Distinctive Features of the α1-Domain a Helix of HLA-C Heavy Chains Free of β2-Microglobulin
1996; Elsevier BV; Volume: 46; Issue: 2 Linguagem: Inglês
10.1016/0198-8859(96)00011-0
ISSN1879-1166
AutoresAndrea Setini, Alberto Beretta, C. De Santis, Raffaella Meneveri, Aline Martayan, Maria Cristina Mazzilli, Ettore Appella, Antonio G. Siccardi, Pier Giorgio Natali, Patrizio Giacomini,
Tópico(s)Immunotherapy and Immune Responses
ResumoOnly 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 β2m-less (free) class I MHC heavy chains [23], binds to an epitope (residues 66–68 of the α1 domain α 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 HLACW1, -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 β2m-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 β2m. 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 [17], which has been suggested to be the primary cause of distinctive features of the antigenbinding groove, low affinity for endogenous peptide antigens and β2m, and preferential uptake of exogenous peptides, possibly of viral origin. We also show that HLACW1 heavy chains, both free and β2m associated, acquire sialilation. Free HLA-CW1 heavy chains are expressed at the cell surface even when unsialilated, albeit at low levels.
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