FOLR2 and rheumatoid arthritis: Macrophages upregulate FRβ during inflammation.12 Peritoneal murine macrophages, for example, upregulate FRβ in response to challenge with thioglycollate, zymosan, or bacteria,13 and macrophages in rheumatoid arthritis and pulmonary fibrosis express functionally active FRβ that can be targeted therapeutically in an experimental setting.14–17 The idea for the study by Furusho et al was therefore simple.