Isopentenyl Pyrophosphate, a Mycobacterial Non-peptidic Antigen, Triggers Delayed and Highly Sustained Signaling in Human γδ T Lymphocytes without Inducing Down-modulation of T Cell Antigen Receptor

Abstract

The Vγ9Vδ2 T cell subset, which represents up to 90% of the circulating γδ T cells in humans, was shown to be activated, via the T cell receptor (TcR), by non-peptidic phosphorylated small organic molecules. These phosphoantigens, which are not presented by professional antigen-presenting cells, induce production of high amounts of interferon-γ and tumor necrosis factor (TNF-α). To date, the specific signals triggered by these antigens have not been characterized. Here we analyze proximal and later intracellular signals triggered by isopentenyl pyrophosphate (IPP), a mycobacterial antigen that specifically stimulates Vγ9Vδ2 T cells, and compare these to signals induced by the non-physiological model using an anti-CD3 antibody. During antigenic stimulation we noticed that, except for the proximal p56lck signal, which is triggered early, the signals appear to be delayed and highly sustained. This delay, which likely accounts for the delay observed in TNF-α production, is discussed in terms of the ability of the antigen to crosslink and recruit transducing molecules mostly anchored to lipid rafts. Moreover, we demonstrate that, in contrast to anti-CD3 antibody, IPP does not induce down-modulation of the TcR·CD3 complex, which likely results in the highly sustained signaling and release of high levels of TNF-α.