Recent studies have revealed important genetic mutations that affect neutrophilia, particularly in genes like AKT1, MAPK14, JAK1, and CD44. AKT1 acts as a key negative regulator of neutrophil recruitment and activation [15]. MAPK14, also known as p38 MAPK, drives cellular responses to stress and inflammation. JAK1 mediates signals from pro-inflammatory cytokines, which directly influence neutrophil growth and development. Additionally, CD44 is a cell surface glycoprotein that is crucial for neutrophil death and is linked to several inflammatory diseases [10]. These genetic findings not only improve our understanding of neutrophilia but also identify potential treatment targets for inflammatory and blood disorders.

Recent research has identified the S100A8/A9-NLRP3-IL-1β axis as a critical driver of neutrophilia and associated tissue damage in pathologies such as cardiovascular disease. The pathway operates through a sequential cascade: the damage-associated molecular patterns (DAMPs) S100A8/A9 activate the NLRP3 inflammasome, culminating in the caspase-1-dependent cleavage and secretion of IL-1β. This cytokine acts centrally to promote both the bone marrow production (granulopoiesis) and peripheral priming of neutrophils, exacerbating inflammation and driving tissue injury [11].

Therapeutically, targeting this axis offers a strategic approach. IL-1 receptor antagonism with agents such as anakinra has shown significant clinical benefit in mitigating mortality in severe hyperinflammatory states, including COVID-19-related acute respiratory distress syndrome (ARDS) [12, 13]. This is supported by a growing body of evidence demonstrating that by blocking the IL-1 receptor, anakinra effectively dampens the overwhelming 'cytokine storm’ that drives systemic inflammation, organ failure, and death in these critically ill patients [14]. Concurrently, novel pharmacologic inhibitors of the NLRP3 inflammasome present an upstream strategy to suppress detrimental inflammation without broadly compromising antimicrobial immunity.

Separately, emerging research highlights the gut microbiome as a critical systemic regulator of inflammation and immunity [15]. Gut microbiota-derived metabolites, such as short-chain fatty acids, have been demonstrated to modulate neutrophil maturation, recruitment, and effector functions. This independent axis of immune regulation unveils a novel therapeutic avenue. Strategies aimed at manipulating the gut microbiome—including probiotics, prebiotics, or fecal microbiota transplantation—are now being investigated for their potential to resolve chronic inflammation across a spectrum of diseases, representing a distinct frontier in immunomodulatory therapy [2, 3].

ORMDL sphingolipid biosynthesis regulator 3 (ORMDL3) is a gene that regulates sphingolipid metabolism, particularly influencing the sphingosine-1-phosphate (S1P) pathway. In respiratory diseases, uncontrolled ORMDL3-dependent sphingosine-1-phosphate (S1P) signalling drives harmful neutrophil movement in severe asthma. This makes S1P receptin modulators, including fingolimod derivatives, promising treatment options [16]. Similarly, in COVID-19, the activation of PFKFB3- a gene that encodes the enzyme 6-phosphofructo-2-kinase/fructose-2,6-biphosphatase 3 in neutrophils by SARS-CoV-2, worsens the unique form of cell death that is characterized by the release of decondensed chromatin and granular contents to the extracellular space called NETosis and cytokine storms. This suggests that metabolic inhibitors may be potential therapies [17].

Cytokine-targeted biologics are gaining significant popularity as precision tools in immunology. This is especially true for therapies targeting the IL-33 pathway, because emerging research shows IL-33 signaling can uniquely suppress neutrophilic inflammation—a key driver of severe, steroid-resistant disease—while simultaneously preserving or even promoting beneficial Type 2 (eosinophil-driven) immune responses, which are critical for parasite clearance and tissue repair [18]. The IL-17/22 pathway also plays a cooperative role in asthma. Additionally, G-CSF’s effects on kidney injury and the inhibition of PI3K by ginsenoside Rg3 in Chronic obstructive pulmonary disease (COPD) show how specific pathway changes can tackle extra-pulmonary neutrophilia [19]. The finding that Signal Transducer and Activator of Transcription 1 (STAT1) suppresses neutrophil recruitment during influenza-fungal co-infections, along with the issue of chemotherapy-induced “neutrophil resonance,” highlights the need for timely interventions.

Researchers are leveraging new mechanistic insights to develop targeted clinical applications. A primary strategy involves biomarker-driven patient stratification. For instance, patients most likely to respond to NLRP3 inflammasome inhibitors—which target a key multi-protein complex in innate immunity—could be identified by measuring circulating levels of IL-1β or S100A8/A9 heterodimers. This approach aims to maximize therapeutic effectiveness while minimizing side effects [11, 18].

