Blackwell Publishing Journal Backfiles 1879-2005
The T cell antigen receptor (TCR) is a multimeric complex composed of an antigen-binding clonotypic heterodimer and a signal transducing complex consisting of the CD3 dimers (CD3γε and CD3δε) and a TCR-ζ homodimer. In all jawed vertebrates there are two T cell lineages, αβ and γδ, distinguished by the clonotypic subunits contained within their TCRs (TCR-α and -β or TCR-γ and -δ, respectively). A third receptor complex, the preTCR, is only expressed on immature T cells. The preTCR, which contains the invariant pre-Tα (pTα) chain in lieu of TCR-α, plays a critical role in the early development of αβ lineage cells. The subunit composition of the signal transducing complexes of the pre-, αβ- and γδTCRs was previously thought to be identical. However, recent data demonstrate that there are significant differences in the signal transducing complexes of these three TCRs. For example, αβTCRs contain both CD3γε and CD3δε dimers, whereas γδTCRs contain only CD3γε dimers. Moreover, preTCR function appears to be unaffected in the absence of CD3δ, suggesting that CD3δε dimers are dispensable for pre-TCR assembly. In this review, we summarize current data relating to the subunit composition of the pre-, αβ- and γδTCRs and discuss how these structural differences may impact receptor signaling and αβ/γδ lineage determination.
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