly higher frequency of active smoking compared with males with a high SES. Using random forest models, we identified specific immune genes which were significantly associated with SES in both baseline and immune challenge conditions. Interestingly, many of the SES associations were sex stimuli specific, highlighting the complexity of these interactions. Our study provides a new way of computing SES in human populations that can help identify novel SES associations and reinforces biological evidence for SES-dependent susceptibility to infection. This should serve as a basis for further understanding the molecular mechanisms behind SES effects on immune responses and ultimately disease.

PROBLEM:The interleukin-17 (IL-17) family includes pro-inflammatory cytokines IL-17A-F with important roles in mucosal defence, barrier integrity and tissue regeneration. IL-17A can be dysregulated in fertility complications, including pre-eclampsia, endometriosis and miscarriage. Because mammalian subclasses (eutherian, metatherian, and prototherian) have different related reproductive strategies, IL-17 genes and proteins were investigated in the three mammalian classes to explore their involvement in female fertility. METHOD OF STUDY:Gene and protein sequences for IL-17s are found in eutherian, metatherian and prototherian mammals. Through synteny and multiple sequence protein alignment, the relationships among mammalian IL-17s were inferred. Publicly available datasets of early pregnancy stages and female fertility in therian mammals were collected and analysed to retrieve information on IL-17 expression. RESULTS:Synteny mapping and phylogenetic analyses allowed the classification of mammalian IL-17 family orthologs of human IL-17. Despite differences in their primary amino acid sequence, metatherian and prototherian IL-17s share the same tertiary structure as human IL-17s, suggesting similar functions. The analysis of available datasets for female fertility in therian mammals shows up-regulation of IL-17A and IL-17D during placentation. IL-17B and IL-17D are also found to be over-expressed in human fertility complication datasets, such as endometriosis or recurrent implantation failure. CONCLUSIONS:The conservation of the IL-17 gene and protein across mammals suggests similar functions in all the analysed species. Despite significant differences, the upregulation of IL-17 expression is associated with the establishment of pregnancy in eutherian and metatherian mammals. The dysregulation of IL-17s in human reproductive disorders suggests them as a potential therapeutic target.

Healthcare workers (HCWs) are at increased risk of SARS-CoV-2 infection. Despite widespread vaccination, some HCWs develop frequent symptomatic infection. We hypothesised that HCWs with frequent symptomatic COVID-19 have impaired T and B cell mediated immunity to SARS-CoV-2. Vaccinated HCWs with no prior COVID infection (n = 9), asymptomatic recent infection (n = 10), and frequent recent infection (n = 15) were recruited from a longitudinal HCW cohort study. Whole blood stimulation with SARS-CoV-2 variants (Wuhan, B.1.617, BA.2, BA.2.75, BA.4/5, XBB.1.5, BQ.1.1) was performed, with IFNγ and IL-2 responses, total IgG produced, and anti-Spike antibody neutralising capacity measured. Frequent infections had similar IFNγ and IL-2 responses to the never infected group, with significantly higher responses in the asymptomatic group. The frequent cohort had higher IgG responses to Delta and BA.4/5 and higher neutralising capacity against Omicron variants. An immune signature of blunted IL-2 and IFNγ in frequent infections may identify HCWs at increased risk of further infection.

Abstract Background There has been unprecedented progress in the development of blood-based biomarkers (BBMs such as p-tau217 to detect Alzheimer Disease (AD) pathology – characterised by the accumulation of Amyloid-Beta (Aβ) and hyper-phosphorylated tau (T). However, BBM performance in “real-world” memory clinic contexts remains unclear. Methods Using high-sensitivity immunoassays, plasma p-tau217 was assessed in 554 participants. Two cohorts were studied: (i) a memory clinic validation cohort of 108 older adults (69 ± 6.5 years; 54.6% female) with early cognitive symptoms and paired plasma/cerebrospinal fluid (CSF) at time of diagnostic Lumbar Puncture (LP) and (ii) a broader replication cohort of 446 individuals ranging from cognitively-unimpaired middle-aged adults to older adults with established AD with 18-month follow-up. Plasma P-tau217 performance was examined against clinically established CSF Aβ+/T+ cut-offs using Area-Under the Curve (AUC) analysis. Plasma cut-offs were optimised vs CSF based on maximal Youden index. Results In the memory clinic cohort, plasma p-tau217 exhibited excellent performance for the detection of Aβ pathology (AUC: 0.91, 0.86-0.97). Plasma p-tau217 was nearly 4-fold higher in Aβ+ (13.89; 7.36-19.0pg/mL) vs Aβ- (3.72; 2.80-4.09pg/mL, U = 230, p<0.001) participants. Plasma p-tau217 was superior in the identification of Aβ vs T pathology (p<0.05, DeLong Test) and outperformed p-tau181 and other BBMs(all p<0.05, DeLong Test). In the replication cohort, plasma p-tau217 maintained >90% accuracy for clinical AD and was significantly associated with clinically meaningful cognitive decline over 18 months (Odds Ratio 1.40; 1.06-1.85, p=0.02). In the initial memory clinic cohort, application of plasma p-tau217 as a diagnostic test would have reduced the need for LPs by over half (56.5%). Conclusion Plasma p-217 demonstrates excellent diagnostic and prognostic performance in older adults with AD, representing an amyloid-responsive measure which also predicts meaningful cognitive decline in established AD. Incorporation of plasma p-tau217 in memory clinic settings may substantially reduce the need for over half of diagnostic LPs.

