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Effects of endotoxin on expression of VLA integrins by human bronchoalveolar lavage macrophages
Y H Kang1, C H Lee, S E Brummel
1Septic Shock Research Program, Naval Medical Research Institute, Bethesda, MD 20889-5607, USA.
Abstract:
Endotoxin (lipopolysaccharide, LPS) is known to induce inflammatory responses, such as monocyte/macrophage adherence, migration, and accumulation. Recruitment and accumulation of macrophages during infection and inflammation are regulated by integrin-mediated cell-extracellular matrix interactions. In the present report, we studied the effects of LPS on the expression of VLA-5 (alpha 5 beta 1), VLA-3 (alpha 3 beta 1), and VLA-2 (alpha 2 beta 1) integrins and fibronectin (FN) by human alveolar macrophages in an attempt to understand the mechanism by which LPS regulates macrophage adhesion to matrix proteins. Bronchoalveolar lavage macrophages were treated with varying concentrations of Escherichia coli LPS for different times and evaluated for expression of the integrins and FN by immunofluorescence, immunoelectron microscopy, autoradiography, and radioimmunoassay. Immunofluorescent and immunoelectron microscopic observations showed that VLA integrins were constitutively expressed on the cell surface and concentrated on the microvilli and pseudopodia of the macrophages. The effects of LPS on expression of the integrins were dose and time related. VLA-5 expression was increased after 30 min of stimulation by LPS, suggesting that LPS may induce rapid secretion of the integrin. However, incubations with LPS longer than 30 min decreased VLA-5 expression in a dose-dependent pattern. LPS also caused dose-related decreases in the expression of VLA-3 and VLA-2 integrins and increases of intracellular FN 24 h after stimulation. The results suggest that a prolonged exposure to LPS may impede VLA integrin-mediated migration and result in local accumulation of macrophages in the lung.
Insights
Endotoxin (lipopolysaccharide, LPS) alters macrophage integrin expression. Prolonged LPS exposure decreases VLA integrins, potentially hindering macrophage migration and causing lung accumulation.
Area of Science:
- Immunology
- Cell Biology
Background:
- Endotoxin (lipopolysaccharide, LPS) triggers inflammatory responses, including macrophage recruitment and accumulation.
- Integrin-mediated interactions with the extracellular matrix regulate macrophage migration during inflammation.
Purpose of the Study:
- To investigate the effects of LPS on VLA integrin and fibronectin expression in human alveolar macrophages.
- To elucidate the mechanism by which LPS influences macrophage adhesion to matrix proteins.
Main Methods:
- Human alveolar macrophages were treated with varying concentrations and durations of Escherichia coli LPS.
- Integrin and fibronectin expression was assessed using immunofluorescence, immunoelectron microscopy, autoradiography, and radioimmunoassay.
Main Results:
- VLA integrins (VLA-5, VLA-3, VLA-2) are constitutively expressed on macrophages.
- Short-term LPS exposure increased VLA-5 expression, while prolonged exposure decreased VLA-5, VLA-3, and VLA-2 expression.
- LPS also increased intracellular fibronectin levels after 24 hours of stimulation.
Conclusions:
- LPS modulates VLA integrin expression in a dose- and time-dependent manner.
- Prolonged LPS exposure may impair VLA integrin-mediated macrophage migration.
- This impairment could contribute to local macrophage accumulation in the lung during inflammatory conditions.