Dilatation of high endothelial venules in compartments of rat lymph nodes with abundant cortical mast cells.

Previous work has shown that the method of killing animals and of fixation of lymph nodes determines the appearance of high endothelial venules. Routine procedures produce a narrowing of the high endothelial venules whilst in situ fixation of lymph nodes results in their dilatation. More recently, routine procedures have demonstrated that lymph nodes from athymic and some euthymic ageing rats have occasional compartments in which the high endothelial venules are dilated in association with an increased population of cortical mast cells. These observations suggest that mast cell products may influence the physiological state of the high endothelial venules and affect the recruitment of blood lymphocytes.