In the complex battlefield of infectious diseases, inflammation serves as both a shield and a sword. It is an essential component of the immune response, enabling the body to contain and eradicate invading pathogens. Yet, when inflammation spirals out of control, it transforms from protector to perpetrator, driving tissue damage and chronic disease. This paradox is exquisitely demonstrated during infections with Mycobacterium tuberculosis (Mtb), the causative agent of tuberculosis (TB), where immune responses dominated by neutrophils, a subset of white blood cells, often correlate with worsened disease outcomes. Despite their frontline role in defense, neutrophils in tuberculosis can paradoxically exacerbate lung pathology and inflammation. Recent groundbreaking research has now unveiled a critical molecular mechanism within neutrophils that determines the fine balance between protective immunity and pathological inflammation in TB.
The study, led by Kinsella et al. and published in Nature Microbiology, delves into the role of the autophagy-related protein ATG5 in modulating neutrophil responses during Mtb infection in mice. While ATG5 is traditionally recognized for its key role in autophagy — the cellular recycling pathway crucial for clearing damaged organelles and intracellular bacteria — this research uncovers an autophagy-independent function of ATG5 in neutrophils. Specifically, the researchers demonstrated that ATG5 acts as a critical suppressor of type I interferon (IFN)-mediated neutrophil effector functions, which if unchecked, potentiate inflammation and tissue damage during TB.
Neutrophils are renowned for their rapid recruitment to sites of infection, where they unleash a barrage of antimicrobial weapons. One pivotal effector mechanism is the release of neutrophil extracellular traps (NETs) — web-like chromatin structures laden with antimicrobial proteins that can ensnare and kill pathogens. However, excessive NETosis, the process of NET release, has been implicated in tissue injury and exacerbation of disease in various inflammatory disorders. A central discovery from Kinsella and colleagues’ work is that ATG5 deficiency in neutrophils leads to hyperactivation of a type I IFN-driven pathway that triggers overproduction of NETs during Mtb infection.
By employing sophisticated genetic mouse models — notably Atg5^fl/fl-LysM-Cre mice in which ATG5 is specifically deleted in myeloid cells including neutrophils — the researchers demonstrated a marked increase in early susceptibility to Mtb infection compared to control animals. This susceptibility was closely tied to dysregulated neutrophil responses, characterized by heightened release of NETs mediated through increased activity of peptidylarginine deiminase 4 (PAD4). PAD4 is an enzyme responsible for histone citrullination, a critical step in chromatin decondensation essential for NET formation. Their data revealed that in the absence of ATG5, type I IFN signaling upregulated PAD4-mediated histone citrullination, fueling excessive NET release.
The consequences of this dysregulation extend beyond NETosis. The study also elucidated that ATG5 mitigates neutrophil chemotaxis and swarming — collective migration of neutrophils to infection foci — by suppressing excessive secretion of the chemokine CXCL2, which is inducible by type I IFNs. This dual control by ATG5 serves to temper the amplitude of neutrophil infiltration and activation during the early phase of Mtb infection, thus protecting host tissues from collateral damage. The investigators used a combination of in vivo infection models and in vitro systems to validate these findings, confirming the autophagy-independent role of ATG5 in calibrating the type I IFN neutrophil axis.
Type I interferons, including IFN-α and IFN-β, are central antiviral cytokines that orchestrate complex immune responses. However, their role in bacterial diseases such as TB has been controversial and context-dependent. Elevated type I IFN signatures have been correlated with poor disease prognosis in TB patients, often linked to increased inflammation and immune evasion by the pathogen. The current study provides mechanistic insights into how type I IFNs can drive pathological neutrophil activation via PAD4 and NETosis, a process normally restrained by ATG5. This knowledge enhances our understanding of the dual-edged nature of type I IFN signaling during bacterial infections.
Furthermore, the findings have pragmatic implications for host-directed therapy—a therapeutic approach that aims to modulate the host immune response instead of directly targeting the pathogen. Since excessive neutrophil-mediated inflammation contributes to TB pathology, selectively augmenting the function of ATG5 or mimicking its regulatory effects could offer new avenues to limit immunopathology while preserving antimicrobial defense. Targeting the PAD4-NET pathway or CXCL2-mediated neutrophil recruitment also emerges as a viable strategy to quell damaging inflammation in TB.
