African swine fever virus impairs porcine alveolar macrophages bactericidal function by disrupting lysosomal acidification and cathepsin activity
- 1State Key Laboratory of Veterinary Public Health Safety, College of Veterinary Medicine, China Agricultural University, Beijing, P.R. China
- 2Key Laboratory of Animal Epidemiology of Ministry of Agriculture and Rural Affairs, College of Veterinary Medicine, China Agricultural University, Beijing, P.R. China
Abstract
African swine fever virus (ASFV) is a devastating pathogen that poses a severe threat to the global swine industry. ASFV primarily targets the porcine monocyte-macrophage system, which is crucial for defending against bacterial infections via phagocytosis and subsequent intracellular degradation. Clinically, ASFV infection can be complicated by severe secondary bacterial infections. This creates a compelling paradox: while prior in vitro studies indicate that ASFV actually increases the phagocytic activity of porcine alveolar macrophages (PAMs), clinical observations frequently report severe secondary bacterial infections. This contradiction led us to hypothesize that the downstream intracellular bactericidal clearance might be compromised. Here, utilizing an in vitro co-infection model, it was demonstrated that ASFV significantly impairs the bactericidal capacity of PAMs against representative bacteria (Escherichia coli, Glaesserella parasuis, and Streptococcus suis), facilitating their intracellular survival and persistence. Although ASFV infection triggers massive reactive oxygen species (ROS) production, this oxidative stress remains functionally ineffective because phagolysosomal acidification and structural integrity are profoundly impaired. Mechanistically, at the late stage of infection, ASFV launches a multipronged assault on the endolysosomal network. Structurally, ASFV inhibits phagosomal and lysosomal acidification while inducing oxidative stress-driven severe lysosomal membrane permeabilization (LMP), leading to reduced phagolysosome volume and physical depletion of the lysosomal pool. Molecularly, ASFV impairs degradative capacity through the transcriptional suppression and blunted lysosomal enrichment of vacuolar (H+) ATPase (V-ATPase) subunits, alongside the disruption of lysosomal protease cathepsin D (CTSD) maturation. Furthermore, systematic screening identified six core candidate viral proteins, including CP530R, D129R, E183L, O174L, Q706L, and QP509R, that profoundly suppress both ATP6V0D and CTSK transcription, further exacerbating this functional impairment. Collectively, our in vitro findings reveal that ASFV dismantles host phagolysosomal acidification, thereby neutralizing the microbicidal potential of infected macrophages and potentially converting them into a permissive niche for secondary bacterial pathogens. These observations provide critical new mechanistic insights that may help explain ASFV-associated immune dysfunction at the cellular level. Author summary: African swine fever virus (ASFV) is a devastating pathogen for the global swine industry. ASFV primarily infects the porcine mononuclear phagocytes, whereas macrophages eliminate bacteria mainly through phagocytosis and bactericidal activity. Our previous in vitro studies have demonstrated that ASFV infection enhances the phagocytic capacity of PAMs. This observation appears paradoxical in light of field reports documenting increased secondary bacterial infections in ASFV-affected herds, and our present findings provide a mechanistic basis for reconciling these seemingly contradictory phenomena at the cellular level. Here, we demonstrate that ASFV significantly impairs the bactericidal capacity of PAMs, facilitating intracellular bacterial survival and delayed clearance. Strikingly, although ASFV infection triggers elevated ROS production, this oxidative burst is rendered functionally ineffective by the profound impairment of phagolysosomal acidification and structural collapse. Mechanistically, late-stage ASFV infection induces cytoplasmic alkalization, halts phagolysosomal acidification, and triggers severe lysosomal membrane permeabilization (LMP). This paralysis is driven by the transcriptional repression and impaired recruitment of V-ATPase to lysosomes upon bacterial challenge, the disrupted maturation of the lysosomal protease cathepsin D, and the targeted transcriptional repression of cathepsin K by specific viral proteins. Collectively, our findings reveal a novel immune suppression strategy whereby ASFV functionally cripples host phagolysosomal acidification and lysosomal protease activity. This provides critical new insights into virus-bacteria synergy and the pathogenesis of secondary infections during ASFV outbreaks.
