Deep profiling of lupus nephritis kidneys reveals dynamic changes in myeloid cells associated with disease progression

Objectives Lupus nephritis (LN) is a common, potentially fatal manifestation of systemic lupus erythematosus. We aimed to gain new insights into the immune responses underlying LN and their relation to the histologic heterogeneity observed in this disease, focusing on myeloid cells. Methods We used single-cell RNA-sequencing (scRNA-seq) data of dissociated kidney samples from 156 patients with LN and 30 healthy individuals. We applied spatial transcriptomics (ST), utilising a gene panel designed to capture all myeloid subsets identified in the scRNA-seq data, to profile kidney samples acquired from 6 patients with LN and 2 controls. Results We generated a catalogue of the myeloid subsets found in LN kidneys. Our analyses indicated that an increase in irreversible tissue damage, as measured by the National Institutes of Health chronicity index (CI), is associated with a gradual switch of the local immune response from one dominated by monocytes and macrophages to one featuring expanded CD4 T, GZMK + CD8 T, B, and dendritic cells, with a parallel decrease in the interferon response. In proliferative/mixed LN only, the degree of active inflammation correlates with the expansion of disease-specific macrophage (DMac) subsets, which later contract as the CI increases. Trajectory analysis of the scRNA-seq data suggested that DMacs arise from both infiltrating monocytes and tissue-resident macrophages; this was supported by the ST data, as well as cell cultures. DMacs are implied to interact with parietal epithelial cells, promoting the development of glomerulosclerosis. Conclusions We suggest a detailed picture of the changes in the kidney immune mechanisms in LN as this disease progresses.