Isopentenyl pyrophosphate, a mycobacterial non-peptidic antigen, triggers delayed and highly sustained signaling in human gamma delta T lymphocytes without inducing down-modulation of T cell antigen receptor

The V gamma 9V delta2 T cell subset, which represents up to 90% of the circ ulating gamma delta T cells in humans, was shown to be activated, via the T cell receptor (TcR), by non-peptidic phosphorylated small organic molecule s. These phosphoantigens, which are not presented by professional antigen-p resenting cells, induce production of high amounts of interferon-gamma and tumor necrosis factor (TNF-alpha). 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 V gamma 9V delta2 T ce lls, and compare these to signals induced by the non-physiological model us ing an anti-CD3 antibody. During antigenic stimulation we noticed that, exc ept for the proximal p56(lck) signal, which is triggered early, the signals appear to be delayed and highly sustained. This delay, which likely accoun ts for the delay observed in TNF-alpha production, is discussed in terms of the ability of the antigen to cross-link 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 c omplex, which likely results in the highly sustained signaling and release of high levels of TNF-alpha.