Prior work in Lupus Nephritis has shown that immune cell infiltration, especially that of monocytes, is associated with pathologic tissue remodeling and declining renal function. A deeper understanding of infiltrating monocytes could yield more accurate interpretations of histopathologic lesions, better disease predictors, and new therapeutic concepts. Newer technologies offer a promising path toward this goal. Single cell-RNA sequencing (scRNA-seq) enables the molecular classification of cell states based on the expression of thousands of genes, and multiplex-immunofluorescent imaging enables precise spatial localization of these cell states in the context of diseased tissue. Groundwork to merge these technologies derives from our work with the Accelerating Medicines Partnership (AMP) consortium.
In our recent work, scRNA-seq of lupus nephritis tissue identified 21 immune cell types enriched in diseased compared to healthy kidneys, including 3 monocyte cell states that may represent differing levels of differentiation. Leveraging scRNA-seq data, we developed panels based on the molecular classification of 3 monocyte cell states for staining human tissue. We applied multiplex-immunofluorescent imaging to map each monocyte state in kidney biopsies from 10 patients presenting with class IV lupus nephritis undergoing their first renal biopsy. While this approach validates monocytes identified by scRNA-seq, it also reveals that monocyte states preferentially localize to different compartments in the kidney, including the glomerulus and space between kidney tubules. Additional genomic analysis of monocytes suggests that each state executes different stages of the removal of dead cell debris from kidney tissue. Together, these results suggest that monocyte states are highly organized in lupus nephritis tissue and may carry out specific functions in distinct kidney compartments.
While prior work has shown monocyte infiltration per se correlates with renal function, we are working to understand the significance of monocyte organization in human lupus nephritis tissue. The patient cohort has been expanded to examine the spatial relationships of monocyte states to tissue lesions in the major histologic classes of lupus nephritis, and efforts are underway to determine what factors from tissue drive monocyte differentiation. Through careful molecular and spatial analyses of tissue, coupled with and mechanistic studies, our goal is to elucidate the clinical significance and biological principles driving monocyte organization in human lupus nephritis.