B2M and neoplasm: β2M also complexes with many non-classical MHC-I like molecules (MHC-Ib) such as CD1, MR1 (33), HLA-E, -F, -G (34, 35), neonatal Fc receptor (FcRn) (36–38), and HFE/HLA-H that are involved in mucosal immunity, tumor surveillance, maternofetal immune tolerance, immunoglobulin and albumin homeostasis as well as iron metabolism.