Distinctive features of the alpha 1-domain alpha helix of HLA-C heavy chains free of beta 2-microglobulin

Hum Immunol. 1996 Apr;46(2):69-81. doi: 10.1016/0198-8859(96)00011-0.


Only a few monoclonal antibodies are available with a restricted specificity to HLA-C products. In the present report, we demonstrate that antibody L31, previously shown to react with beta 2m-less (free) class I MHC heavy chains, binds to an epitope (residues 66-68 of the alpha 1 domain alpha helix) present on all the HLA-C alleles corresponding to the accepted (CW1 through CW8) serologic specificities, and on a few HLA-B heavy chains sharing with HLA-C an aromatic residue at position 67. Extensive IEF blot testing of HLA homozygous, EBV-transformed B-lymphoid cells indicates that HLA-C molecules are present at significantly lower levels than HLA-B polypeptides not only at cell surface, as previously demonstrated, but also in total cellular extracts. Testing of metabolically labeled HLA-CW1, -CW5, and -CW6 transfectants and HLA homozygous lymphoid cells, particularly HLA-CW1-expressing cells, demonstrates that the L31 epitope is present on a subpopulation of naturally occurring HLA-C molecules distinct from that identified by antibody W6/32 to beta 2m-associated heavy chains. Pulse-chase experiments demonstrate that this epitope is transiently made available to antibody binding at early biosynthetic stages, but becomes hidden upon assembly with beta 2m. Thus, free HLA-C and other Y/F67+ heavy chains are characterized by distinctive antibody binding features in a region (residues 66-68) included in a previously identified HLA-C restricted motif, which has been suggested to be the primary cause of distinctive features of the antigen-binding groove, low affinity for endogenous peptide antigens and beta 2m, and preferential uptake of exogenous peptides, possibly of viral origin. We also show that HLA-CW1 heavy chains, both free and beta 2m associated, acquire sialilation. Free HLA-CW1 heavy chains are expressed at the cell surface even when unsialilated, albeit at low levels.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Antibodies, Monoclonal / immunology
  • B-Lymphocytes / immunology
  • Cell Line, Transformed
  • Epitope Mapping / methods
  • Epitopes / immunology*
  • HLA-C Antigens / biosynthesis
  • HLA-C Antigens / immunology*
  • Humans
  • Isoelectric Focusing / methods
  • Protein Structure, Secondary*
  • beta 2-Microglobulin / deficiency*
  • beta 2-Microglobulin / immunology


  • Antibodies, Monoclonal
  • Epitopes
  • HLA-C Antigens
  • beta 2-Microglobulin