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Pulmonary intravascular macrophages metabolize arachidonic acid in vitro. Comparison with alveolar macrophages
T A Bertram1, L H Overby, R Danilowicz
1Laboratory of Pulmonary Pathobiology, National Institute of Environmental Health Sciences, Research Triangle Park, North Carolina 27709.
Abstract:
Pulmonary intravascular macrophages are a recently identified component of the pulmonary mononuclear phagocyte system. It has been shown that alveolar macrophages are capable of metabolizing arachidonic acid (AA) to its biologically active inflammatory metabolites via the lipoxygenase and cyclooxygenase pathways. In this study, we have compared the ability of swine intravascular macrophages and alveolar macrophages to metabolize AA in vitro. Alveolar macrophages attached to a plastic substrate produced at least five identified AA metabolites including prostaglandin (PG)F2 alpha, hydroxyheptadecatrienoic acid (HHT), 5-hydroxyeicosatetraenoic acid (HETE), 12-HETE, and 15-HETE. In contrast, adherent intravascular macrophages produced eight identified metabolites including thromboxane (TX)B2, PGF2 alpha, PGD2, PGE2, HHT, 5-HETE, 12-HETE, and 15-HETE. The major lipoxygenase metabolite produced by both macrophage types was 5-HETE. The major cyclooxygenase metabolite produced by alveolar macrophages was PGF2 alpha, whereas the major metabolite produced by intravascular macrophages was HHT. Both macrophage populations treated with calcium ionophore (A23187) exhibited increased production of PGs, TXB2, leukotriene (LT)B4, 5-HETE, 12-HETE, and 15-HETE, but the most striking increase occurred in metabolism through the lipoxygenase pathway. The major lipoxygenase metabolite generated by ionophore-stimulated macrophages was 5-HETE, and in intravascular macrophages 12-HETE was also produced. Preincubation of macrophages with indomethacin and nordihydroguaiaretic acid attenuated the yield of cyclooxygenase metabolites and lipoxygenase metabolites, respectively. Studies of leukotriene formation demonstrated that both macrophage types produce LTC4 and LTB4 from the leukotriene precursor LTA4. Thus, we show that the pulmonary intravascular macrophage is capable of metabolizing AA and LTA4 to their inflammatory and vasoactive metabolites by the cyclooxygenase and lipoxygenase pathways.(ABSTRACT TRUNCATED AT 250 WORDS)
Insights
Pulmonary intravascular macrophages metabolize arachidonic acid (AA) differently than alveolar macrophages, producing distinct inflammatory mediators. This study highlights their varied roles in the pulmonary mononuclear phagocyte system.
Area of Science:
- Immunology
- Cell Biology
- Biochemistry
Background:
- Pulmonary intravascular macrophages (PIMs) are a recently identified component of the mononuclear phagocyte system.
- Alveolar macrophages (AMs) metabolize arachidonic acid (AA) into inflammatory mediators via lipoxygenase and cyclooxygenase pathways.
Purpose of the Study:
- To compare the in vitro arachidonic acid (AA) metabolism capabilities of swine pulmonary intravascular macrophages (PIMs) and alveolar macrophages (AMs).
- To identify the specific AA metabolites produced by each macrophage type and their response to stimulation.
Main Methods:
- In vitro incubation of isolated swine PIMs and AMs.
- Metabolite analysis of arachidonic acid (AA) using lipoxygenase and cyclooxygenase pathways.
- Stimulation with calcium ionophore (A23187) and preincubation with pathway inhibitors (indomethacin, nordihydroguaiaretic acid).
Main Results:
- PIMs produced eight identified AA metabolites, including thromboxane (TX)B2, prostaglandins (PGs), and hydroxyeicosatetraenoic acids (HETEs).
- AMs produced five identified AA metabolites, with PGF2 alpha as the major cyclooxygenase product and 5-HETE as the major lipoxygenase product.
- Ionophore stimulation significantly increased lipoxygenase pathway metabolites in both PIMs and AMs, with PIMs showing increased 12-HETE production.
Conclusions:
- Pulmonary intravascular macrophages (PIMs) exhibit distinct arachidonic acid (AA) metabolism compared to alveolar macrophages (AMs).
- Both PIMs and AMs metabolize AA and leukotriene precursor LTA4 into inflammatory and vasoactive mediators via cyclooxygenase and lipoxygenase pathways.
- These findings elucidate the specialized roles of PIMs within the pulmonary immune system.