Lymphatic and blood microvasculature organisation in pulmonary sarcoid granulomas

Pulmonary sarcoid granulomas are characterised by their elective distribution along collecting lymphatics. However, relationships between granulomas and intralobular lymphatics or blood microvascularisation have not been investigated. Therefore, we undertook a specific analysis of blood capillaries and lymphatics supplying sarcoid granulomas to identify additional clues to understanding the pathophysiogenesis of these lesions. Six pulmonary samples were immunolabelled with D2-40, anti-CD34 and anti-CD31 antibodies, paying particular attention to the relationships between lymphatics and granulomas, and the pattern of blood microvessels supplying sarcoid lesions. A morphometric study of granulomas included their distance to lymphatics and a three-dimensional reconstruction of a granuloma in its lymphatic context. Intralobular granulomas were closely associated with lymphatics; apart from a few granulomas, blood capillaries stopped at the outer border of the fibrous ring surrounding granulomas, and perigranuloma capillaries were particularly scarce. Our observations of the lymphatic and blood microvascular environment of intralobular pulmonary sarcoid granulomas provide evidence for the critical role of lymphatics in the emergence of these lesions. Moreover, pulmonary sarcoid lesions could be considered avascular structures, thereby providing new insights into the understanding of the granuloma physiology and the distribution of blood-borne therapeutic agents.