Abstract
Humans lacking the CD3γ subunit of the pre-TCR and TCR complexes exhibit a mild αβ T lymphopenia, but have normal T cells. By contrast, CD3γ-deficient mice are almost devoid of mature αβ T cells due to an early block of intrathymic development at the CD4–CD8– double-negative (DN) stage. This suggests that in humans but not in mice, the highly related CD3δ chain replaces CD3γ during αβ T-cell development. To determine whether human CD3δ (hCD3δ) functions in a similar manner in the mouse in the absence of CD3γ, we introduced an hCD3δ transgene in mice that were deficient for both CD3δ and CD3γ, in which thymocyte development is completely arrested at the DN stage. Expression of hCD3δ efficiently supported pre-TCR–mediated progression from the DN to the CD4+CD8+ double-positive (DP) stage. However, αβTCR-mediated positive and negative thymocyte selection was less efficient than in wild-type mice, which correlated with a marked attenuation of TCR-mediated signaling. Of note, murine CD3γ-deficient TCR complexes that had incorporated hCD3δ displayed abnormalities in structural stability resembling those of T cells from CD3γ-deficient humans. Taken together, these data demonstrate that CD3δ and CD3γ play a different role in humans and mice in pre-TCR and TCR function during αβ T-cell development.
Double Negative (DN) αβ T Cells: misperception and overdue recognition