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Chain
Signaling Motifs in Selection of the T Cell Repertoire
By




From the * Division of Hematologic Products, Center for Biologics Evaluation and Research, Food and
Drug Administration, Bethesda, Maryland 20892; and the Immature thymocytes undergo a selection process within the thymus based on their T cell antigen receptor (TCR) specificity that results either in their maturation into functionally competent, self-MHC-restricted T cells (positive selection) or their deletion (negative selection). The
outcome of thymocyte selection is thought to be controlled by signals transduced by the TCR that
vary in relation to the avidity of the TCR-ligand interaction. The TCR is composed of four
distinct signal transducing subunits (CD3-
Laboratory of Mammalian Genes and
Development, National Institute of Child Health and Human Development, National Institutes of
Health, Bethesda, Maryland 20892
, -
, -
, and
) that contain either one (CD3-
, -
,
-
) or three (-
) signaling motifs (ITAMs) within their intracytoplasmic domains. A possible
function for multiple TCR ITAMs could be to amplify signals generated by the TCR during selection. To determine the importance of the multiple TCR-
chain ITAMs in thymocyte selection, transgenes encoding
/
TCRs with known specificity were bred into mice in which
chains lacking one or more ITAMs had been genetically substituted for endogenous
. A direct
relationship was observed between the number of
chain ITAMs within the TCR complex and the efficiency of both positive and negative selection. These results reveal a role for multiple
TCR ITAMs in thymocyte selection and identify a function for TCR signal amplification in
formation of the T cell repertoire.
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