Major Histocompatibility Antigens Are

Major histocompatibility antigens are

A) antigens that provoke allergic reactions.
B) antigens that must be processed by cells called histiocytes in order to be recognized by the immune system.
C) antigens attached to foreign invaders.
D) glycoproteins found in the cytoplasmic membranes of most vertebrate animal cells.
E) not really antigens, but rather antibodies produced to mask foreign antigens.