Signaling Through a CD3γ-Deficient TCR/CD3 Complex in Immortalized Mature CD4+ and CD8+ T Lymphocytes

Abstract

The biologic role of each CD3 chain and their relative contribution to the signals transduced through the TCR/CD3 complex and to downstream activation events are still controversial: they may be specialized or redundant. We have immortalized peripheral blood CD4+ and CD8+ T lymphocytes from a human selective CD3γ deficiency using Herpesvirus saimiri. The accessibility of the mutant TCR/CD3 complex to different Abs was consistently lower in immortalized CD8+ cells when compared with CD4+ cells, relative to their corresponding CD3γ-sufficient controls. Several TCR/CD3-induced downstream activation events, immediate (calcium flux), early (cytotoxicity and induction of surface CD69 or CD40L activation markers or intracellular TNF-α) and late (proliferation and secretion of TNF-α), were normal in γ-deficient cells, despite the fact that their TCR/CD3 complexes were significantly less accessible than those of controls. In contrast, the accumulation of intracellular IL-2 or its secretion after CD3 triggering was severely impaired in γ-deficient cells. The defect was upstream of protein kinase C activation because addition of transmembrane stimuli (PMA plus calcium ionophore) completely restored IL-2 secretion in γ-deficient cells. These results suggest that the propagation of signals initiated at the TCR itself can result in a modified downstream signaling cascade with distinct functional consequences when γ is absent. They also provide evidence for the specific participation of the CD3γ chain in the induction of certain cytokine genes in both CD4+ and CD8+ human mature T cells. These immortalized mutant cells may prove to be useful in isolating cytosolic signaling pathways emanating from the TCR/CD3 complex.