HLA is present on-

Reference :Robbins basic pathology 9th edition pg no 102 :loci named HLA A,HLA B and HLA C.Each of these molecules it&;s a hetero dimer consisting of polymorphic 44kDa alpha chain noncovalently associated with an invariant 12 kDa beta2 microglobulin polypeptide (encoded by a separate gene on chromosome 15)