Targeting S100A8 mitigates pathogenic neutrophil-driven tissue injury in bacterial epididymo-orchitis.

Bacterial epididymo-orchitis, primarily driven by uropathogenic Escherichia coli (UPEC), is a major cause of inflammatory testicular injury and male infertility. While our previous study indicates that neutrophils are rapidly recruited to the immune-privileged testis to contain the infection, their excessive activation can paradoxically exacerbate tissue destruction. However, the specific cellular states and molecular mediators driving this injurious inflammatory response remain poorly defined. To address this gap, we utilized single-cell transcriptomics in a murine orchitis model to map the dynamic remodeling of the testicular neutrophil compartment. We identified a dominant pathogenic subpopulation (Cluster 0) that rapidly expands during acute infection and is characterized by robust S100a8 expression (accompanied by concomitant induction of its heterodimeric partner, S100a9). Flow cytometric and spatial analyses confirmed the marked accumulation of CD11b+Ly6G+S100A8+ neutrophils within damaged reproductive niches. Notably, pharmacological inhibition of the S100A8/S100A9 complex with paquinimod reduced this pathogenic neutrophil infiltration and preserved testicular architecture. Together, these findings identify S100A8 as a key marker and candidate contributor to neutrophil-mediated tissue injury, and suggest that this axis warrants further investigation as a targeted immunomodulatory strategy that may help preserve fertility during bacterial infections.