A previous study identified four transcriptionally distinct monocyte subsets in the scRNA-seq data: IL1B+ monocytes, NURP1+ monocytes, C1QA+ monocytes, and IFN-act SPP1+ monocytes, and leukocyte-rich RA have a greater abundance of IL1B+ monocytes and IFN-act SPP1+ monocytes12. Here, SPP1 is linked to rheumatoid arthritis.