Transforming growth factor I8 (TGF-1) has potent down-regulating effects on macrophages and is thus capable of influencing the fate of intramacrophage parasites, including leishmanias. We report the development of a mouse model for the study of the human pathogen Leishmania braziliensis and demonstrate, both in vitro and in vivo, a key regulatory role for TGF-fi in the pathogenesis of infection with this parasite. Recombinant TGF-fi added to cultures of murine peritoneal macrophages led to increased intracellular L. braziliensis replication, whereas addition of neutralizing anti-TGF-fi monoclonal antibody decreased levels of infection.Macrophages infected with L. braziliensis produced biologically active TGF-(3, with a direct correlation between amounts of TGF-13 induced by two parasite isolates and their relative virulence. In vivo, treatment with recombinant TGF-fi rendered avirulent parasites virulent and activated latent L. braziliensis infection. Activation of parasite replication was observed in mice which had been infected with L. braziliensis 15 weeks previously but had not developed lesions or had healed lesions, depending on the parasite isolate used to infect the mice. The exacerbation of L. braziliensis infection in vivo was associated with an increase of interleukin 10 mRNA in the draining lymph node. These results demonstrate that TGF-13 is able to alter the course of in vitro and in vivo infections with L.

Human platelets, in the absence of antibody, are cytotoxic to tachyzoites of Toxoplasma gondii as determined by vital staining, transmission electron microscopy, and the failure of Toxoplasma to survive and replicate in mice after in vitro interaction of the organisms with platelets. Platelet to T. gondii ratios as low as 1:3 were toxic to the organisms with direct cell-cell contact essential for platelet-mediated cytotoxicity. Adherence of platelets to T. gondii and disruption of surface membranes and cytoplasmic contents of the organisms were observed ultrastructurally. Reactive oxygen species were not implicated in the platelet-mediated toxicity. The interaction of T. gondii with platelets resulted in a marked increase in thromboxane B2 (TXB2) production compared with that by unstimulated platelets. The cyclooxygenase inhibitors acetylsalicylic acid and indomethacin inhibited platelet-mediated cytolytic activity as did the selective TXA2 synthetase inhibitor dazmegrel, indicating a role for thromboxane in the platelet-induced cytotoxicity. Further, toxoplasmacidal activity was retained in the TXA2 synthetase-containing microsomal fractions of platelets disrupted by freezing and thawing; cytolytic activity was absent in microsome-depleted platelet supernatant fractions. Both the TXA2-generating platelet microsome system and a stable TXA2 analogue induced damage to the cellular membranes of the Toxoplasma as noted by transmission electron microscopy. These findings suggest that platelets may play a role in the host defense against Toxoplasma and that release of thromboxane may be important in this cytolytic process.

SummaryToxoflasma 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 5-1ipoxygenase (e.g., leukotriene [LT] ]]4, 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 5-1ipoxy-genase 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 macrophages is reversed by interferon (IFN)-3' 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-q,-treated monocyte-derived macrophages. IFN-y-induced antitoxoplasma activity in monocyte-derived macrophages was inhibited by the selective 5-1ipoxygenase inhibitor zileuton but not by the cyclooxygenase inhibitor indomethacin. These findings suggest a novel role for 5-1ipoxygenase arachidonic acid products in human macrophage IFN-3,-induced antitoxoplasma activity.H uman monocytes, but not monocyte-derived macrophages, are cytotoxic to Toxoplasma gondii, an obligate intracellular protozoal parasite (1-3). Monocytes possess a granule peroxidase identical to myeloperoxidase (MPO) 1 of neutrophils and respond to stimulation with a respiratory burst leading to the formation of superoxide anion (Of) and hydrogen peroxide (H202) (4). Monocytes derived from peripheral blood and maintained as adherent cells in culture undergo a variety of biochemical and morphologic changes and differentiate into cells resembling tissue macrophages (5-7). During this transformation in culture, there is a progressive loss of the granule peroxidase (5, 8); after an initial rise at day 3, H202 release also greatly decreases (9). Treatment of 1 Abbreviations used in this paper: CGD, chronic granulomatous disease; HETE, hydroxyeicosatetraenoic acid; IFA, indirect fluorescence antibody; LT, leukotriene; MPO, myeloperoxidase; TX, thromboxane. monocyte-derived macrophages with IFN-3, results in their activation with a concomitant increase in H202 generation when stimulated (7,10).The capacity to generate oxygen radicals and the presence of MPO has been correlated with the antiprotozoal activity of phagocytes (2,11,12). Neutrophils and freshly isolated peroxi...

The effect of human polymorphonuclear leukocytes (PMNs) on Chlamydia trachomatis was studied. Both trachoma (B[TW-5/OT) and lymphogranuloma venereum (L2/434/Bu) biotypes were rapidly inactivated by exposure to human PMNs. A decrease of 3 to 3.5 logs in viable count was observed after 60 min of incubation at a chlamydia-to-PMN ratio of 1:10. Both chlamydial biotypes were also rapidly inactivated by the cell-free myeloperoxidase-H202-halide system. A decrease in infectivity titer of 4 to 5 logs for TW-5 and complete inactivation of 434 were seen after 30 min of incubation. The microbicidal effect was prevented by the deletion of each component of the system or by the addition of the peroxidase inhibitors cyanide or azide. PMNs from myeloperoxidase-deficient patients inactivated chlamydiae normally, whereas PMNs from patients with chronic granulomatous disease, although strongly chlamydicidal, were less effective than normal PMNs in the inactivation of TW-5 (2-log drop in viable organisms versus a 3 to 3.5-log drop). The chlamydicidal activity of PMNs from patients with chronic granulomatous disease and normal PMNs were comparable against the 434 biotype. These studies suggest that the myeloperoxidase system, or indeed oxygen-dependent antimicrobial systems, are not essential for the chlamydicidal activity of PMNs.

We have previously shown that human polymorphonuclear leukocytes (PMNs) killed organisms belonging to both human biovars of Chlamydia trachomatis. However, the mechanism of destruction was still unclear. We therefore conducted an ultrastructural and cytochemical study to investigate the mechanism of chlamydial degradation. PMNs were inoculated with the trachoma serovar B (B/TW-5/OT) or with the lymphogranuloma venereum serovar L2 (L2/434/Bu) for 15, 30, 60, or 120 min and then fixed and processed for transmission electron microscopy. Diaminobenzidine, a cytochemical marker, was used to demonstrate the localization of intracellular peroxidase. Ultrastructural evidence is presented showing the progressive degradation of chlamydiae over a 2-h period within peroxidase-positive phagolysosomes. Pretreatment of organisms with normal or immune serum was not required for the process of degradation.