download report - Istituto Pasteur

P a r t i c i p a n t s :
Maria Teresa Fiorillo, researcher; Fabiana Paladini, post-doc
fellow; Francesca Belfiore, Elisa Cocco, Adriana
Magnacca, Elisa Nurzia, PhD students.
C o l l a b o r a t i o n s :
Istituto di Biologia Cellulare, CNR, Roma (Dr. Isabella Cascino);
Department for Crystallography, FU Berlin, Germany (Prof.
Wolfang Saenger); Institut für Immungenetik,
Universitätsklinikum Charité Humboldt-Universität zu Berlin,
Berlin, Germany (Prof. Andreas Ziegler, Dr Barbara
Uchanska-Ziegler); Dipartimento di Scienze Mediche, Università
di Cagliari (Prof. Alessandro Mathieu).
Report of activity
The project plan was subdivided in three different
parts:
Analysis of T cell responses specific for
peptides sharing homology with the viral
peptide pLMP2 in patients with AS versus
healthy controls
The viral pLMP2 (RRRWRRLTV) and the self
pVIPR (RRKWRRWHL) peptides are unusually
rich in arginines. This amino acid can undergo
post-translational modifications consisting in citrullination.
These modifications could confer some
new antigenic properties to these peptides making
the immune system able to recognize them as
novel antigens and mount a cytotoxic T cell
response (Beltrami et al., J Biol Chem. 2008,
283:27189-99).
We therefore have synthesized new peptides possessing
citrulline instead of arginine, either in single
(p1; p5 and p6) or in multiple positions (p1 and
p5; p1 and p6; p5 and p6). One of these peptides,
pVIPR-U5 (RRKWURWHL; U = citrulline), has
already been analysed both at functional and crystallographic
levels to verify whether the exchange of
Principal investigator: Rosa Sorrentino
Professor of Pathology
Dipartimento di Biologia Cellulare e dello Sviluppo
Tel: (+39) 06 49917706; Fax: (+39) 06 49917594
rosa.sorrentino@uniroma1.it
105
Cellular and molecular immunology - AREA 5
The role of HLA-B27 in autoimmunity: from the genetics to the
function
arginine to citrulline affects the display of this peptide
by two human major histocompatibility antigen
class I subtypes, HLA-B*2705 and HLA-B*2709.
The crystal structures show that a modified selfpeptide,
pVIPR-U5 (RRKWURWHL; U = citrulline)
is presented by the two HLA-B27 molecules
in distinct conformations. These binding modes differ
not only drastically from each other but also
from the conformations exhibited by the non-citrullinated
peptide in a given subtype. The differential
reactivity of HLA-B27-restricted cytotoxic T cells
with modified or unmodified pVIPR supports the
structural findings and shows that the presentation
of citrullinated peptides has the potential to influence
immune responses. Furthermore, citrullinated
peptides such as pVIPR-U5 and pVIPR-U5+U6
have been tested for their ability to induce self-reactivity
in B*2705 patients with AS. So far, we have
observed CD8+ T cell responses in 2 out of 5
patients and the responsive CTL lines have shown
either specificity for the citrullinated forms of
pVIPR or cross-reactivity with the native peptide.
This result supports the possibility that some circustances
such as chronic inflammatory conditions
that occur in AS could favor the activity of PAD
(peptidylarginine deiminases), the enzyme involved
in the arginine to citrulline conversion. T cells from
B*2709 positive individuals have also been stimulated
with citrullinated forms of pVIPR and so far no
reactivity has been detected. In progress is a large
screening in which CTL lines primarily driven by
pLMP2, pVIPR and pVIPR-U5 or pVIPR-U5+U6
are assayed against the complete panel of citrullinated
pVIPR and pLMP2 analogs (the arginine at
each position substituted by citrullines). These
immunological results will be combined with structural
data assessing the ability of the citrullinated
peptides to form a stable complex with either
B*2705 and B*2709 molecules and with spettroscopic
measurements,i.e. circular dichroism (CD)
and differential scanning calorimetric (DSC).