Major Differences in Antigen-Processing Correlate with a Single Arg71↔Lys Substitution in HLA-DR Molecules Predisposing to Rheumatoid Arthritis and with Their Selective Interactions with 70-kDa Heat Shock Protein Chaperones

Abstract

Several HLA-DR alleles are genetically associated with rheumatoid arthritis. DRB1*0401 predominates in Northern Europe and has a characteristic 70QKRAA motif. This sequence contacts bound peptides and the TCR. Further interactions have been suggested with additional proteins during Ag loading. We explored the much stronger processing/presentation of full-length recombinant human acetylcholine receptor α subunit to a specific T cell clone by APC from DRB1*0401+ than *0408+ donors. Using DR*04 transfectants, we show that this difference results largely from the single Lys71↔Arg interchange (0401↔0408), which scarcely affects epitope binding, rather than from any other associated polymorphism. Furthermore, we proved our recombinant polypeptides to contain the Escherichia coli 70-kDa heat shock protein molecule DnaK and its requirement for efficient processing and presentation of the epitope by DRB1*0401+ cells. According to a recent report, 70-kDa heat shock protein chaperones preferentially bind to the QKRAA, rather than the QRRAA, motif. Variations between the shared epitope motifs QKRAA and QRRAA are emphasized by underlining. We propose that such interactions enhance the intracellular epitope loading of *0401 molecules. They may thus broaden immune responses to pathogens and at least partially explain the distinct contributions of DRB1*0401 and other alleles to disease predisposition.

A heat shock protein gene (Hsp70.1) is critically involved in the generation of the immune response to myelin antigen

“…It has been shown for both MHC class I-and II-dependent systems that hsp70 complexes with proteins are more immunogenic than proteins alone [20][21][22][23][24][25][26][27][28][29]. This has been related to enhancement of antigen presentation by hsp.…”

“…While most data on the contribution of hsp-peptide interactions have addressed immune responses involving MHC class Idependent pathways [21][22][23][24], more recent results from this [25], and other [26][27][28][29] laboratories indicate that hsp are also capable of participating in antigen presentation in MHC class II-dependent pathways. In this respect, hsp70 is a major hsp implicated in the formation of immunogenic complexes and the facilitation of MHC presentation.…”

The heat shock protein Hsp70 enhances antigen-specific proliferation of human CD4+ memory T cells

“…It was shown that overexpression of the constitutively expressed Hsc73 in a macrophage cell line led to an increased presentation of exogenous antigen via MHC class II [13]. Moreover, E. coli HSP70 DnaK was found to enhance the processing and presentation of exogenous antigen to a human CD4 + T cell clone, whereas the effect was dependent on the allelic variants of HLA-DR [14]. A direct interaction between HLA-DR-derived peptide fragments and HSP70 molecules was demonstrated by our group, showing that only peptide fragments derived from HLA-DR molecules associated with protection from rheumatoid arthritis (RA) did not bind to HSP70 [15].…”

Immungenetik—

“…Dieselbe T-Zelle kann ein "high responder" oder ein "low responder" sein! Wir konnten mit Transfektanten zeigen, dass der Unterschied nur vom Austausch Lys 71 ↔ Arg 71 (*0401 ↔ *0408) herrührt, der die Bindung des Epitops nicht beeinträchtigt, und dass die rekombinante a-Untereinheit des AChR das E. coli DnaK enthielt [20]. Dieses ist für effizientes Prozessieren des Antigens und Präsentieren des Epitops durch *0401 + APZ absolut notwendig [20].…”

“…Wir konnten mit Transfektanten zeigen, dass der Unterschied nur vom Austausch Lys 71 ↔ Arg 71 (*0401 ↔ *0408) herrührt, der die Bindung des Epitops nicht beeinträchtigt, und dass die rekombinante a-Untereinheit des AChR das E. coli DnaK enthielt [20]. Dieses ist für effizientes Prozessieren des Antigens und Präsentieren des Epitops durch *0401 + APZ absolut notwendig [20]. Wir nehmen daher an, dass sich das Antigen in einem Komplex mit DnaK befand, aus dem heraus es in die Tasche des *0401-Moleküls geladen werden konnte, nicht aber in die des *0408-Moleküls (Abb.…”