HLA-DR binding analysis of peptides from islet antigens in IDDM.
HLA molecules are essential for thymic education and HLA restriction of T-cell responses. We therefore analyzed the HLA-DR binding affinities of synthetic peptides covering the entire sequences of GAD65, islet cell antigen 69 (ICA69), and (pro)insulin, which are candidate antigens in the autoimmune process of T-cell-mediated destruction of the pancreatic beta-cells. Subsequently, peptide HLA-DR binding was correlated to peptide antigenicity by comparing known T-cell epitopes with their HLA-binding affinities defined in this study. The results demonstrate the following. 1) (Pro)insulin peptides display a strong binding affinity for HLA-DR2, which is associated with negative genetic predisposition to IDDM, whereas poor binding was observed for HLA-DR molecules neutrally or positively associated with IDDM. This suggests that the absence of insulin-reactive T-cells in DR2+ individuals may be explained by negative selection on high-affinity DR2 binding insulin peptides. 2) Most autoantigenic peptides display promiscuous HLA-DR binding patterns. This promiscuity in itself is not sufficient to explain the genetic association of HLA-DR with development of IDDM. 3) HLA-DR3 binding of autoantigenic GAD65 peptides is relatively weak compared with that of other known T-cell epitopes. 4) All peptide epitopes recognized by HLA-DR-restricted T-cells from either IDDM patients or GAD65-immunized HLA-DR transgenic mice bind with high affinity to their HLA-DR restriction molecule (P < 0.0006). In contrast, T-cell epitopes recognized by nondiabetic controls bind DR molecules with weak or undetectable affinity. These results thus indicate a strong correlation between antigenicity and HLA-DR binding affinity of GAD65 peptides in IDDM. Furthermore, negative thymic selection of insulin peptides in low-risk (HLA-DR2 expressing) subjects may explain the lack of autoreactivity to insulin in such individuals.
Geluk
A
A
Department of Immunohematology and Blood Bank, Leiden University Medical Center, The Netherlands. geluk@rullf2.medfac.leidenuniv.nl
van Meijgaarden
K E
KE
Schloot
N C
NC
Drijfhout
J W
JW
Ottenhoff
T H
TH
Roep
B O
BO
D000595:Amino Acid Sequence; D000818:Animals; D001324:Autoantigens / Q000737:chemistry / Q000378:metabolism*; D003922:Diabetes Mellitus, Type 1 / Q000276:immunology*; D005968:Glutamate Decarboxylase / Q000737:chemistry / Q000276:immunology; D006684:HLA-DR Antigens / Q000378:metabolism*; D015798:HLA-DR1 Antigen / Q000378:metabolism; D015802:HLA-DR2 Antigen / Q000378:metabolism; D015803:HLA-DR3 Antigen / Q000378:metabolism; D015804:HLA-DR4 Antigen / Q000378:metabolism; D006801:Humans; D007328:Insulin / Q000737:chemistry / Q000276:immunology; D007515:Islets of Langerhans / Q000276:immunology; D051379:Mice; D008822:Mice, Transgenic; D008969:Molecular Sequence Data; D010446:Peptide Fragments / Q000737:chemistry / Q000276:immunology* / Q000378:metabolism; D011384:Proinsulin / Q000737:chemistry / Q000276:immunology; D011485:Protein Binding; D013601:T-Lymphocytes / Q000276:immunology
D001324:Autoantigens; D006684:HLA-DR Antigens; D015798:HLA-DR1 Antigen; D015802:HLA-DR2 Antigen; D015803:HLA-DR3 Antigen; D015804:HLA-DR4 Antigen; D007328:Insulin; D010446:Peptide Fragments; D011384:Proinsulin; D005968:Glutamate Decarboxylase