ASSESSMENT OF IN-VIVO ATTACHMENT PHAGOCYTOSIS BY ALVEOLAR MACROPHAGES/

Alveolar macrophages (AMs) are recognized as an important first line o f cellular host defense within the lung. Although mechanisms underlyin g AM response to microoganisms or particulates are well characterized in vitro, experimental approaches to the study of AMs in vivo are limi ted. To circumvent these limitations, a new assay was developed using fluorescently labelled liposomes or Pneumocystis carinii (PC) organism s which were administered intratracheally into mechanically ventilated rats. After 30 min, the lungs were lavaged and the percentage of admi nistered liposomes or PC bound to AMs was determined by quantifying fl uorescence. Factors known to enhance attachment/phagocytosis by AMs in vitro were assayed to determine their effect in vivo. For example, vi tronectin (VN)-coated liposomes increased attachment from 25.2 +/- 2.3 % to 47.2 +/- 3.0% (p < 0.001), while addition of VN increased the bin ding of PC to AMs from 16.5 +/- 1.7% to 24.5 +/- 2.2% (p < 0.05). Conf ocal laser microscopy of cells obtained by lavage provided morphologic evidence of attachment/phagocytosis by AMs. This model will permit th e quantitative assessment of the interaction of fluorescently labelled liposomes or microorganisms with AMs in the lower respiratory tract o f living animals.