Single-cell RNA sequencing (scRNA-seq) of PBMCs from RA patients has identified 18 immune cell subsets, revealing disease-associated signatures such as IFN-induced transmembrane 3 (IFITM3)-expressing monocytes, increased CD4+ effector memory T cells in active disease, and reduced nonclassical monocytes during remission [126]. Here, CD4 is linked to rheumatoid arthritis.