Activation of the P2X(7) receptor triggers the elimination of Toxoplasma gondii tachyzoites from infected macrophages.

Toxoplasmosis is caused by the protozoan parasite Toxoplasma gondii, which is widespread throughout the world. After active penetration, the parasite is enclosed within a parasitophorous vacuole and survives in the host cell by avoiding, among other mechanisms, lysosomal degradation. A large number of studies have demonstrated the importance of ATP signalling via the P2X(7) receptor, as a component of the inflammatory response against intracellular pathogens. Here we evaluate the effects of extracellular ATP on T. gondii infection of macrophages. ATP treatment inhibits the parasite load and the appearance of large vacuoles in the cytoplasm of intracellular parasites. ROS and NO assays showed that only ROS production is involved with the ATP effects. Immunofluorescence showed colocalization of Lamp1 and SAG1 only after ATP treatment, suggesting the formation of phagolysosomes. The involvement of P2X(7) receptors in T. gondii clearance was confirmed by the use of P2X(7) agonists and antagonists, and by infecting macrophages from P2X(7) receptor-deficient mice. We conclude that parasite elimination might occur following P2X(7) signalling and that novel therapies against intracellular pathogens could take advantage of activation of purinergic signalling.

Expression and function of the purinergic receptor P2X7 in patients with pulmonary tuberculosis.

P2X(7) is a channel receptor gated by adenosine triphosphate (ATP) that is involved in the killing of intracellular mycobacteria. To explore further the role of P2X(7) in immunity against Mycobacterium tuberculosis, we studied its expression and function in 19 patients with pulmonary tuberculosis (TB) and 19 healthy contacts. Flow cytometry analysis showed a similar and variable expression of P2X(7) in TB patients and healthy subjects. In contrast, P2X(7) mARN levels were significantly higher in TB patients. When the function of the P2X(7) receptor in peripheral blood mononuclear cells (PBMC) was assessed by the effect of exogenous ATP on apoptosis, the uptake of the fluorescent marker Lucifer yellow or extracellular signal regulated kinase (ERK) phosphorylation, no significant differences were detected in patients and controls. However, mRNA macroarray analysis showed that upon stimulation with ATP, the PBMC from TB patients showed a significant induction of a higher number of cytokine genes (27 of 96), and a lower number of apoptosis genes (20 of 96) compared to healthy controls (17 and 76 genes, respectively). These results suggest that although the PBMC from TB patients do not show apparent abnormalities in the expression of P2X(7), and the intracellular signals generated through it, the pattern of gene expression induced by ATP in these cells is different from that found in healthy contacts. This phenomenon suggests a defective function of P2X(7) in the immune cells from TB patients, a condition that may contribute to the inability of these patients to eliminate the mycobacteria.