Another promising avenue in immunomodulation exploits the intricate crosstalk between the host immune system and the microbiome. Pharmaceutical-grade derivatives of specific microbial metabolites, such as polysaccharide A (PSA) from the commensal bacterium Bacteroides fragilis, are being actively explored in preclinical and early clinical development. Their significant potential lies in their ability to precisely fine-tune dysregulated neutrophil responses—reducing destructive hyperinflammation in conditions like sepsis or autoimmune diseases—without inducing a state of generalized immunosuppression, thereby leaving critical host defense mechanisms intact [20].

Furthermore, dual-pathway targeting is emerging as a strategy for complex, treatment-resistant inflammatory conditions. For example, combining IL-17 blockade with S1P receptor modulators may yield superior outcomes in severe asthma [21].

Collectively, these advancements are foundational to precision medicine in inflammation, transforming neutrophilia from a passive diagnostic marker into a dynamic, therapeutically modifiable system.

Recent technological advancements are revolutionizing the study and management of neutrophilia. Cutting-edge techniques such as flow cytometry, combined with 5-ethynyl-2′-deoxyuridine (EdU) incorporation and advanced gating strategies, have enabled precise quantification and characterization of neutrophil populations in myocardial infarction models, shedding light on their recruitment mechanisms [22]. Meanwhile, bioinformatics tools are being leveraged to analyze gene expression data from microarray datasets, facilitating the identification of differentially expressed genes—such as AKT1 and CD44—and their associated pathways in neutrophilia [23]. Additionally, quantitative systems pharmacology (QSP) modeling is providing new insights into neutrophil dynamics during chemotherapy, allowing for optimized treatment regimens that mitigate neutropenia risks [24]. Together, these innovations are not only deepening our mechanistic understanding but also accelerating the development of novel biomarkers and targeted therapies.

Looking ahead, research into neutrophilia is poised to make significant strides across multiple fronts. The integration of genetic, microbiome, and cytokine profiling will enable true precision medicine approaches, allowing clinicians to tailor neutrophil-modulating therapies to individual patient biology. Metabolic interventions targeting pathways like 6-Phosphofructo-2-kinase/fructose-2,6-bisphosphatase 3 (PFKFB3) inhibition may prove particularly valuable for managing COVID-19-associated neutrophilia and its complications [25]. Simultaneously, engineered microbiome-derived therapeutics, including synthetic microbial metabolites, could offer novel ways to fine-tune neutrophil activity while avoiding broad immunosuppression.

These advances in understanding neutrophilic disorders naturally extend to their clinical counterpart - neutropenia. Just as we’re developing targeted strategies to suppress pathological neutrophilia, parallel innovations are emerging to address deficient neutrophil production and function. The same technologies enabling precise neutrophil modulation - from cytokine profiling to microbiome engineering - may be adapted to boost neutrophil counts in chemotherapy-induced or congenital neutropenias. Furthermore, the real-time monitoring tools being developed for neutropenia could be equally valuable for tracking neutrophil recovery in neutropenic patients. This bidirectional translation of research insights between neutrophilia and neutropenia highlights how advances in one area can inform therapeutic approaches in the other, creating a more comprehensive understanding of neutrophil biology and its clinical management.

Recent studies have significantly advanced our understanding of neutropenia by identifying diverse genetic mutations that contribute to its pathogenesis. For instance, two Ethiopian siblings initially misdiagnosed with xeroderma pigmentosum were found to carry a homozygous pathogenic variant in the USB1 gene (c.682C>T; p.Gln228*) and a novel heterozygous mutation in CSF3R (g.160C>T; p.His54Tyr), suggesting an atypical presentation of poikiloderma with neutropenia [26]. In severe congenital neutropenia (SCN), mutations such as ELANE p.Ala79del (c.234_236del) and p.Val197GlufsTer18 (c.589_590insAGGCCGGC) disrupt neutrophil elastase function, while a de novo SEC61A1 missense mutation (c.A275G; p.Q92R) further expands the genetic heterogeneity of SCN [27, 28]. Additional ELANE variants (e.g., F218L, R34W) impair enzyme activity, increasing infection susceptibility, whereas mutations in SRPRA and SRP19 highlight the critical role of the signal recognition particle (SRP) complex in neutrophil maturation [29, 30]. Similarly, CSF3R mutations (e.g., c.359G>A, p.G120D) compromise G-CSF receptor signaling, contributing to cyclic neutropenia, and the Wiskott-Aldrich syndrome protein mutations- *WASP-I292T* gain-of-function mutation demonstrates a distinct mechanism in X-linked neutropenia, supported by murine models [31, 32]. These findings underscore the genetic complexity of neutropenia and the need for ongoing refinement of diagnostic screening.

