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.

Transforming growth factor beta as a virulence mechanism for Leishmania braziliensis

Transforming growth factor beta (TGF-beta) 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-beta in the pathogenesis of infection with this parasite. Recombinant TGF-beta added to cultures of murine peritoneal macrophages led to increased intracellular L. braziliensis replication, whereas addition of neutralizing anti-TGF-beta monoclonal antibody decreased levels of infection. Macrophages infected with L. braziliensis produced biologically active TGF-beta, with a direct correlation between amounts of TGF-beta induced by two parasite isolates and their relative virulence. In vivo, treatment with recombinant TGF-beta 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-beta is able to alter the course of in vitro and in vivo infections with L. braziliensis, the latter being characterized by an increase in interleukin 10, an important Th2 helper-T-cell cytokine.

Toxoplasma gondii stimulates the release of 13- and 9-hydroxyoctadecadienoic acids by human platelets

We have recently demonstrated a novel cytotoxic effect of human platelets against Toxoplasma gondii and a role for thromboxane (TX) in this process (Yong et al., 1991). We now report on the spectrum of lipid mediators released by human platelets after interaction with T. gondii. In addition to TXB2, human platelets after incubation with T. gondii for 90 min released 12-hydroxyheptadecatrienoic acid (12-HHT), 12-hydroxyeicosatetraenoic acid (12-HETE), and an unidentified peak (UVmax 234 nm) as determined by reverse-phase high-performance liquid chromatography. Thermospray-liquid chromatography/mass spectrometry analysis and straight-phase HPLC identified the unknown peak as a mixture of 13-hydroxyoctadecadienoic acid (HODE) and 9-HODE. Radiolabeling studies with [14C]linoleic acid indicated that the platelets were the cellular source of the octadecanoids with 13-HODE (87.7%) greater than 9-HODE (12.3%). Inhibitor studies with indomethacin indicated that 13-HODE was a lipoxygenase product and 9-HODE was a cyclooxygenase product of linoleic acid. Thus, Toxoplasma-stimulated platelets release oxygenated products of both arachidonic acid and linoleic acid which may be important in the host response to T. gondii infection.

Human platelet-mediated cytotoxicity against Toxoplasma gondii: role of thromboxane

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.

Differential antimicrobial activity of human mononuclear phagocytes against the human biovars of Chlamydia trachomatis

The antimicrobial activities of human mononuclear phagocytes against Chlamydia trachomatis were investigated. Phagocytes cultured for 7 days or less were efficiently microbicidal. Almost complete inactivation of organisms from both human biovars was observed after 48 hr of incubation. However, organisms from the lymphogranuloma venereum (LGV) biovar survived in mononuclear phagocytes infected after 8 days or more in culture, whereas those from the trachoma biovar continued to be killed by such cells. Phagocytes cultured as long as 21 days killed the trachoma organisms with the same effectiveness as those cultured for 7 days or less. An ultrastructural study of inoculated phagocytes illustrated phagolysosomal fusion with degradation of organisms from either biovar in phagocytes which had been cultured for 24 hr before infection. Phagolysosomal fusion was not observed in cells which had been cultured for 8 days or more and then infected with LGV. The addition of interferon-gamma to these macrophages partially restored the phagocytes' microbicidal activity for LGV. Furthermore, a synergistic effect was observed when eosinophil peroxidase was added with interferon. Specific antibody failed to neutralize the infectivity of LGV organisms in 8-day or older mononuclear phagocytes. The findings may reflect the differences in disease syndromes between the two biovars, with the trachoma biovar causing more peripheral diseases and the LGV biovar causing a more systemic disease, with lymph node involvement as its main syndrome.

Differential antimicrobial activity of human mononuclear phagocytes against the human biovars of Chlamydia trachomatis

The antimicrobial activities of human mononuclear phagocytes against Chlamydia trachomatis were investigated. Phagocytes cultured for 7 days or less were efficiently microbicidal. Almost complete inactivation of organisms from both human biovars was observed after 48 hr of incubation. However, organisms from the lymphogranuloma venereum (LGV) biovar survived in mononuclear phagocytes infected after 8 days or more in culture, whereas those from the trachoma biovar continued to be killed by such cells. Phagocytes cultured as long as 21 days killed the trachoma organisms with the same effectiveness as those cultured for 7 days or less. An ultrastructural study of inoculated phagocytes illustrated phagolysosomal fusion with degradation of organisms from either biovar in phagocytes which had been cultured for 24 hr before infection. Phagolysosomal fusion was not observed in cells which had been cultured for 8 days or more and then infected with LGV. The addition of interferon-gamma to these macrophages partially restored the phagocytes' microbicidal activity for LGV. Furthermore, a synergistic effect was observed when eosinophil peroxidase was added with interferon. Specific antibody failed to neutralize the infectivity of LGV organisms in 8-day or older mononuclear phagocytes. The findings may reflect the differences in disease syndromes between the two biovars, with the trachoma biovar causing more peripheral diseases and the LGV biovar causing a more systemic disease, with lymph node involvement as its main syndrome.

Degradation of Chlamydia trachomatis in human polymorphonuclear leukocytes: an ultrastructural study of peroxidase-positive phagolysosomes

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.

Toxic effect of human polymorphonuclear leukocytes on Chlamydia trachomatis

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-H2O2-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 activation 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.

Reticulate bodies as single antigen in Chlamydia trachomatis serology with microimmunofluorescence

Formalin-fixed, purified reticulate bodies (RB) of Chlamydia trachomatis immunotype C/TW-3/OT were used as a serological test antigen in the microimmunofluorescence test. The sensitivity and specificity of the RB antigen were compared to elementary bodies (EB) used as antigens in the detection of C. trachomatis antibodies in human sera by microimmunofluorescence. RB reacted with all known C. trachomatis immunotypes with the same sensitivity as the homotypic EB. In routine serology with sera and endocervical secretions, the RB antigen had a sensitivity similar to that of the EB in detecting serum antibodies, endocervical secretion antibodies, and antibodies of immunoglobulin M and G classes. No false-positive reactions were detected with control sera. All positive reactions showed type-specific antibodies against an EB immunotype. RB seemed to demonstrate chlamydial group reactivity; sera from 10 psittacosis patients diagnosed clinically and serologically by complement fixation showed five positive, three equivocal, and two negative reactions. By immunofluorescence, RB appeared as distinct rings demonstrating uniform peripheral surface fluorescence at their rims. The EB appeared as pinpoint-sized dots. C/TW-3/OT RB used as a single test anitgen should provide a simple and sensitive serological assay for the detection of C. trachomatis antibody.