FOLR2 and rheumatoid arthritis: For example, macrophage subpopulations were found associated with RA disease remission such as synovial tissue macrophages that are MerTK positive (MerTKpos), lymphatic vessel endothelial hyaluronan receptor 1 positive (LYVE1pos) and have a high expression of Folate Receptor (FR) beta (FRβ-high) (23).