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7
Analysis of the a=b T-Cell Receptor
Repertoire in HIV Infection
Hugo Soudeyns
Unit d'immunopathologie virale, Centre de recherche de l'Hà pital Sainte-
Justine; Departments de microbiologie & immunologie et de pÂdiatrie, FacultÂ
de mÂdicine, Universit de MontrÂal, MontrÂal, Quebec, Canada
INTRODUCTION
Antigens are presented to the immune system in the form of short peptides
associated with class I or class II major histocompatibility complex (MHC)
components. Recognition of MHC-peptide complexes is mediated by the T-cell
receptor ( TCR), a disul®de-linked heterodimer expressed at the surface of most
thymocytes and peripheral T cells. TCRs composed of g and d chains (``g=d
TCRs'') are expressed by small subsets of peripheral and tissue-resident lym-
phocytes, and recognize soluble or tissue-associated antigens, including non-
peptidic components of bacterial cell walls (Kaufmann, 1996; Tanaka et al.,
1995). a=b TCRs recognize class I and class II peptides-MHC complexes ( Davis
and Bjorkman, 1988; Yague et al., 1985). The TCR is expressed at the cell
surface in association with a set of invariant molecules collectively referred to
as CD3 (Cosson et al., 1991). Upon cognate interaction between the TCR and
peptide-MHC, complex supramolecular clustering is followed by conforma-
tional changes in the TCR and CD3 complex, resulting in the transduction of
transmembrane activation signals to the T cell (Grakoui et al., 1999; Weiss and
Littman, 1994). T-cell activation leads to increase in cell size and metabolism,
enhancement of cell-surface expression of TCR and coreceptors, and expression
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