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Alteration of leukotriene release by macrophages ingesting Toxoplasma gondii
Abstract:
Mouse resident peritoneal macrophages incubated with ionophore A23187 or opsonized zymosan released leukotrienes (LT) B4 and C4 (LTB4 and LTC4) and LTC4 and LTD4, respectively. In contrast, incubation with Toxoplasma gondii, an obligate intracellular protozoan, led to the formation of 11-, 12-, and 15-hydroxyicosatetraenoic acids (HETEs), together with an unidentified compound, designated compound X. Each of these compounds incorporated [3H]arachidonic acid from the macrophage during phagocytosis of T. gondii. Compound X migrated immediately prior to 15-HETE by reverse-phase HPLC and was distinct from authentic monoHETE, monohydroperoxyicosatetraenoic acid (mono-HPETE), and dihydroxyicosatetraenoic acid (diHETE) standards. The generation of compound X by macrophages correlated with the extent of phagocytosis of T. gondii and with intracellular survival of the organisms. Prior antibody-coating of T. gondii or activation of macrophages, either of which inhibited survival and replication of ingested organisms, was associated with production of LTD4 but not compound X. Killed organisms also stimulated LTD4 release only. Although T. gondii concentrated arachidonic acid, they did not metabolize the compound to identifiable lipoxygenase products. Preincubation of macrophages with the relative lipoxygenase inhibitors nordihydroguaiaretic acid or 5,8,11,14-icosatetraynoic acid inhibited the formation of compound X. The absence of leukotriene production by macrophages ingesting T. gondii may explain the relative lack of a neutrophil inflammatory response in diseases due to obligate intracellular organisms. Alternatively, compound X may have functional activities that might mediate some of the host responses to cellular parasitism.
Insights
Macrophages infected with Toxoplasma gondii produce a novel compound (compound X) instead of typical inflammatory leukotrienes. This may explain reduced neutrophil response in parasitic infections.
Area of Science:
- Immunology
- Cell Biology
- Biochemistry
Background:
- Macrophages are key immune cells involved in host defense.
- Lipid mediators like leukotrienes (LTs) play crucial roles in inflammation.
- Obligate intracellular protozoa like Toxoplasma gondii evade host immune responses.
Purpose of the Study:
- To investigate the lipid mediator production by macrophages during Toxoplasma gondii infection.
- To identify novel metabolites produced during phagocytosis of T. gondii.
- To understand the host-pathogen interaction at the molecular level of lipid metabolism.
Main Methods:
- Incubation of mouse peritoneal macrophages with T. gondii or other stimuli (zymosan, ionophore).
- Analysis of lipid mediators using High-Performance Liquid Chromatography (HPLC).
- Inhibition studies using lipoxygenase inhibitors (nordihydroguaiaretic acid, 5,8,11,14-icosatetraynoic acid).
Main Results:
- Macrophages produced leukotrienes (LTB4, LTC4, LTD4) in response to ionophore or zymosan.
- Infection with T. gondii led to the formation of hydroxyicosatetraenoic acids (HETEs) and a novel compound (compound X).
- Compound X formation correlated with T. gondii phagocytosis and intracellular survival, and was inhibited by lipoxygenase inhibitors.
Conclusions:
- T. gondii infection alters macrophage lipid metabolism, shifting production from leukotrienes to HETEs and compound X.
- The absence of leukotriene production may contribute to the limited neutrophil response observed in T. gondii infections.
- Compound X's functional role in host response to intracellular parasitism requires further investigation.