Leucocyte endothelial interactions

The accumulation of leucocytes in damaged tissues depends upon the interaction of leucocytes with the endothelium in the damaged tissue, see figure 2. There is a continuum between the stages of rolling, adherence and transmigration.

Most of the manifestations of inflammation in a tissue, (leucocyte accumulation, filtration of fluid and protein) only occur in the post capillary venule.

Figure 7: Schematic representation of the molecular mechanism of rolling in leucocytes in post capillary venules. a) shows the unactivated state with no expression of selectins on the leucocyte of the endothelium. b) shows the activated state with P-selectin expressed on the endothelium, P-selectin is released from the Weibel-Palade body in endothelial cells. Expression is induced by hypoxia, free radicals, histamine and thrombin. In c) the leucocyte has grabbed on to the endothelium with binding of sialyated Lewis to P-Selectin. The binding is not very tight as the leucocyte may pop off again with the appearance of rolling on microscopy.