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BibTeX
@article{xu2026african,
title = {{African swine fever virus impairs porcine alveolar macrophages bactericidal function by disrupting lysosomal acidification and cathepsin activity}},
author = {Zhen Xu and Fengyang Shi and Zhiyong Xiang and Runzhi Guo and Zhenyu Wen and Yajin Qu and Quanlin Li and Qiongqiong Zhou and Peng Gao and Yongning Zhang and Xinna Ge and Jun Han and Xin Guo and Lei Zhou and Hanchun Yang},
journal = {PLOS Pathogens},
year = {2026},
month = sep,
doi = {10.1371/journal.ppat.1014573},
url = {https://journals.plos.org/plospathogens/article?id=10.1371/journal.ppat.1014573},
note = {CC BY 4.0},
}
RIS
TY - JOUR
TI - African swine fever virus impairs porcine alveolar macrophages bactericidal function by disrupting lysosomal acidification and cathepsin activity
AU - Zhen Xu
AU - Fengyang Shi
AU - Zhiyong Xiang
AU - Runzhi Guo
AU - Zhenyu Wen
AU - Yajin Qu
AU - Quanlin Li
AU - Qiongqiong Zhou
AU - Peng Gao
AU - Yongning Zhang
AU - Xinna Ge
AU - Jun Han
AU - Xin Guo
AU - Lei Zhou
AU - Hanchun Yang
PY - 2026
DA - 2026/09/10
JO - PLOS Pathogens
DO - 10.1371/journal.ppat.1014573
UR - https://journals.plos.org/plospathogens/article?id=10.1371/journal.ppat.1014573
AB - African swine fever virus (ASFV) is a devastating pathogen that poses a severe threat to the global swine industry. ASFV primarily targets the porcine monocyte-macrophage system, which is crucial for defending against bacterial infections via phagocytosis and subsequent intracellular degradation. Clinically, ASFV infection can be complicated by severe secondary bacterial infections. This creates a compelling paradox: while prior in vitro studies indicate that ASFV actually increases the phagocytic activity of porcine alveolar macrophages (PAMs), clinical observations frequently report severe secondary bacterial infections. This contradiction led us to hypothesize that the downstream intracellular bactericidal clearance might be compromised. Here, utilizing an in vitro co-infection model, it was demonstrated that ASFV significantly impairs the bactericidal capacity of PAMs against representative bacteria (Escherichia coli, Glaesserella parasuis, and Streptococcus suis), facilitating their intracellular survival and persistence. Although ASFV infection triggers massive reactive oxygen species (ROS) production, this oxidative stress remains functionally ineffective because phagolysosomal acidification and structural integrity are profoundly impaired. Mechanistically, at the late stage of infection, ASFV launches a multipronged assault on the endolysosomal network. Structurally, ASFV inhibits phagosomal and lysosomal acidification while inducing oxidative stress-driven severe lysosomal membrane permeabilization (LMP), leading to reduced phagolysosome volume and physical depletion of the lysosomal pool. Molecularly, ASFV impairs degradative capacity through the transcriptional suppression and blunted lysosomal enrichment of vacuolar (H+) ATPase (V-ATPase) subunits, alongside the disruption of lysosomal protease cathepsin D (CTSD) maturation. Furthermore, systematic screening identified six core candidate viral proteins, including CP530R, D129R, E183L, O174L, Q706L, and QP509R, that profoundly suppress both ATP6V0D and CTSK transcription, further exacerbating this functional impairment. Collectively, our in vitro findings reveal that ASFV dismantles host phagolysosomal acidification, thereby neutralizing the microbicidal potential of infected macrophages and potentially converting them into a permissive niche for secondary bacterial pathogens. These observations provide critical new mechanistic insights that may help explain ASFV-associated immune dysfunction at the cellular level. Author summary: African swine fever virus (ASFV) is a devastating pathogen for the global swine industry. ASFV primarily infects the porcine mononuclear phagocytes, whereas macrophages eliminate bacteria mainly through phagocytosis and bactericidal activity. Our previous in vitro studies have demonstrated that ASFV infection enhances the phagocytic capacity of PAMs. This observation appears paradoxical in light of field reports documenting increased secondary bacterial infections in ASFV-affected herds, and our present findings provide a mechanistic basis for reconciling these seemingly contradictory phenomena at the cellular level. Here, we demonstrate that ASFV significantly impairs the bactericidal capacity of PAMs, facilitating intracellular bacterial survival and delayed clearance. Strikingly, although ASFV infection triggers elevated ROS production, this oxidative burst is rendered functionally ineffective by the profound impairment of phagolysosomal acidification and structural collapse. Mechanistically, late-stage ASFV infection induces cytoplasmic alkalization, halts phagolysosomal acidification, and triggers severe lysosomal membrane permeabilization (LMP). This paralysis is driven by the transcriptional repression and impaired recruitment of V-ATPase to lysosomes upon bacterial challenge, the disrupted maturation of the lysosomal protease cathepsin D, and the targeted transcriptional repression of cathepsin K by specific viral proteins. Collectively, our findings reveal a novel immune suppression strategy whereby ASFV functionally cripples host phagolysosomal acidification and lysosomal protease activity. This provides critical new insights into virus-bacteria synergy and the pathogenesis of secondary infections during ASFV outbreaks.
SN - 1553-7374
ER -