Introduction According to the intentions of the organizing committee of the IVth European Workshop of Inflammation this contribution is meant to give an overview of the present-state-of-the-arts concerning the structural reaction pattern of endothelial cells to various injurious stimuli. In order to achieve this goal within the allotted space at least in part, we have confined this article to the endothelial cells which line the microvasculature. This selection is based on the facts that (1) it is the microvessels which govern the supply of substrates to the tissues and (2) that it is the terminal vascular bed which plays a pivotal role during inflammatory reactions which are the main concern this meeting is centered around. Since the majority of the structural alterations described herein can ultimately be attributed to changes of the cell membrane, possibly its fluidity, the plasmalemma appears to represent the main target for most of the noxious stimuli. The cell membrane, however, does not only reside at the various surfaces of the cell (luminal, abluminal, and intercellular), but it also occurs in the form of vesicles which are cell membrane derivatives (Fig. l a). These endothelial or micropinocytic vesicles can be found either attached to the inner and outer surface membranes or lying free within the cytoplasm (Figs la, 3b). Endothelial reaction patterns related to their morphology and not to the various injurious agents [1-3] may therefore be classified in the following order: (1) reactions of the luminal and abluminal cell membranes, (2) reactions of the plasmalemmata along the lateral cell borders, (3) reactions of the vesicular membranes and (4) disturbances of cell membrane permeability characteristics.
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