The disruption of neutrophil homeostasis by Bruton’s tyrosine kinase (BTK) inhibitors in non-malignant contexts involves multiple interconnected pathways, each offering specific therapeutic opportunities. BTK regulates granulopoiesis by modulating PI3K-AKT and MAPK signaling in myeloid progenitors; its inhibition arrests maturation at the myeloblast-promyelocyte stage, though this reversible defect suggests transient PI3K/AKT modulation could restore differentiation [33]. Concurrently, BTK inhibition impairs G-CSF receptor signaling (reduced STAT5 phosphorylation) while enhancing CXCR4-mediated marrow retention, explaining why plerixafor outperforms G-CSF monotherapy in mitigating neutropenia [34]. Off-target effects further exacerbate the condition, as ibrutinib’s suppression of TEC kinase reduces GM-CSF/IL-3 production, though newer agents like acalabrutinib (with lower TEC affinity) exhibit milder myelosuppression [33]. Within the bone marrow niche, BTK maintains progenitor support via NF-κB-dependent stromal cytokine production and β1-integrin anchoring; its inhibition leads to hypocellularity, which experimental cytokine supplementation can reverse, suggesting thrombopoietin agonists (e.g., eltrombopag) might stabilize the niche [34]. Finally, BTK sustains circulating neutrophils by stabilizing Mcl-1 and suppressing caspases via PI3K-AKT/NF-κB. Its inhibition shortens neutrophil lifespan from 6–8 to under 4 h through BAD/caspase-9 activation, implying that AKT inhibitors (e.g., miransertib) could prolong survival [33].

Future therapeutic strategies should prioritize biomarker-guided approaches (e.g., monitoring CXCR4/G-CSF levels and pAKT/pSTAT3 signaling to personalize plerixafor or cytokine therapy), kinase-selective optimization (e.g., BTK/TEC-bispecific inhibitors), niche-targeted interventions (e.g., stromal IL-3/GM-CSF nanoparticles), and apoptosis modulation (e.g., Mcl-1 stabilizers like sabutoclax).

Recent innovations in neutropenia diagnostics combine genomic, proteomic, and non-invasive technologies to enhance precision and patient convenience. Whole-genome sequencing (WGS) and mass spectrometry have identified distinct proteomic signatures in SCN, while the ASPEN study’s hierarchical statistical framework (Cochran-Mantel-Haenszel test) has improved the rigor of clinical trial analyses [31, 34, 35]. The Point Check device exemplifies progress in patient-friendly monitoring, using optical imaging to quantify neutrophils transcutaneously, eliminating the need for frequent blood draws [36].

Recent advances have identified several pathogenic mutations contributing to eosinophilia through distinct molecular mechanisms. The JAK2_ex12InDel mutation causes a 4-amino acid deletion with variable 1-amino acid insertion in the JH2 domain, disrupting autoinhibition and leading to constitutive STAT5/ERK activation through IL-3R/IL-5R independent of ligand binding [37]. This results in uncontrolled eosinophil production and survival, often accompanied by erythrocytosis, suggesting phenotypic overlap with polycythemia vera [36]. Another significant finding is the JAK1 R629_S632delinsA mutation in the pseudokinase domain, which confers growth factor independence through persistent JAK-STAT activation and demonstrates responsiveness to ruxolitinib in clonal eosinophilia [38].

The TrkA F921 mutation in the ATP-binding pocket alters eosinophil trafficking by enhancing spreading while inhibiting eotaxin-1-mediated migration, presenting a novel therapeutic target for allergic asthma [39]. In primary immunodeficiencies, the STAT3 c.1293A>T missense mutation disrupts immune regulation, leading to AD-HIES characterized by elevated IgE and eosinophilia [40]. IL5RA variants in eosinophilic esophagitis (EoE) enhance IL-5 receptor signaling, driving tissue inflammation through exaggerated eosinophilic responses [41–43]. These findings collectively reveal the genetic complexity underlying eosinophilic disorders.

The pathogenesis involves dysregulated signaling pathways that promote eosinophil differentiation, survival, and tissue infiltration. Constitutive JAK-STAT activation [37, 38] bypasses normal cytokine regulation, while TrkA F921 alters chemotactic responses to eotaxin-1 [39]. In AD-HIES, defective STAT3 signaling [40] promotes Th2 polarization and IL-5-driven eosinophilopoiesis, whereas IL5RA mutations [41–43] hypersensitize eosinophils to IL-5 stimulation. These mechanisms demonstrate how diverse genetic lesions converge on common inflammatory pathways.

