Morphological changes in paracortical high endothelial venules to single and repeated application of oxazolone to mouse skin.

Morphological changes in paracortical high endothelial venules (HEV) have been studied after single and repeated applications of oxazolone to mouse skin. The primary response was characterized by a rapid and marked vascular dilatation, by marked increase in the cross sectional area of the vessel wall and in the size of the individual endothelial cells, as well as increased accumulation of lymphocytes in HEV walls. These changes regressed (in the more long lasting response). The transitory structural alterations may be related to increase of blood flow, increased flow of cells from the thymus to the stimulated lymph nodes as well as increased transport capacity of endothelial cells based on augmentation of their surface area. These features are closely related to other cellular events such as a prominent blastoid reaction in the paracortex as well as an associated cellular depletion of the thymus.