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Selective differences in macrophage populations and monokine production in resolving pulmonary granuloma and fibrosis
1Department of Pharmacology, Faculty of Medicine, University of Ottawa, Ontario, Canada.
Abstract:
Alveolar macrophages (AM) and their production of interleukin-1-like activity (IL-1) and macrophage-derived growth factor for fibroblasts (MDGF) were examined during chronic inflammatory reactions leading to either granuloma formation or fibrosis. Groups of five rats each received, respectively, a single transtracheal injection of xonotlite, attapulgite, short chrysotile 4T30, UICC chrysotile B asbestos, or saline. One month later, such treatments induced either no change (xonotlite), granuloma formation (attapulgite and short chrysotile 4T30), or fibrosis (UICC chrysotile B). By 8 months, however, the granulomatous reactions had resolved or greatly diminished, whereas the fibrosis persisted irreversibly. Parallel examination of cell populations obtained by bronchoalveolar lavage revealed that multinucleated giant macrophages (MGC) were present in lavage fluids of animals with resolving granulomatous reactions but absent in those obtained from animals with lung fibrosis. Evaluation of monokine production by inflammatory macrophages also revealed significant differences. Enhanced production of IL-1-like activity was seen in both types of lung injury, although especially during the early stage (1 month) and decreased thereafter (8 months). By contrast, augmentation of MDGF production was observed in animals with lung fibrosis only and persisted up to 9 months. Taken together, these data indicate that production of selected cytokines, as well as AM differentiation along a given pathway, may modulate the outcome of a chronic inflammatory response.
Insights
Chronic lung inflammation outcomes depend on alveolar macrophage (AM) activity. Fibrosis is linked to macrophage-derived growth factor (MDGF), while granulomas involve interleukin-1-like activity (IL-1).
Area of Science:
- Pulmonary toxicology
- Immunology
- Cell biology
Background:
- Chronic lung inflammation can lead to either granuloma formation or irreversible fibrosis.
- Alveolar macrophages (AMs) play a critical role in modulating inflammatory responses and tissue repair.
- The specific cytokines produced by AMs may determine the ultimate outcome of lung injury.
Purpose of the Study:
- To investigate the role of AMs and their cytokine production in chronic inflammatory reactions leading to granuloma or fibrosis.
- To compare the production of interleukin-1-like activity (IL-1) and macrophage-derived growth factor for fibroblasts (MDGF) by AMs in different inflammatory models.
- To determine if AM differentiation pathways influence the resolution or persistence of lung injury.
Main Methods:
- Rats were intratracheally instilled with various asbestos fibers (xonotlite, attapulgite, chrysotile) or saline.
- Bronchoalveolar lavage was performed at 1 and 8 months post-instillation to collect inflammatory cells.
- Cytokine production (IL-1-like activity and MDGF) by macrophages was evaluated.
- Cell populations, including multinucleated giant macrophages (MGC), were analyzed.
Main Results:
- Chrysotile B asbestos induced persistent lung fibrosis, while attapulgite and short chrysotile 4T30 induced transient granulomas.
- IL-1-like activity was elevated in early inflammation but decreased by 8 months in both injury types.
- MDGF production was significantly increased only in fibrotic lungs and persisted for up to 9 months.
- MGC were present in resolving granulomas but absent in fibrotic lungs.
Conclusions:
- AM differentiation and cytokine production profiles dictate the outcome of chronic lung inflammation.
- MDGF appears to be a key mediator in the development and persistence of lung fibrosis.
- IL-1-like activity may be more involved in the early, resolving stages of inflammation.
- These findings highlight distinct roles for AMs in determining fibrotic versus granulomatous lung disease progression.