ULTRASTRUCTURAL-LOCALIZATION OF CD44 IN THE RAT LUNG IN EXPERIMENTAL GOODPASTURES-SYNDROME

Although CD44 is known to be involved in a wide array of cell to cell and cell to matrix interactions, its role in immune-mediated disease i s not well understood. Therefore, using immunogold electron microscopy we have determined the precise !localisation of CD44 in the rat lung in experimental Goodpasture's (GP) syndrome, a model of immune-mediate d pulmonary disease. In normal rat lung CD44 was present on the surfac e of alveolar macrophages but was not detectable on endothelium. In GP syndrome there was strong CD44 expression on all infiltrating inflamm atory leucocytes, both adherent to endothelium and within the alveolar spaces and interstitium. However the most striking finding was the pr ogressively strong antibody staining for CD44 on pulmonary endothelium of alveolar capillaries and larger vessels over the 21 days of GP syn drome. In situ hybridisation confirmed that the endothelial CD44 stain ing was due to local protein synthesis. All epithelial cell surfaces, including bronchial epithelium and type I and II alveolar epithelial c ells, were negative in normal rat lung and GP syndrome. De novo CD44 e xpression by endothelial cells during the progression of GP syndrome m ay contribute to leucocyte recruitment and cell-mediated lung injury.