MHC class II receptor activity MHC class II protein complex obsolete MHC class II receptor activity true MHC class II receptor activity This term was made obsolete because it was defined ambiguously, and has therefore been used incorrectly in annotations. To update annotations of gene products that act as receptors for MHC class II protein complexes, use the molecular function term 'MHC class II receptor activity ; GO:0032395'; to update annotations of gene products which are components of MHC class II protein complexes, use the cellular component term 'MHC class II protein complex ; GO:0042613'. OBSOLETE. A major histocompatibility complex class II receptor. These display processed antigens from virally-infected or transformed cells. Class-II-positive cells ('antigen-presenting cells') can take up antigens from outside by endocytosis, degrade them into small peptides, and re-export the peptides (now bound to MHC class II protein) to the cell surface. These peptide-MHC class II complexes can then be recognized by specific CD4+ lymphocytes. class II major histocompatibility complex antigen molecular_function major histocompatibility complex class II receptor GO:0045012