Identification of lymph and blood capillaries by immunohistochemical staining for various basement membrane components.

In the present report we analyzed the presence and distribution of various basement membrane (BM) proteins in normal blood and lymph vessels with special emphasis on BM-associated heparan sulfate proteoglycan (HSPG) when compared to the BM-components collagen IV, laminin and fibronectin. We found that normal lymph capillaries have a BM that contains only collagen IV and small amounts of laminin, but almost no BM-associated HSPG and fibronectin, while blood capillaries showed a BM comprising of all components tested for. Larger lymphatics, however, were indistinguishable from blood vessels on the basis of BM staining. Lymphangiomas showed a BM pattern similar to that of lymph capillaries. Our findings provide evidence that the differential staining of BM-components may represent a reliable method for morphological distinction between blood and lymph capillaries. A comparison of these results with the BM-pattern in other functionally specialized blood vessels (glomerulus, sinusoids) provides evidence that the BM-composition may have some major impact on the functional properties. Thus, it is conceivable that the lack of HSPG in lymph capillaries may be essential for a free influx of fluid and proteins into these capillaries, which may have been extravasated into the interstitium.