Primary Structure of Human Class II Histocompatibility Antigens 3rd Communication. Amino Acid Sequence Comparison between DR and DC Subclass Antigens Derived from a Lymphoblastoid B Cell Line Homozygous at the HLA Loci (HLA-A3,3; B7,7; Dw2,2; DR2,2; MT1,1; DC1,1;MB1,1)