An immunohistochemical study on phenotypic heterogeneity of human pulmonary vascular endothelial cells

The existence of a subpopulation of human vascular endothelial cells (EC) has been demonstrated in the liver with the aid of immunohistochemical techniques. In this study, we investigated the antigenic and functional properties of the vascular EC in human lung. Alveolar capillary EC shared antigens with a peripheral blood monocyte/macrophage subset capable of presenting soluble antigens and triggering autologous mixed lymphocyte reactions. That is to say that the alveolar capillary EC were HLA-DR+, OKM1-, and OKM5+. In addition, these EC frequently expressed interleukin-1. These facts suggest that alveolar capillary EC may play an important role in immunological responses in the lung. The antigens were, however, absent or only faintly visible on the vascular EC of medium and small vessels. In contrast, Factor VIII/von Willebrand factor antigen (FVIIIRAg), which is produced in vascular EC was heavily stained in the EC of medium and small vessels, but only weakly stained in the alveolar capillary EC. These immunohistochemical findings suggest that in different anatomical compartments in the lung vascular EC express phenotypic properties heterogeneously. They may play differing biological roles or serve different immunological functions in normal and pathological states in the lung.