Manabu Tanabe

The structure of HLA-B35 suggests that it is derived from HLA-Bw58 by two genetic mechanisms

The primary structure ofHLA-B51 andHLA-Bw52 suggested thatHLA-B51 was derived fromHLA-Bw52 by the combination of a genetic exchange withHLA-B8 and a point mutation. To investigate the evolution of theHLA-B5 cross reactive group, theHLA-B35 gene was cloned and the primary structure was determined.HLA-B35 is identical toHLA-Bw58 except in the α1 domain. The α1 domain ofHLA-B35 except Bw4/Bw6-associated amino acids is identical to that ofHLA-B51*, which was suspected to be an intermediate gene betweenHLA-B51 andHLA-Bw52. These data suggest thatHLA-B35 has evolved fromHLA-Bw58 in two steps; an in vivo replacement of the α1 domain withHLA-B51 and genetic exchange with one of theHLA-Bw6 genes. These three genes andHLA-Bw58 are postulated to share a common ancestor.

Analysis of xenoantigenicity of HLA class I molecules by a complete series of human-mouse hybrid genes

To investigate the xenoantigenicity of HLA class I antigens, a complete series of human/mouse chimeric major histocompatibility complex class I genes was constructed by using the human HLA-B7 and mouse H-2Kb genes. All of these hybrid antigens were stably expressed on L cells at high levels. Nine anti-HLA class I monoclonal antibodies, including 5 monomorphic, 3 broad polymorphic, and 2 specific polymorphic ones, were tested by binding to these cell lines. Our data suggest that the α2 domain of HLA-B7 plays an important role in the formation of the antigenic determinants recognized by all of the anti-HLA class I mAbs tested. However, the antigenic determinants of the monomorphic mAbs were complex. In some cases, all of the three extracellular domains were required for expression of the epitope. The location of xenoimmunogenic site of HLA-B7 antigen was also examined by immunizing (B6×C3H)F1 and C3H mice with the parental and hybrid antigens. Our data suggest that the a, and α2 domains of HLA-B7 must be expressed together for production of antibodies against monomorphic determinants of HLA class I antigens, while the α3 alone can induce xenoantibodies in (B6×C3H)F1 mice but not in C3H mice.

Two amino acid substitutions at residues 63 and 67 between HLA-B51 and HLA-Bw52 form multiple epitopes recognized by allogeneic T cells

HLA class I antigens are polymorphic glycoprotein expressed on the surface of human somatic cells and are coded by genes in three loci, HI_A-A, -B and -C. These molecules not only function as alloantigens but also present viral antigens to T cells. The polymorphism of these antigens relates to these functions. More than 70 serological allospecificities of HLA class I antigens are known. HLA-A2 is well studied allospecificity and 10 subtypes of this specificity are known (Ldpez de Castro, 1989). Recent studies of HLA-A2 using site-directed mutagenesis (Hogan et al. 1988, Shimojo et al. 1989) demonstrated that the residues on the c~ helical region of the 0/3/1 and o~ z domains as well as those on the/3 sheet of these domains affect the presentation of influenza virus peptides to T cells. The previous studies (Santos-Aguade et al. 1989) demonstrated that many residues on the 0/ helix and/3 sheet of the 0/1 and o~ 2 domains also affect the allorecognition of T cells. Of the HLA-B antigens, HLA-B27 was well studied and its several residues on the c~ helical region and the 13 sheet of the 0/1 and 0/2 domains were shown to affect allo-recognition of antibody and T cell (L6pez de Casto 1989). However, allodeterminants of other HLA class I antigens remain to be studied. Our previous studies of HLA-B51 and HLA-Bw52 (Hayashi et al. 1989), HLA-B35 (Ooba et ai. 1989), HLA-B SNA (Sekimata et al. 1990) and HLA-Bw53 (Hayashi et al. 1990) demonstrated that the primary structure of these molecules and HLA-Bw58 are very similar and they might have evolved from the same molecules. HLA-B51 and HLA-Bw52 differ by only two amino acids on the ~ helical region of the c~ 1 domain. HLA-B51 has Ash at residue 63 (Ash 63) and Phe at residue 67 (Phe 67), while HLA-