Mitochondrial Dysfunction, Depleted Purinergic Signaling, and Defective T Cell Vigilance and Immune Defense.

T cell suppression in sepsis is a well-known phenomenon; however, the underlying mechanisms are not fully understood. Previous studies have shown that T cell stimulation up-regulates mitochondrial adenosine triphosphate (ATP) production to fuel purinergic signaling mechanisms necessary for adequate T cell responses. Here we show that basal mitochondrial ATP production, ATP release, and stimulation of P2X1 receptors represent a standby purinergic signaling mechanism that is necessary for antigen recognition. Inhibition of this process impairs T cell vigilance and the ability of T cells to trigger T cell activation, up-regulate mitochondrial ATP production, and stimulate P2X4 and P2X7 receptors that elicit interleukin 2 production and T cell proliferation. T cells of patients with sepsis lack this standby purinergic signaling system owing to defects in mitochondrial function, ATP release, and calcium signaling. These defects impair antigen recognition and T cell function and are correlated with sepsis severity. Pharmacological targeting of these defects may improve T cell function and reduce the risk of sepsis.