Endothelial cells appear to play a dual role in the pathogenesis of bronchial asthma. These cells participate in recruitment of leukocytes to the site of the allergic response by releasing neutrophil chemotactic factors and modulating leukocyte-adhesion molecules. Enhanced expression of adhesion molecules has been detected in endothelial cell cultures subjected to various types of stimuli, including such cytokines as tumor necrosis factor alpha and interleukin-1 beta. In addition, there is evidence to suggest that antibodies directed against an endothelial cell component may also contribute to the inflammatory processes associated with severe asthma.