Qingfei Paidu decoction, a compound Chinese herbal medicine, protects against post-influenza bacterial infection by inhibiting the formation of neutrophil extracellular traps and cytokine storm.

OBJECTIVE: Post-influenza bacterial infection is associated with higher severity and mortality rates. Qingfei Paidu decoction (QFPDD) has demonstrated efficacy as an anti-inflammatory therapeutic agent specifically for influenza. However, its role in bacterial secondary infection remains unclear. This study aimed to investigate the protective effects and underlying mechanisms of QFPDD in a mouse model of post-influenza bacterial infection.

METHODS: A mouse model of post-influenza bacterial infection was established to evaluate the therapeutic effects of QFPDD. QFPDD was administered prior to the full establishment of secondary bacterial infection. Body weight, body temperature, lung indexes and pulmonary bacterial load were evaluated by lung weighing and colony counting of lung tissue homogenates. Single-cell ribonucleic acid sequencing (scRNA-seq) was performed to characterize immune cell populations and cytokine expression levels in lung tissues. Neutrophil activation, neutrophil extracellular trap (NET) formation and coagulation-related markers were examined using molecular and biochemical approaches. In vitro, pam3cys-ser-lys4 (Pam3CSK4)-stimulated macrophages were used to assess cytokine production, while the expression of phagocytic receptors was evaluated in macrophages and neutrophils following Pam3CSK4 or heat-killed Staphylococcus aureus stimulation. In addition, phorbol 12-myristate 13-acetate (PMA)-stimulated neutrophils were utilized to assess the production of reactive oxygen species (ROS) and the activation of signaling pathways.

RESULTS: QFPDD prevented body weight loss, reduced lung indexes, decreased lung bacterial load and alleviated hypothermia in secondary infected mice. ScRNA-seq analysis revealed decreased cytokine scores in the lungs following QFPDD treatment, with neutrophils exhibiting the highest cytokine scores among the 18 identified cell populations. QFPDD downregulated inflammatory mediators in neutrophils. Furthermore, QFPDD reduced the expression of xanthine oxidase, myeloperoxidase, citrullinated histone H3, and peptidyl arginine deiminase 4, accompanied by decreased S100 calcium-binding protein A8 and S100 calcium-binding protein A9 levels, suggesting that QFPDD can be associated with the reduced formation of NETs. QFPDD also decreased platelet activation and hypercoagulation markers. In vitro, QFPDD inhibited cytokine and chemokine production in macrophages and suppressed ROS generation and extracellular signal-regulated protein kinase phosphorylation in neutrophils. In addition, QFPDD significantly enhanced the expression of phagocytic receptors in macrophages and neutrophils.

CONCLUSION: QFPDD confers protection against post-influenza bacterial infection by inhibiting the formation of NETs and cytokine storm, highlighting its potential as a candidate for further investigation in the prevention and treatment of this condition. Please cite this article as: Mu JW, Cheng T, Hu L, Lei B, Ma YH, Cui Y, Peng YC, Huang WB, Ge YW, Ho LP, Zheng YJ. Qingfei Paidu decoction, a compound Chinese herbal medicine, protects against post-influenza bacterial infection by inhibiting the formation of neutrophil extracellular traps and cytokine storm. J Integr Med. 2026; 24(5):769-784.