Hypothesis: TCR signal transduction--A novel tri-modular signaling system

The expression pattern of CD3 chain genes in fetal/maternal interface

In order to investigate the features of T-cell immune status in human placenta, the expression levels of CD3-gamma, -delta, -epsilon and -zeta chain genes in placenta were analyzed by real-time PCR. Umbilical cord blood obtained at delivery from the full-term healthy babies was used as a control. The beta2-microglobulin gene was employed as an endogenous reference, and the evaluations of mRNA expression level of each CD3 gene were used by the 2(-ΔC(t))×100% method. The expression level of CD3-gamma, -epsilon and -zeta genes (mean rank is 0.13, 0.34, and 0.49 respectively) from placenta were significantly lower than those from CB (P<0.0001). CD3-delta genes (mean rank is 5.71) expressed stronger from placenta than from CB (P = 0.0.895). Thus, the expression pattern of the four CD3 genes was presented as delta>zeta>epsilon> gamma from placenta and epsilon>gamma>zeta>delta from CB on the contrary. In conclusion, the present study characterized the expression pattern of CD3-gamma, -delta, -epsilon and -zeta chain genes from placenta, which contributes to further understanding of the features of T-cell immune status in placenta.

CD3γ-independent pathways in TCR-mediated signaling in mature T and iNKT lymphocytes

Antigen recognition by T-lymphocytes through the T-cell antigen receptor, TCR-CD3, is a central event in the initiation of an immune response. CD3 proteins may have redundant as well as specific contributions to the intracellular propagation of TCR-mediated signals. However, to date, the relative role that each CD3 chain plays in signaling is controversial. In order to examine the roles of CD3γ chain in TCR signaling, we analyzed proximal and distal signaling events in human CD3γ(-/-) primary and Herpesvirus saimiri (HVS)-transformed T cells. Following TCR-CD3 engagement, certain early TCR signaling pathways (ZAP-70, ERK, p38 and mTORC2 phosphorylation, and actin polymerization) were comparable with control HVS-transformed T cells. However, other signaling pathways were affected, such TCRζ phosphorylation, indicating that the CD3γ chain contributes to improve TCR signaling efficiency and survival. On the other hand, CD3γ(-/-) primary invariant NKT cells (iNKT cells) showed a normal expansion in response to alpha-galactosylceramide (α-GalCer) and TCRVβ11(bright) iNKT cells were preferentially selected in this in vitro culture system, perhaps as a consequence of selective events in the thymus. Our results collectively indicate that a TCR lacking CD3γ can propagate a number of signals through the remaining invariant chains, likely the homologous CD3δ chain, which replaces it at the mutant TCR.