Subunit Composition of Pre–T Cell Receptor Complexes Expressed by Primary Thymocytes: CD3δ Is Physically Associated but Not Functionally Required

Abstract

Maturation of immature CD4−CD8− (DN) thymocytes to the CD4+CD8+ (DP) stage of development is driven by signals transduced through a pre–T cell receptor (TCR) complex, whose hallmark is a novel subunit termed pre-Tα (pTα). However, the precise role of pre-TCRs in mediating the DN to DP transition remains unclear. Moreover, progress in understanding pre-TCR function has been hampered thus far because previous attempts to demonstrate expression of pTα-containing pre-TCRs on the surface of normal thymocytes have been unsuccessful. In this report, we demonstrate for the first time that pTα-containing pre-TCR complexes are expressed at low levels on the surface of primary thymocytes and that these pre-TCR complexes comprise a disulfide-linked pTα–TCR-β heterodimer associated not only with CD3-γ and -ε, as previously reported, but also with ζ and δ. Interestingly, while CD3-δ is associated with the pre-TCR complex, it is not required for pre-TCR function, as evidenced by the generation of normal numbers of DP thymocytes in CD3-δ–deficient mice. The fact that any of the signaling components of the pre-TCR are dispensable for pre-TCR function is indeed surprising, given that few pre-TCR complexes are actually expressed on the surface of primary thymocytes in vivo. Thus, pre-TCRs do not require the full array of TCR-associated signaling subunits (γ, δ, ε, and ζ), possibly because pTα itself possesses signaling capabilities.

Impact of early expression of TCR α chain on thymocyte development

“…These results are therefore consistent with the notion that the § g TCR and pre-TCR elicit different signals for thymocyte development [12] despite the sharing of several signaling components [33]. However, it remains to be determined whether the difference between the § g TCR and pre-TCR results from the direct recruitment of distinct signaling molecules [34][35][36][37][38], or the differential abilities of pT § and TCR § chain to target the receptor complex to distinct cellular locations [9,11,39], or both.…”

Opposite Ability of Pre-TCR and αβTCR to Induce Apoptosis

“…The SL12 cell line was derived from a SCID mouse spontaneous thymoma, and its phenotype corresponds to the CD25 ϩ CD44 stage of T cell development (pT␣ expression, CD4 (17,18). SL12 cells were stably transfected either with the pXS expression vector alone (SL12 Neo), or with the same vector encoding the ␤-chain of the 2B4 TCR (19), allowing pre-TCR surface expression (SL12␤.12) (17).…”

Synergistic Effects of Interleukin-7 and Pre-T Cell Receptor Signaling in Human T Cell Development

“…Many studies use antibody clones specifically recognizing CD3⑀ paired with CD3␦ or CD3␥; the anti-CD3 antibody clone used in our study does not require such pairing. Moreover, pre-TCR does not require CD3␦ for its function (64). Unlike murine pre-T␣, human pre-T␣ has an endoplasmic reticulum retention signal in its cytoplasmic domain and is strongly associated with the CD3 chain (54,55).…”