Neutrophil Reprogramming Fuels Immunosuppression in Staphylococcus aureus Biofilm Infection 2256977

Abstract

Neurosurgical procedures such as craniotomies carry up to a 15% infection risk, predominantly due to Staphylococcus aureus (S. aureus) biofilms. These biofilms resist antibiotics and promote immune suppression, enabling chronic infection. Granulocytic myeloid-derived suppressor cells (G-MDSCs) emerge as key mediators of this immunosuppression, but the mechanisms driving their development, presumably from neutrophils, remain poorly defined. We exposed bone marrow-derived neutrophils to S. aureus biofilm and analyzed phenotypic and functional changes via flow cytometry, RNA- sequencing, and T cell suppression assays. Genetic knockout models lacking Toll-like receptor 2 (TLR2) or MyD88 were used to delineate host signaling pathways. Additionally, we screened the S. aureus Nebraska Transposon Mutant Library (NTML) to identify bacterial factors responsible for neutrophil reprogramming. Exposure to S. aureus biofilm transformed neutrophils into G-MDSC-like cells, exhibiting elevated CD11b, CD14, and PD-L1 expression, reduced bactericidal capacity, and suppression of T cell proliferation. TLR2-deficient neutrophils showed markedly reduced acquisition of these traits, while MyD88 deletion completely prevented the shift, implicating MyD88-dependent pathways. NTML screening identified specific bacterial TLR2 ligands as essential for driving this reprogramming. Our findings reveal that S. aureus biofilms exploit TLR2-MyD88 signaling to reprogram neutrophils into immunosuppressive G-MDSC-like cells. This host-pathogen interaction underlies biofilm persistence and highlights both bacterial-derived TLR2 ligands and host TLR2 signaling as promising therapeutic targets to restore antimicrobial immunity in neurosurgical infections. CHRI Mini grant Microbial, Parasitic, and Fungal Immunology (MPF)