Differential antibody binding to the surface alphabetaTCR.CD3 complex of CD4+ and CD8+ T lymphocytes is conserved in mammals and associated with differential glycosylation.

We have previously shown that the surface alphabeta T cell antigen receptor (TCR).CD3 complex borne by human CD4(+) and CD8(+) T lymphocytes can be distinguished using mAbs. Using two unrelated sets of antibodies, we have now extended this finding to the surface alphabetaTCR.CD3 of seven additional mammalian species (six non-human primates and the mouse). We have also produced data supporting that differential glycosylation of the two main T cell subsets is involved in the observed TCR.CD3 antibody-binding differences in humans. First, we show differential lectin binding to human CD4(+) versus CD8(+) T lymphocytes, particularly with galectin 7. Second, we show that certain lectins can compete differentially with CD3 mAb binding to human primary CD4(+) and CD8(+) T lymphocytes. Third, N-glycan disruption using swainsonine was shown to increase mAb binding to the alphabetaTCR.CD3. We conclude that the differential antibody binding to the surface alphabetaTCR.CD3 complex of primary CD4(+) and CD8(+) T lymphocytes is phylogenetically conserved and associated with differential glycosylation. The differences may be exploited for therapeutic purposes, such as T cell lineage-specific immunosuppression of graft rejection. Also, the impact of glycosylation on CD3 antibody binding requires a cautious interpretation of CD3 expression levels and T cell numbers in clinical diagnosis.

Overlapping functions of human CD3delta and mouse CD3gamma in alphabeta T-cell development revealed in a humanized CD3gamma-mouse.

Humans lacking the CD3gamma subunit of the pre-TCR and TCR complexes exhibit a mild alphabeta T lymphopenia, but have normal T cells. By contrast, CD3gamma-deficient mice are almost devoid of mature alphabeta 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 CD3delta chain replaces CD3gamma during alphabeta T-cell development. To determine whether human CD3delta (hCD3delta) functions in a similar manner in the mouse in the absence of CD3gamma, we introduced an hCD3delta transgene in mice that were deficient for both CD3delta and CD3gamma, in which thymocyte development is completely arrested at the DN stage. Expression of hCD3delta efficiently supported pre-TCR-mediated progression from the DN to the CD4(+)CD8(+) double-positive (DP) stage. However, alphabetaTCR-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 CD3gamma-deficient TCR complexes that had incorporated hCD3delta displayed abnormalities in structural stability resembling those of T cells from CD3gamma-deficient humans. Taken together, these data demonstrate that CD3delta and CD3gamma play a different role in humans and mice in pre-TCR and TCR function during alphabeta T-cell development.