Studies on the surface phenotype and functions of dendritic cells in parenchymal lung tissue of the rat

Immunohistochemical analysis of frozen sections of rat lung tissue identified a widely distributed population of highly pleiomorphic Ia+ cells in alveolar septal walls, which are negative for the pan-macrophage marker ED4 and the related markers ED1, ED2 and ED9. Semi-purified dendritic cells (DC) prepared from lungs of rats exposed to an aerosol of ovalbumin (OA) triggered modest levels of proliferation of OA-immune T cells in vitro, demonstrating the potential of these cells in surveillance for inhaled antigens in vivo. Lung wall also exhibited modest stimulatory activity in mixed lymphocyte/leucocyte reaction (MLR) assays. Overnight incubation of the DC in T-cell culture supernatant markedly increased their T-cell stimulatory properties, concomitant with increased expression of Ia. These results suggest that analogous to epidermal Langerhans' cells, lung wall DC can effectively bind inhaled antigens in situ, but require additional maturation/activation signals before they can efficiently present the antigen to T cells.