V-set and immunoglobulin domain-containing 4 (VSIG4) is a complement receptor of the immunoglobulin superfamily (CRIg) that is specifically expressed in resting tissue-resident macrophages . Notably, CRIg is expressed in monocyte-derived macrophages but not in human and mouse monocytes. VSIG4 can suppress T cell proliferation and promote Foxp3+ regulatory T cell (Tregs) differentiation by binding an unidentified receptor on T cells . VSIG4 has been implicated in a variety of diseases, particularly those involving immune dysregulation and inflammation, such as non-alcoholic steatohepatitis, rheumatoid arthritis, and obesity-related metabolic disorders . Recently, VSIG4+ tumor-associated macrophages (TAMs) have been identified as a specific subset that infiltrates aggressive cancers, including anaplastic thyroid cancer (ATC). (PMID: 37153746,PMID: 39920772)