The Brucella effector protein BtpB facilitates STAT3 activation to regulate polarization in macrophages during infection
Abstract
Brucella is a Gram-negative facultative intracellular pathogen that causes widespread zoonotic infections. Macrophages are crucial immune and antigen-presenting cells that differentiate into proinflammatory M1-type or anti-inflammatory M2-type cells in different microenvironments. The BtpB protein of Brucella is a type IV secretion system effector protein that modulates host inflammatory responses by inhibiting Toll-like receptor signaling and controlling dendritic cell activation. A high expression of intracellular proinflammatory factors is induced in B. suis deficient in BtpB (B. suis mutant strain ΔbtpB). However, the role of BtpB in macrophage polarization triggered by Brucella infection is uncertain. In this study, RAW264.7 macrophages were utilized as a model to investigate the impact of BtpB on macrophage polarization. The cells were infected with wild-type B. suis strain S2, B. suis mutant strain ΔbtpB, or the B. suis complemented strain C-ΔbtpB followed by flow cytometry, reverse transcription quantitative PCR (RT-qPCR), western blotting, immunohistochemistry, and metabolic detection analyses. The expression of BtpB suppressed M1 polarization and promoted M2 macrophage polarization. Moreover, BtpB upregulated the expression of signal transducer and activator of transcription 3 (STAT3) in host cells. Inhibition of STAT3 promoted the expression of nitric oxide synthase (NOS2) in cells infected with either B. suis or C-ΔbtpB, with no observable differences compared to cells infected with ΔbtpB. Conversely, STAT3 overexpression resulted in a downregulation of NOS2 levels in both wild-type and mutant cells. These findings were corroborated by messenger RNA (mRNA) assay and enzyme-linked immunosorbent assay (ELISA) that confirmed the regulatory role of STAT3 in modulating NOS2 expression. Additionally, intracellular proliferation assays under STAT3-modulated conditions indicated that STAT3 suppresses replication of Brucella. In conclusion, the results demonstrate that BtpB inhibits M1 polarization in macrophages by regulating STAT3 expression which provides a strong foundation for improved understanding of Brucella infection mechanisms.Graphical Abstract
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BibTeX
@article{yuan2026brucella,
title = {{The Brucella effector protein BtpB facilitates STAT3 activation to regulate polarization in macrophages during infection}},
author = {Ye Yuan and Minghui Wang and Mingyue Hao and Jialu Chen and Xiaofang Liu and Yuanhao Yang and Yimeng Cui and Shengnan Li and Wei Liu and Dong Zhou and Wei Liu and Yaping Jin and Aihua Wang},
journal = {Veterinary Research},
year = {2026},
month = sep,
doi = {10.1186/s13567-026-01833-8},
url = {https://hal.science/hal-05737988v1},
note = {CC BY 4.0},
}
RIS
TY - JOUR
TI - The Brucella effector protein BtpB facilitates STAT3 activation to regulate polarization in macrophages during infection
AU - Ye Yuan
AU - Minghui Wang
AU - Mingyue Hao
AU - Jialu Chen
AU - Xiaofang Liu
AU - Yuanhao Yang
AU - Yimeng Cui
AU - Shengnan Li
AU - Wei Liu
AU - Dong Zhou
AU - Wei Liu
AU - Yaping Jin
AU - Aihua Wang
PY - 2026
DA - 2026/09/03
JO - Veterinary Research
DO - 10.1186/s13567-026-01833-8
UR - https://hal.science/hal-05737988v1
AB - Brucella is a Gram-negative facultative intracellular pathogen that causes widespread zoonotic infections. Macrophages are crucial immune and antigen-presenting cells that differentiate into proinflammatory M1-type or anti-inflammatory M2-type cells in different microenvironments. The BtpB protein of Brucella is a type IV secretion system effector protein that modulates host inflammatory responses by inhibiting Toll-like receptor signaling and controlling dendritic cell activation. A high expression of intracellular proinflammatory factors is induced in B. suis deficient in BtpB (B. suis mutant strain ΔbtpB). However, the role of BtpB in macrophage polarization triggered by Brucella infection is uncertain. In this study, RAW264.7 macrophages were utilized as a model to investigate the impact of BtpB on macrophage polarization. The cells were infected with wild-type B. suis strain S2, B. suis mutant strain ΔbtpB, or the B. suis complemented strain C-ΔbtpB followed by flow cytometry, reverse transcription quantitative PCR (RT-qPCR), western blotting, immunohistochemistry, and metabolic detection analyses. The expression of BtpB suppressed M1 polarization and promoted M2 macrophage polarization. Moreover, BtpB upregulated the expression of signal transducer and activator of transcription 3 (STAT3) in host cells. Inhibition of STAT3 promoted the expression of nitric oxide synthase (NOS2) in cells infected with either B. suis or C-ΔbtpB, with no observable differences compared to cells infected with ΔbtpB. Conversely, STAT3 overexpression resulted in a downregulation of NOS2 levels in both wild-type and mutant cells. These findings were corroborated by messenger RNA (mRNA) assay and enzyme-linked immunosorbent assay (ELISA) that confirmed the regulatory role of STAT3 in modulating NOS2 expression. Additionally, intracellular proliferation assays under STAT3-modulated conditions indicated that STAT3 suppresses replication of Brucella. In conclusion, the results demonstrate that BtpB inhibits M1 polarization in macrophages by regulating STAT3 expression which provides a strong foundation for improved understanding of Brucella infection mechanisms.Graphical Abstract
SN - 0928-4249
SN - 1297-9716
ER -