Abstract 2064 Pulmonary Development Platform, Saturday, 5/1

The development of the vasculature in the lung requires signals for the proliferation, migration, and adhesion (retention) of endothelial cells to the branching bronchioles and alveolar septae. We previously reported the generation of a monoclonal antibody (mAb), 5B6-E4, which can inhibit endothelial cells from localizing to ureteric bud branches in embryonic kidneys grown in vitro (AJP 272:F79-85, 1997; AJP 727:F153-159, 1997). The antigen recognized by the 5B6-E4 mAb was purified, using sequential anion exchange, heparin sepharose and hydrophobic interaction chromatography, and identified as laminin receptor protein (LRP). We investigated the role of LRP in endothelial cell targeting during lung development. Purified LRP mediated attachment of endothelial cells (and other cell lines) to substratum in an in vitro assay. In addition, dual indirect immunofluorescence revealed that LRP was expressed in the mesenchyme and colocalized with endothelial cells in developing embryonic day 14-18 rat lungs. Functional significance for this association was noted when embryonic day 14 left lobe rat lungs were grown in vitro for five days. An extensive arborization of endothelial cells in a honeycomb pattern surrounding the bronchial branches was detected and quantitated by immunofluorescence. There was a 48% reduction in the number of endothelial cell networks surrounding epithelial branches in the presence of the 5B6-E4 mAb (50 µg/ml) compared to an isotype matched control (168 ± 30 versus 323 ± 38, respectively, p = 0.0034). The branching epithelial network was not affected. These studies establish a new critical function for LRP in endothelial cell targeting during lung development.