Notably, this research underscores the importance of cell-type specific functions of autophagy proteins beyond classical autophagy. ATG5 exemplifies a multifunctional regulator that integrates signals from innate immune pathways to fine-tune neutrophil effector responses. This highlights the complexity of immune regulation at the molecular level and invites further investigation into ATG5’s role in other infectious and inflammatory diseases driven by neutrophils.
In the experimental design, the use of LysM-Cre recombinase allowed for precise deletion of ATG5 in myeloid lineage cells, ensuring that observed phenotypes were attributable to neutrophil dysfunction. The researchers complemented genetic models with functional assays for NET formation, histone citrullination, chemokine secretion, and neutrophil swarming behavior. The robust connection between increased PAD4 activity and NET release in ATG5-deficient neutrophils was corroborated with molecular markers, solidifying the link between ATG5 and suppression of pathological neutrophil activation.
These findings also bring to light the multifaceted consequences of type I IFN signaling during TB. While type I IFNs play protective antiviral roles, their aberrant activation during Mtb infection skews neutrophil function toward damaging hyperinflammation. ATG5 acts as an essential brake, preventing this immune circuit from tipping toward disease exacerbation. This nuanced regulation may explain some of the contradictory clinical observations regarding type I IFN’s impact on TB progression.
Moreover, the study raises intriguing questions about how ATG5 intersects with other signaling pathways in neutrophils and whether its modulation could influence chronic inflammation and fibrosis seen in TB and other lung diseases. Delineating the crosstalk between autophagy-related proteins and immune signaling networks presents fertile ground for future research that may extend beyond infectious disease paradigms.
Given the global burden of tuberculosis, which remains a leading cause of morbidity and mortality worldwide, advancing our understanding of immune regulation at the cellular and molecular level is paramount. Studies like this shed light on fundamental processes governing neutrophil behavior and provide a foundation for the rational design of therapies aimed at enhancing host resilience without exacerbating tissue injury. Such host-directed strategies are particularly appealing in the era of rising antibiotic resistance, where augmenting the body’s intrinsic defenses could complement or circumvent traditional antimicrobial treatments.
In summary, the work by Kinsella et al. identifies ATG5 as a master regulator of neutrophil effector functions modulated by type I interferons during Mtb infection. By restraining PAD4-driven histone citrullination and NET release, and by dampening CXCL2-mediated neutrophil swarming, ATG5 ensures balanced neutrophil activity that limits immunopathology and controls infection. This autophagy-independent function of ATG5 expands the paradigm of immune regulation and opens new avenues for targeted interventions to improve outcomes in tuberculosis and potentially other neutrophil-associated inflammatory diseases.
As tuberculosis remains a global health threat, the implications of this research are profound. Potential therapies derived from this mechanistic insight could transform how clinicians approach the delicate management of inflammation in infectious diseases. Modulating ATG5 pathways or their downstream effectors may enable the development of novel treatments that prevent the damaging hyperinflammatory responses characteristic of severe TB, ultimately reducing morbidity and mortality.
The unveiling of ATG5’s dual role exemplifies how advances in molecular immunology continue to unravel the intricate choreography of host-pathogen interactions and inflammatory regulation. With further validation and translation into human studies, targeting the ATG5-neutrophil axis might soon become a cornerstone of host-directed immunotherapies designed to tame inflammation without compromising microbial control.
Subject of Research: Regulation of neutrophil effector functions by ATG5 during Mycobacterium tuberculosis infection mediated via type I interferon signaling pathways.
Article Title: ATG5 suppresses type I IFN-dependent neutrophil effector functions during Mycobacterium tuberculosis infection in mice.
Article References:
Kinsella, R.L., Sur Chowdhury, C., Smirnov, A. et al. ATG5 suppresses type I IFN-dependent neutrophil effector functions during Mycobacterium tuberculosis infection in mice. Nat Microbiol (2025). https://doi.org/10.1038/s41564-025-01988-8
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