In the paper below, we provide the first evidence that FR-β-positive macrophages are abundant in virtually all autoimmune diseases, including rheumatoid arthritis, Crohn’s disease, ulcerative colitis, idiopathic pulmonary fibrosis, nonspecific interstitial pneumonia, chronic obstructive pulmonary disease, systemic lupus erythematosus, psoriasis, and scleroderma. Here, FOLR2 is linked to systemic lupus erythematosus.