IgA antibodies of coeliac disease patients recognise a dominant T cell epitope of A-gliadin.
BACKGROUND
In coeliac disease (CD) patients, the dominant DQ2-Alpha-I-gliadin peptide recognised by CD4 T cells is contained within peptide sequence 57-73 (p57-73) of Alpha-gliadin. This peptide sequence is also located within a 33-mer protease resistant gliadin fragment and therefore is likely to play an important role in the pathogenesis of CD.


OBJECTIVE
Our aim was to determine whether a B cell epitope was present within the immunodominant T cell epitope of Alpha-gliadin and, if so, to elucidate its sequence and determine the importance of deamidation and/or modification of the amino acid at position 65 for IgA binding.


METHODS
A cohort of CD patients, disease controls, and healthy individuals were examined. Serum IgA antibodies to the native and modified p57-73 fragment of Alpha-gliadin were analysed using enzyme linked immunosorbent assays. Peptide scanning experiments were further used to elucidate the B cell epitope.


CONCLUSIONS
IgA antibodies to p57-73 were found in 29/72 (40.2%) endomysial antibody positive patients, all of whom had CD. The peptide antibody appeared to be present when patients were on a diet containing gluten and declined on a gluten free diet. The p57-73 antibody was very specific for CD (98%) and had a sensitivity of 56%. The amino acid at position 65 was not important for IgA binding but was crucial for T cell recognition of p57-73. Pentapeptide PXPQP emerges as a potentially strong candidate for the IgA binding motif in this region of Alpha-gliadin. This study shows that a significant proportion of newly diagnosed CD patients have an antibody response to the immunodominant T cell epitope.
Department of Clinical Immunology, Churchill Hospital, Oxford Radcliffe Hospitals, Oxford OX3 7LJ, UK. BerneFerry@aol.com
E A L
EA
Bateman
B L
BL
Ferry
A
A
Hall
S A
SA
Misbah
R
R
Anderson
P
P
Kelleher
D000595:Amino Acid Sequence; D015496:CD4-Positive T-Lymphocytes / Q000276:immunology; D002446:Celiac Disease / Q000178:diet therapy / Q000276:immunology*; D004797:Enzyme-Linked Immunosorbent Assay / Q000379:methods; D018985:Epitopes, B-Lymphocyte / Q000032:analysis; D018984:Epitopes, T-Lymphocyte / Q000032:analysis* / Q000276:immunology; D005903:Gliadin / Q000235:genetics / Q000276:immunology*; D005983:Glutens / Q000008:administration & dosage; D006801:Humans; D007070:Immunoglobulin A / Q000276:immunology*; D008969:Molecular Sequence Data; D010446:Peptide Fragments / Q000235:genetics / Q000276:immunology
D018985:Epitopes, B-Lymphocyte; D018984:Epitopes, T-Lymphocyte; D007070:Immunoglobulin A; D010446:Peptide Fragments; D005983:Glutens; D005903:Gliadin