Lymphatic endothelium-specific hyaluronan receptor LYVE-1 is expressed by stabilin-1(+), F4/80(+), CD11b(+) macrophages in malignant tumours and wound healing tissue in vivo and in bone marrow cultures in vitro: implications for the assessment of lymphangiogenesis

Lymphangiogenesis is a novel prognostic parameter for several cancers that is preferentiallyquantified by immunohistochemistry of the lymphatic endothelium-specific hyaluronanreceptor LYVE-1. Recently, the specificity of LYVE-1 was challenged by serendipitousobservations of LYVE-1 expression in rare tissue macrophages. As expression of thehyaluronan receptor-like molecule stabilin-1 is shared by sinusoidal endothelium andmacrophages, a thorough analysis of LYVE-1 expression was performed using macrophagespecificmarkers in vivo and in vitro. In murine tumour models and excisional woundhealing, LYVE-1 expression occurred in a subset of CD11b+, F4/80+ tissue macrophagesthat preferentially co-expressed stabilin-1. Upon comparison of single- and double-labellingimmunofluorescence, it became apparent that LYVE-1+ macrophages mimic sproutingand collapsed lymphatic vessels. In vitro, LYVE-1 expression was induced in 25–40% ofmurine bone marrow-derived macrophages upon exposure to B16F1 melanoma-conditionedmedium and IL-4/dexamethasone. By FACS analysis, 11.5% of bone marrow-derivedmacrophages were LYVE-1+, stabilin-1+ double-positive, while 9.9% were LYVE-1+,stabilin-1− and 33.5% were LYVE-1−, stabilin-1+. Northern and western analyses confirmedexpression of LYVE-1 mRNA and protein in bone marrow-derived macrophages. In thelight of the current debate about true endothelial trans-differentiation versus endothelialmimicry of monocytes/macrophages, LYVE-1+, stabilin-1+ non-continuous endothelial-likemacrophages will require further developmental and functional analyses. In conclusion,the findings imply that LYVE-1 staining must be supplemented by double labelling withmacrophage markers in order to differentiate clearly between LYVE-1+ lymphatics andLYVE-1+ tumour-infiltrating macrophages. This improved approach will help to clarify theprognostic significance of lymphangiogenesis in malignant tumours.Copyright  2006 Pathological Society of Great Britain and Ireland. Published by JohnWiley & Sons, Ltd.