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Pulmonary granuloma formation in the rat is partially dependent on monocyte chemoattractant protein 1
C M Flory1, M L Jones, J S Warren
1Department of Pathology, University of Michigan Medical School, Ann Arbor.
Background:
We have examined the role of MCP-1 (monocyte chemoattractant protein 1; also known as monocyte chemotactic and activating factor or the murine JE gene product) in the pathogenesis of glucan-induced granulomatous vasculitis in the rat. While in vitro studies indicate that MCP-1 possesses monocyte chemotactic and activating activities, little is known about its biologic role in pathologic processes. Glucan-induced pulmonary granulomatous vasculitis is an ideal model in which to study the role of MCP-1, because the granulomas develop rapidly and synchronously and are monocyte/macrophage-rich.
Experimental Design:
The purpose of this study was to define the topographic distribution and temporal pattern of MCP-1 expression in the lungs of rats with evolving glucan-induced granulomatous vasculitis and to determine the effect of neutralization of MCP-1 activity on granuloma formation. Glucan-induced pulmonary granulomatous vasculitis was induced in rats by the intravenous infusion of yeast cell wall glucan. At the indicated time points after glucan infusion, rats were sacrificed and the lungs processed for Northern, immunohistochemical and in situ hybridization analyses of MCP-1 production. Morphometric analysis was used to quantify the effect of neutralization of MCP-1 activity on granuloma formation.
Results:
Granuloma formation was accompanied by a biphasic increase in steady-state whole lung MCP-1 mRNA levels that peaked at 1 and 6 to 24 hours. In situ hybridization and immunohistochemical analyses revealed that components of the bronchial and vascular walls are responsible for the early rise (1 hour) in MCP-1 mRNA and protein expression, whereas granuloma-associated alveolar macrophages are the predominant source of MCP-1 later (6 to 24 hours) in the evolution of these lesions. Intravenous infusion and/or intratracheal instillation of neutralizing concentrations of anti-rat MCP-1 antibody raised against recombinant rat MCP-1 resulted in a dramatic decrease in the number and size of glucan-induced granulomas as well as in the numbers of mononuclear phagocytes retrieved in bronchoalveolar lavage fluid.
Conclusions:
These studies demonstrate that glucan-induced granulomatous vasculitis is accompanied by increased local expression of MCP-1 mRNA and protein, that there is a coordinated production of MCP-1 by different cell types within the lung during evolving glucan-induced pulmonary vasculitis, and that MCP-1 plays a requisite role in pulmonary granuloma formation.
Insights
Monocyte chemoattractant protein 1 (MCP-1) is crucial in forming granulomas during glucan-induced vasculitis. Neutralizing MCP-1 significantly reduces granuloma development and associated inflammatory cells in the lungs.
Area of Science:
- Immunology
- Pathology
- Respiratory Medicine
Background:
- Monocyte chemoattractant protein 1 (MCP-1), also known as monocyte chemotactic and activating factor, plays a role in monocyte recruitment.
- Its specific function in pathological processes like glucan-induced granulomatous vasculitis remains largely uncharacterized.
- Glucan-induced pulmonary granulomatous vasculitis is a suitable model for studying MCP-1 due to its rapid, synchronous, and monocyte/macrophage-rich granuloma formation.
Purpose of the Study:
- To delineate the temporal and spatial expression patterns of MCP-1 in the lungs during the development of glucan-induced granulomatous vasculitis.
- To investigate the impact of MCP-1 neutralization on the formation of these granulomas.
Main Methods:
- Rats were induced with glucan-induced pulmonary granulomatous vasculitis via intravenous infusion.
- MCP-1 expression was analyzed using Northern, immunohistochemical, and in situ hybridization techniques at various time points.
- Morphometric analysis quantified the effect of anti-rat MCP-1 antibody administration on granuloma size and cellularity.
Main Results:
- A biphasic increase in MCP-1 mRNA levels was observed, peaking at 1 hour and 6-24 hours post-glucan infusion.
- Early MCP-1 expression originated from bronchial and vascular walls, while later expression was predominantly from alveolar macrophages within granulomas.
- Neutralization of MCP-1 activity led to a significant reduction in granuloma number and size, and decreased mononuclear phagocytes in bronchoalveolar lavage fluid.
Conclusions:
- Glucan-induced granulomatous vasculitis is associated with elevated local MCP-1 mRNA and protein expression.
- Distinct lung cell types exhibit coordinated MCP-1 production during the progression of this vasculitis.
- MCP-1 is essential for the formation of pulmonary granulomas in this model.