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Expression and regulation of human alveolar macrophage-derived interleukin-1 receptor antagonist
S A Moore1, R M Strieter, M W Rolfe
1Department of Pathology, University of Michigan Medical School, Ann Arbor 48109-0602.
Abstract:
The alveolar macrophage (AM) is the sentinel immune cell of the distal airspace of the lung. These mononuclear phagocytic cells represent the major host defense against inhaled environmental agents. When activated, the AM has the capacity to release reactive oxygen and arachidonic acid metabolites and produce a number of cytokines, such as interleukin-1 (IL-1). This latter cytokine has pleiotropic effects on a variety of cells and has been implicated as one of the preeminent mediators of acute inflammation. Recently, an IL-1 receptor antagonist (IRAP) has been isolated, purified, and cloned from peripheral blood monocytes (PBM) stimulated with either adherent IgG (adhIgG) lipopolysaccharide (LPS), or phorbol myristate acetate. IRAP acts as a true receptor antagonist without agonist activity. We postulated that the AM would be a significant cellular source of IRAP from the lung. To test this hypothesis, normal human AM were immediately isolated or stimulated in a dose-dependent fashion with either LPS or adhIgG. For comparison, PBM were also isolated and treated in a similar manner. PBM expressed steady-state IRAP mRNA by Northern blot analysis only in response to LPS or adhIgG. In contrast, AM were found to express significant levels of antigenic IRAP by Western blot analysis, immunostaining, and specific ELISA, and express steady-state levels of IRAP mRNA under unstimulated culture conditions. Moreover, LPS or adhIgG failed to induce AM-derived IRAP antigen generation over unstimulated control.(ABSTRACT TRUNCATED AT 250 WORDS)
Insights
Alveolar macrophages (AMs) are key lung immune cells. Unlike peripheral blood monocytes, AMs naturally produce IL-1 receptor antagonist (IRAP) without external stimulation, identifying them as a primary lung source.
Area of Science:
- Immunology
- Pulmonology
- Cell Biology
Background:
- Alveolar macrophages (AMs) are crucial lung immune cells defending against inhaled agents.
- Activated AMs release inflammatory mediators like interleukin-1 (IL-1).
- IL-1 receptor antagonist (IRAP) modulates inflammatory responses.
Purpose of the Study:
- To investigate if AMs are a significant source of IRAP in the lung.
- To compare IRAP production in AMs versus peripheral blood monocytes (PBMs).
Main Methods:
- Isolation and culture of human AMs and PBMs.
- Stimulation with lipopolysaccharide (LPS) or adherent IgG (adhIgG).
- Analysis of IRAP expression using Western blot, immunostaining, ELISA, and Northern blot for mRNA.
Main Results:
- PBMs required stimulation (LPS or adhIgG) to express IRAP mRNA.
- AMs expressed significant levels of IRAP protein and mRNA even without stimulation.
- Further stimulation of AMs with LPS or adhIgG did not increase IRAP production.
Conclusions:
- Human AMs are a significant source of IRAP in the lung.
- AMs constitutively produce IRAP, unlike PBMs which require activation.
- This suggests a unique role for AMs in regulating lung inflammation via IRAP production.