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Assessment of in vivo attachment/phagocytosis by alveolar macrophages
T Weaver1, C L Hall, D L Kachel
1Division of Pulmonary, Critical Care, and Occupational Medicine, Indiana University School of Medicine, Indianapolis 46202, USA.
Abstract:
Alveolar macrophages (AMs) are recognized as an important first line of cellular host defense within the lung. Although mechanisms underlying AM response to microorganisms or particulates are well characterized in vitro, experimental approaches to the study of AMs in vivo are limited. To circumvent these limitations, a new assay was developed using fluorescently labelled liposomes or Pneumocystis carinii (PC) organisms which were administered intratracheally into mechanically ventilated rats. After 30 min, the lungs were lavaged and the percentage of administered liposomes or PC bound to AMs was determined by quantifying fluorescence. Factors known to enhance attachment/phagocytosis by AMs in vitro were assayed to determine their effect in vivo. For example, vitronectin (VN)-coated liposomes increased attachment from 25.2 +/- 2.4% to 47.2 +/- 3.0% (p < 0.001), while addition of VN increased the binding of PC to AMs from 16.5 +/- 1.7% to 24.5 +/- 2.2% (p < 0.05). Confocal laser microscopy of cells obtained by lavage provided morphologic evidence of attachment/phagocytosis by AMs. This model will permit the quantitative assessment of the interaction of fluorescently labelled liposomes or microorganisms with AMs in the lower respiratory tract of living animals.
Insights
A novel in vivo assay quantifies alveolar macrophage (AM) interactions with lung pathogens. This method uses fluorescently labeled particles in mechanically ventilated rats, enabling new insights into lung defense mechanisms.
Area of Science:
- Pulmonary immunology
- Cellular biology
- Host-pathogen interactions
Background:
- Alveolar macrophages (AMs) are crucial for lung defense against microbes and particles.
- In vitro studies of AMs are well-established, but in vivo experimental approaches are limited.
- Studying AMs in a living organism presents significant experimental challenges.
Purpose of the Study:
- To develop a novel in vivo assay for studying alveolar macrophage (AM) interactions.
- To quantitatively assess the binding and phagocytosis of foreign particles and microorganisms by AMs in the lower respiratory tract.
- To validate the assay's utility by testing factors known to influence AM activity in vitro.
Main Methods:
- Development of an in vivo assay using fluorescently labeled liposomes or Pneumocystis carinii (PC) administered intratracheally into mechanically ventilated rats.
- Lung lavage followed by quantification of fluorescently labeled material bound to AMs.
- Assessment of factors like vitronectin (VN) to enhance AM attachment and phagocytosis in vivo.
- Confocal laser microscopy for morphologic validation of AM-particle/microorganism interactions.
Main Results:
- The assay successfully quantified the percentage of administered liposomes or PC bound to AMs.
- Vitronectin (VN)-coated liposomes significantly increased AM attachment (25.2% to 47.2%).
- Addition of VN enhanced PC binding to AMs (16.5% to 24.5%).
- Confocal microscopy confirmed morphologic evidence of AM attachment and phagocytosis.
Conclusions:
- A new, quantitative in vivo assay allows for the study of alveolar macrophage (AM) interactions in the lower respiratory tract.
- This model overcomes limitations of in vitro studies and permits the assessment of factors influencing AM function in a living animal.
- The assay provides a valuable tool for understanding lung host defense mechanisms against various inhaled substances and pathogens.