Spatial analysis reveals the cellular microenvironments and mechanisms of inflammation and kidney injury in acute interstitial nephritis.

Acute interstitial nephritis (AIN) causes 15-20% of all acute kidney injury cases but lacks effective therapies beyond corticosteroids. Using high-resolution imaging mass cytometry and single-cell spatial transcriptomics to analyze human kidney biopsies with AIN, non-immunologic acute tubular injury (ATI), and reference tissue, the CXCL9-CXCR3 axis was identified as the defining immunologic signature of AIN, with 44-fold higher predicted CXCL9-CXCR3 interactions than ATI, creating homotypic inflammatory T cell amplification networks concentrated in lymphoid aggregates. C3AR1 + immune cells were enriched in peritubular neighborhoods of complement 3-expressing injured tubule cells, predominantly VCAM1 + injured proximal tubules, linking tubular injury to immune activation in AIN. Nicotinamide phosphoribosyltransferase ( NAMPT ) was the strongest predictor of VCAM1 + tubular microenvironments, with expression by both injured tubules and surrounding immune cells coordinating metabolic-inflammatory niches. These findings reveal distinct molecular circuits underlying AIN pathogenesis and identify potential therapeutic targets for improving clinical management and preventing progression to chronic kidney disease.