Ultrastructural localisation of CD44 in the rat lung in experimental Goodpasture's 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 is 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-mediated pulmonary disease. In normal rat lung CD44 was present on the surface of alveolar macrophages but was not detectable on endothelium. In GP syndrome there was strong CD44 expression on all infiltrating inflammatory leucocytes, both adherent to endothelium and within the alveolar spaces and interstitium. However the most striking finding was the progressively strong antibody staining for CD44 on pulmonary endothelium of alveolar capillaries and larger vessels over the 21 days of GP syndrome. In situ hybridisation confirmed that the endothelial CD44 staining was due to local protein synthesis. All epithelial cell surfaces, including bronchial epithelium and type I and II alveolar epithelial cells, were negative in normal rat lung and GP syndrome. De novo CD44 expression by endothelial cells during the progression of GP syndrome may contribute to leucocyte recruitment and cell-mediated lung injury.