Cytotoxic activity of 13-hydroxyoctadecadienoic acid against Toxoplasma gondii

Platelets as immune cells in infectious diseases

Platelets have been shown to cover a broad range of functions. Besides their role in hemostasis, they have immunological functions and thus participate in the interaction between pathogens and host defense. Platelets have a broad repertoire of receptor molecules that enable them to sense invading pathogens and infection-induced inflammation. Consequently, platelets exert antimicrobial effector mechanisms, but also initiate an intense crosstalk with other arms of the innate and adaptive immunity, including neutrophils, monocytes/macrophages, dendritic cells, B cells and T cells. There is a fragile balance between beneficial antimicrobial effects and detrimental reactions that contribute to the pathogenesis, and many pathogens have developed mechanisms to influence these two outcomes. This review aims to highlight aspects of the interaction strategies between platelets and pathogenic bacteria, viruses, fungi and parasites, in addition to the subsequent networking between platelets and other immune cells, and the relevance of these processes for the pathogenesis of infections.

Peroxisome proliferator-activated receptor (PPAR): balance for survival in parasitic infections

Parasitic infections induce a magnitude of host responses. At the opposite ends of the spectrum are those that ensure the host's needs to eliminate the invaders and to minimize damage to its own tissues. This review analyzes how parasites would manipulate immunity by activating the immunosuppressive nuclear factor, peroxisome proliferator-activated receptors (PPARs) with type 2 cytokines and free fatty acids from arachidonic acid metabolism. PPARs limit the action of type 1 immunity, in which classically activated macrophages act through the production of proinflammatory signals, to spare the parasites. They also favor the development of alternately activated macrophages which control inflammation so the host would not be destroyed. Possibly, the nuclear factors hold a pivotal role in the establishment of chronic infection by delicately balancing the pro- and anti-inflammatory signaling mechanisms and their ligands may be used as combination therapeutics to limit host pathology.

Production of eicosanoids and other oxylipins by pathogenic eukaryotic microbes

Oxylipins are oxygenated metabolites of fatty acids. Eicosanoids are a subset of oxylipins and include the prostaglandins and leukotrienes, which are potent regulators of host immune responses. Host cells are one source of eicosanoids and oxylipins during infection; however, another potential source of eicosanoids is the pathogen itself. A broad range of pathogenic fungi, protozoa, and helminths produce eicosanoids and other oxylipins by novel synthesis pathways. Why do these organisms produce oxylipins? Accumulating data suggest that phase change and differentiation in these organisms are controlled by oxylipins, including prostaglandins and lipoxygenase products. The precise role of pathogen-derived eicosanoids in pathogenesis remains to be determined, but the potential link between pathogen eicosanoids and the development of TH2 responses in the host is intriguing. Mammalian prostaglandins and leukotrienes have been studied extensively, and these molecules can modulate Th1 versus Th2 immune responses, chemokine production, phagocytosis, lymphocyte proliferation, and leukocyte chemotaxis. Thus, eicosanoids and oxylipins (host or microbe) may be mediators of a direct host-pathogen "cross-talk" that promotes chronic infection and hypersensitivity disease, common features of infection by eukaryotic pathogens.

Lipids of three microsporidian species and multivariate analysis of the host-parasite relationship

Sporal lipids of 3 microsporidia, Encephalitozoon cuniculi from mammals and Glugea atherinae and Spraguea lophii from fishes, were investigated. High phospholipid levels were found (54.8-64.5% of total lipids), which is in agreement with the presence of highly developed internal membranes in microsporidian spores. Sphingomyelin was not detected in G. atherinae. Triglycerides (less than 10% of total lipids), cholesterol, and free fatty acids were identified in all species. Analysis of fatty acids from the phospholipid fraction revealed the predominance of docosahexaenoic acid (30-40% of total phospholipid fatty acids) in G. atherinae and S. lophii and oleic acid (25.8% of total phospholipid fatty acids) in E. cuniculi. The 3 microsporidia possessed a significant amount of branched-chain fatty acids (iso and anteiso forms) not found in the hosts, supporting the existence of some parasite-specific metabolic steps for these fatty acids. On the basis of phospholipid fatty acid profiles, host-parasite relationships were investigated through correspondence factorial analysis. It shows 3 distinct clusters with the first corresponding to fishes, the second to fish parasites, and the third to E. cuniculi and its host cell. These data suggest that the mammal microsporidia developing within parasitophorous vacuoles are more dependent on host cells than the fish microsporidia that induce cystlike structures.

Toxoplasma gondii alters eicosanoid release by human mononuclear phagocytes: role of leukotrienes in interferon gamma-induced antitoxoplasma activity

Toxoplasma gondii tachyzoites markedly alter the profile of eicosanoids released by human mononuclear phagocytes. Freshly isolated, 2-h adherent human monocytes release both cyclooxygenase (e.g., thromboxane [TX] B2, prostaglandin [PG] E2) and 5-lipoxygenase (e.g., leukotriene [LT] B4, LTC4) products of arachidonic acid metabolism after stimulation by the calcium ionophore A23187 or ingestion of opsonized zymosan particles or heat-killed T. gondii. However, after incubation with viable T. gondii, normal and chronic granulomatous disease monocytes release only the cyclooxygenase products TXB2 and PGE2 and fail to form LTB4, LTC4, or other 5-lipoxygenase products. Monocytes maintained in culture for 5 d lose this capacity to release TXB2 and PGE2 after incubation with T. gondii. T. gondii significantly inhibit calcium ionophore A23187-induced LTB4 release by monocyte-derived macrophages; heat-killed organisms do not affect this calcium ionophore A23187-induced release of LTB4. T. gondii-induced inhibition of LTB4 release by calcium ionophore A23187-stimulated monocyte-derived macrophage is reversed by interferon (IFN)-gamma treatment of the monolayers. LTB4 induced extensive damage to the cellular membranes and cytoplasmic contents of the organisms as observed by transmission electron microscopy. Exogenous LTB4 (10(-6) M) induced intracellular killing of ingested T. gondii by non-IFN-gamma-treated monocyte-derived macrophages. IFN-gamma-induced antitoxoplasma activity in monocyte-derived macrophages was inhibited by the selective 5-lipoxygenase inhibitor zileuton but not by the cyclooxygenase inhibitor indomethacin. These findings suggest a novel role for 5-lipoxygenase arachidonic acid products in human macrophage IFN-gamma-induced antitoxoplasma activity.

Immunity to Toxoplasma gondii

Recent advances in our understanding of the immunological mechanisms involved during infection with Toxoplasma gondii include evidence for the role of different subsets of lymphocytes and cytokines in acute infection as well as in reactivation of chronic infection. The mechanisms of presentation of T. gondii antigen have been clarified recently, and animal models of toxoplasmosis that mimic disease observed in AIDS patients developed.