Bovine respiratory disease (BRD) is a leading cause of mortality and compromised welfare in bovines. It is a polymicrobial syndrome resulting from a complex interplay of viral and bacterial pathogens with environmental factors. Despite the availability of vaccines, incidence and severity in young calves remains unabated. A more precise analysis of host innate immune responses during infection will identify improved diagnostic and prognostic biomarkers for early intervention and targeted treatments to prevent severe disease and loss of production efficiency. Here, we investigate hematological and innate immune responses using standardized ex-vivo whole blood assays in calves diagnosed with BRD. A total of 65 calves were recruited for this study, all between 2-8 weeks of age with 28 diagnosed with BRD by a thoracic ultrasonography score (TUS) and 19 by Wisconsin health score (WHS) and all data compared to 22 healthy controls from the same 9 study farms. Haematology revealed circulating immune cell populations were similar in both TUS positive and WHS positive calves compared to healthy controls. Gene expression analysis of 48 innate immune signalling genes in whole blood stimulated with TLR ligands was completed in a subset of calves. TLR1/2 stimulation with Pam3CSK4 showed a decreased pattern of expression in IL-1 and inflammasome related genes in addition to chemokine genes in calves with BRD. In response to TLR ligands LPS, Pam3CSK4 and R848, protein analysis of supernatant collected from all calves with BRD revealed significantly increased IL-6, but not IL-1 beta or IL-8, compared to healthy controls. This hyper-induction of IL-6 was observed most significantly in response to TLR1/2 stimulation in TUS positive calves. ROC analysis identified this induced IL-6 response to TLR1/2 stimulation as a potential diagnostic for BRD with a 74% true positive and 5% false positive detection rate for an IL-6 concentration >1780pg/mL. Overall, these results show altered immune responses specifically upon TLR1/2 activation is associated with BRD pathology which may contribute to disease progression. We have also identified induced IL-6 as a potentially informative biomarker for improved early intervention strategies for BRD.

BACKGROUND:Chronic spontaneous urticaria (CSU) is a common, debilitating skin disorder characterized by recurring episodes of raised, itchy and sometimes painful wheals lasting longer than 6 weeks. CSU is mediated by mast cells which are absent from peripheral blood. However, lineage-CD34hiCD117int/hiFcεRI+ cells in blood have previously been shown to represent a mast cell precursor. METHODS:We enumerated FcεRI-, FcεRI+ and FcεRIhi lineage-CD34+CD117+ cells using flow cytometry in blood of patients with CSU (n = 55), including 12 patients receiving omalizumab and 43 not receiving omalizumab (n = 43). Twenty-two control samples were studied. Disease control and patient response to omalizumab was evaluated using the urticaria control test. We performed single-cell RNA sequencing (scRNA-Seq) on lineage-CD34hiCD117hi blood cells from a subset of patients with CSU (n = 8) and healthy controls (n = 4). RESULTS:CSU patients had more lineage-CD34+CD117+FcεRI+ blood cells than controls. Lineage-CD34+CD117+FcεRI+ cells were significantly higher in patients with CSU who had an objective clinical response to omalizumab when compared to patients who had poor disease control 90 days after initiation of omalizumab. scRNA-Seq revealed that lineage-CD34+CD117+FcεRI+ cells contained both lymphoid and myeloid progenitor lineages, with omalizumab responsive patients having proportionally more myeloid progenitors. The myeloid progenitor lineage contained small numbers of true mast cell precursors along with more immature FcεRI- and FcεRI+ myeloid progenitors. CONCLUSION:Increased blood CD34+CD117+FcεRI+ cells may reflect enhanced bone marrow egress in the setting of CSU. High expression of these cells strongly predicts better clinical responses to the anti-IgE therapy, omalizumab.