Relationship between lymphocyte emigration and vascular endothelium in chronic inflammation

Small blood vessels within areas of chronic inflammation which contain large numbers of lymphocytes develop unusually thick walls. Combined histological and electron microscope study shows that the thickening is due to hypertrophy of endothelial cells which come to resemble the endothelium of post-capillary venules in lymphoid tissue. Vessels of this type have been found in experimental granulomas induced by injection of Freund's adjuvant or killed tubercle bacilli and in human biopsy material from cases of rheumatoid arthritis and Hashimoto's disease of the thyroid. Comparison with the developing Peyer's patch in young rats shows that the unusual vessels in granulomas are very similar in endothelial cell size, pattern of distribution, extent of lymphocyte migration and degree of carbon leakage to post-capillary venules of the immature Peyer's patch. Study of the time at which lymphocytes appear in large numbers within the granuloma or developing Peyer's patch and the time at which thickened vessels are first seen suggest tha the endothelial changes are a consequence and not a cause of lymphocyte emigration. The stimulus to endothelial hyperthrophy appears to be massive sustained migration of lymphocytes, but the functional significance of this change in vascular structure is not clear.