Oral Presentation 33rd ASM of the Australian & New Zealand Bone & Mineral Society 2023

Introduction: Osteomyelitis (OM) is an infection of the bone, a systemic infection leading to multiple bone tissue dysfunction, coupled with drug resistance, bloodstream infection, and limited clinical treatment options. Symptoms may include pain in a specific bone with overlying redness, fever, and weakness. Objectives: This work aims to further investigate the new interplay between bacterial exocrine regulatory protein and host immune cells in the chronic osteomyelitis microenvironment. Whether interfering with related regulatory signaling pathways can reverse the inflammatory disorder of bone immune cells. Methods: In-depth analysis of single-cell sequencing results in patients for potential immunodeficiency factors. Analysis of key proteins enriched by host cells and key pathways using proteomics. Cell models and animal models validate the pathological effects of bacterial heat shock protein (DnaK) on T cells, MAITs, macrophages, and osteoclasts. Results: We identified that S. maltophilia-DnaK was enriched in immunodeficient T cells. The activation of the JAK2/STAT1 axis initiated the exhaustion of T cells. Patients with Gram-negative bacterial infections exhibited deficiencies in MAITs, which correspond to IFN-γ. Cellular and animal experiments confirmed that DnaK could facilitate MAIT depletion and M1 polarization of macrophages. Additionally, Fludarabine mitigated M1 polarization in mice. Interestingly, DnaK also repressed osteoclastogenesis of macrophages stimulated by RANKL. Conclusions: DnaK prompts the activation of the JAK2/STAT1 axis in T cells and the M1 polarization of macrophages. Targeting the DnaK’s crosstalk can be a potentially effective approach for treating the inflammatory disorder in the chronic osteomyelitis microenvironment.