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14
T CELL RESPONSES TO GLUTEN PEPTIDES
non-deamidated gluten were also observed. These results indicate that a large
proportion of the gluten specific responses are directed to deamidated gluten but that
responses to non-deamidated gluten are also common.
Extensive testing of the T cell clones against the 3 known HLA-DQ2 restricted T
cell stimulatory gliadin derived peptides indicated that the large majority of the T cell
clones did not respond to these peptides, and were thus likely reactive towards yet
unidentified gluten peptides. To characterize these novel peptides we have used two
different methods. First, we purified and characterized T cell stimulatory gluten
epitopes from pepsin/trypsin digests of (tTG-) gluten by rpHPLC and mass
1-2
spectrometry as described . This method led to the characterization of 3 novel T cell
stimulatory peptides. Second, we tested the T cell clones against a set of 250 synthetic
gluten peptides, representing gliadin and glutenin sequences. This method led to the
identification of 3 additional novel T cell stimulatory peptides.
Subsequently we tested the response of the T cell clones to the identified peptides in
deamidated and non-deamidated form. The T cell response towards 3 peptides required
prior deamidation. In contrast, the response to 2 peptides was found to be largely
indifferent to deamidation. Finally, deamidation abolished the response to the sixth
peptide. Thus, the effect of deamidation by tTG on gluten specific T cell stimulation is
heterogeneous and can be positive, neutral and negative.
Subsequently the gluten specific T cell clones of all patients were tested against the
3-5
previously characterized HLA-DQ2 restricted gluten peptides as well as against the
peptides reported in the present study. While responses to some peptides were found in
one patient only, responses to other peptides were found in various patients and these
may thus represent more immunodominant peptides. T cell responses towards the a-
gliadin peptides which have been reported to be immunodominant in adult patients
were found in three paediatric patients, among whom the identical twins. In these 9
patients we observed 8 distinct reactivity patterns towards the gluten peptides (Table).
Altogether, these results indicate a highly diverse response against the gluten peptides.
These results indicate a discrepancy between the specificity of adult and paediatric
gluten specific T cell responses. While immunodominant responses to a particular a-
gliadin peptide are found in adult patients, the response in paediatric patients appears
more diverse. Our results also indicate that T cell responses to peptides other than the
immunodominant a-gliadin peptide can lead to disease. Moreover, our results
demonstrate that responses to non-deamidated peptides are frequently found,
suggesting that native gluten peptides are immunogenic in celiac disease patients.
The discrepancy between the specificity of the adult and paediatric gluten specific T
cell response could be explained by a deamidation driven narrowing of the gluten
response towards immunodominant T cell stimulatory peptides after initiation of
disease by responses towards a diverse repertoire of gluten peptides.
Acknowledgements
This study was financially supported by the European Community project no. BMH
CT-98, a grant from the Dutch Digestive Disease Foundation and the University of
Leiden.