DENDRITIC CELLS AND THEIR PRECURSORS ISOLATED FROM HUMAN BRONCHOALVEOLAR LAVAGE - IMMUNOCYTOLOGIC AND FUNCTIONAL-PROPERTIES

Human bronchoalveolar lavage (BAL) has been described to contain, besides a large number of alveolar macrophages (AM) (similar to 95%), small numbers of monocyte-like cells (similar to 2%) and dendritic cells (DC) (similar to 0.4%). To separate AM (high autofluorescence) from DC, we used a fluorescence activated cell sorter (FACS) to separate BAL cells into a low autofluorescent (LAF) fraction and a high autofluorescent (HAF) fraction. Immunocytologic and functional properties of these fractions were investigated. The LAF fraction was composed of acid phosphatase (APh)- and RFD9-negative cells, which were strongly positive for HLA-DR, L25, RFD1, and CD68. A portion of these cells expressed CD1a (22%) and My4 (60%). The marker pattern of these cells is reminiscent to that of intraepithelial bronchial DC and to that of blood DC, The majority of the LAF cells had a monocyte-like morphology, but after overnight culture the percentage of LAF cells with long cytoplasmic extensions (DC morphology) was strongly augmented (from 18 to 51%). The HAF fraction contained 100% AM, strongly positive for APh, HLA-DR, CD68, RFD7, and RFD9. In culture, the LAF cells formed clusters with T cells and vigorously stimulated the proliferation of allogeneic T cells and naive (CD45RO-negative) T cells. BAL and LAF cells produced higher responses in nonsmokers than in smokers. In contrast, HAF cells did not form clusters with T cells and did not stimulate allogeneic T cell proliferation. HAF cells even suppressed mitogen-driven T cell proliferation. We conclude that human BAL cells can be separated with a FACS into (1) high autofluorescent AM with T cell-suppressive properties and (2) low autofluorescent accessory cells with a very strong T cell-stimulatory potential. These accessory cells show many features of dendritic cells, but do have some monocyte characteristics as well.