Primed neutrophils require phosphatidic acid for maximal receptor-activated elastase release

Adenosine reduces reactive oxygen species and interleukin-8 production by Trichomonas vaginalis-stimulated neutrophils

Trichomonas vaginalis is a flagellated protozoan that affects the human urogenital tract causing 276.4 million new infections a year. The parasite elicits a vaginal mucosal infiltration of immune cells, especially neutrophils which are considered to be primarily responsible for cytological change observed at the infection site as well as the major contributor in the inflammatory response against the parasite. Extracellular nucleotides and their nucleosides are signaling compounds involved in several biological processes, including inflammation and immune responses. Once in the extracellular space, the nucleotides and nucleosides can directly activate the purinergic receptors. Herein, we investigated the involvement of purinergic signaling on the production of reactive oxygen species (ROS) and cytokines by T. vaginalis-stimulated neutrophils. Parasites were able to induce an increase in ROS and IL-8 levels while they did not promote IL-6 secretion or neutrophil elastase activity. Adenine and guanine nucleotides or nucleosides were not able to modulate ROS and cytokine production; however, when T. vaginalis-stimulated neutrophils were incubated with adenosine and adenosine deaminase inhibitor, the levels of ROS and IL-8 were significantly reduced. These immunosuppressive effects were probably a response to the higher bioavailability of adenosine found in the supernatant as result of inhibition of enzyme activity. The involvement of P1 receptors was investigated by immunofluorescence and A1 receptor was the most abundant. Our data show that the influence of purinergic signaling, specifically those effects associated with adenosine accumulation, on the modulation of production of proinflammatory mediators by T. vaginalis-stimulated neutrophils contribute to the understanding of immunological aspects of trichomoniasis.

Phospholipase D and immune receptor signalling

Immune receptors are coupled to the activation of phosphatidylcholine phospholipase D (PC-PLD) that hydrolyses phosphatidylcholine to generate phosphatidic acid and choline. As these receptors are also coupled to other signalling cascades, it has been difficult to define the precise cell activation events resulting from PLD activation in the absence of specific inhibitors. There is increasing evidence that phosphatidic acid acts as an intracellular signalling molecule regulating release of calcium from intracellular stores, sphingosine kinase and protein kinase C activation and membrane budding. Phosphatidic acid can also be rapidly converted into lysophosphatidic acid, diacylglycerol and arachidonates.