Some recent studies add complexity to this issue by reporting that M-CSF-polarized FRβ-expressing M2 macrophages demonstrated a high pro-inflammatory response to TLR ligands and complex IgG and/or autoantibodies to citrullinated protein immune complexes (ACPA-IC) as commonly present in RA [25, 26]. Here, PRTN3 is linked to rheumatoid arthritis.