Recent molecular insights have revolutionized therapeutic approaches for eosinophilic disorders through targeted interventions. JAK inhibitors such as ruxolitinib demonstrate significant efficacy in JAK1/2-mutant eosinophilia by suppressing constitutive signaling pathway activation [38]. For allergic inflammation, emerging TrkA-targeted therapies show promise in normalizing pathological eosinophil migration patterns while preserving physiological immune functions [44]. Monoclonal antibodies against the IL-5 pathway, particularly mepolizumab, achieve dramatic eosinophil reduction in IL5RA-associated eosinophilic esophagitis by interrupting this critical cytokine-receptor axis [41–43]. In the context of immune dysregulation, novel STAT3 modulators offer potential for correcting the underlying Th2 skewing characteristic of AD-HIES while maintaining protective immunity [40]. These precision medicine approaches collectively highlight the essential role of comprehensive genetic and molecular profiling in guiding therapeutic decision-making for eosinophilic disorders, moving beyond empirical treatment toward mechanism-based interventions tailored to each patient’s specific pathophysiology.

Modern genomic technologies have revolutionized eosinophilia evaluation, with whole exome sequencing (WES) uncovering pathogenic STAT6 mutations in pediatric allergic cases [45, 46] and next-generation sequencing (NGS) identifying disease-associated STAT1 variants in familial eosinophilic esophagitis (EoE) [47]. The integration of fluorescence in situ hybridization (FISH) with NGS has proven particularly valuable for characterizing PDGFRB rearrangements and detecting somatic mutations in genes like TET2 and DNMT3A in myeloid-associated eosinophilia [48, 49]. Complementary functional approaches, including immunofluorescence microscopy and Western blot analysis, have further elucidated the protein-level consequences of mutations such as TrkA F921 on eosinophil behavior and signaling pathways [39]. Together, these advanced techniques provide a multidimensional assessment of eosinophilic disorders, enabling clinicians to establish precise molecular diagnoses and tailor therapeutic strategies to individual patients’ genetic profiles.

While eosinophilia mechanisms are increasingly defined, eosinopenia pathogenesis remains less understood. Preliminary evidence suggests IL-5 signaling defects, glucocorticoid excess, or CEP112 mutations may impair eosinopoiesis. Emerging single-cell technologies may reveal shared regulatory mechanisms between these opposing conditions, potentially identifying novel therapeutic targets for eosinophil homeostasis disorders.

Eosinopenia (eosinophil counts <100/μL) has emerged as a significant clinical biomarker, particularly in infectious and respiratory diseases. In COVID-19, persistent eosinopenia shows strong prognostic value, present in 86% of non-survivors compared to only 50% of survivors [50], with evidence suggesting type 1 interferon-mediated suppression of eosinopoiesis may contribute to this association [51]. The biomarker demonstrates particular clinical utility in acute exacerbations of COPD (AECOPD), where its combination with lymphocytopenia shows 100% sensitivity for predicting mortality [52]. Furthermore, eosinopenia proves valuable for infection detection in patients receiving IL-6 pathway antagonists like tocilizumab, where traditional inflammatory markers may be suppressed [53]. These findings collectively establish eosinopenia as an accessible and clinically relevant indicator of disease severity across multiple pathological contexts.

The pathophysiology of eosinopenia involves complex regulatory mechanisms, best characterized in glucocorticoid-induced cases. Research using rhesus macaque models - which closely mirror human responses unlike rodent models - reveals that glucocorticoids rapidly upregulate CXCR4 on eosinophils within 1–2 h, facilitating their migration to CXCL12-rich bone marrow niches [54]. This mechanism was conclusively demonstrated through innovative ⁸⁹Zr-oxine PET imaging techniques, with CXCR4 blockade by plerixafor completely abolishing the glucocorticoid-induced eosinopenic effect [55]. The specificity of this response highlights both the importance of model selection in eosinophil research and the potential for targeted therapeutic interventions modulating this trafficking pathway.

The clinical management of eosinopenia-related conditions benefits from these mechanistic insights, particularly in monitoring infections in immunocompromised patients, where eosinophil thresholds below 0.05 G/L serve as reliable indicators [53]. Diagnostic capabilities have been significantly enhanced by technological advances, including ⁸⁹Zr-oxine PET imaging for real-time eosinophil tracking and immunomagnetic isolation techniques that permit high-purity eosinophil studies [54]. These developments not only improve our understanding of eosinophil dynamics but also open possibilities for targeted therapies, such as CXCR4 modulation to manage glucocorticoid side effects while maintaining therapeutic efficacy [55].

As our understanding of eosinophil regulation advances, parallel investigations into basophil disorders - encompassing both basophilia and basopenia - become increasingly pertinent. The technological and mechanistic insights gained from eosinopenia research, particularly regarding granulocyte trafficking and biomarker applications, may prove equally valuable in elucidating basophil pathophysiology in allergic, infectious, and inflammatory conditions.