Comparative study of lymphatics and bllod vessels.

Abstract

Two methods were used to distinguish between lymphatic capillaries and blood capillaries at the light microscopic level: in one toluidine blue sections were embedded in epoxy resin following arterial perfusion-fixation, and in the other an immunohistochemical technique used basement membrane antisera (laminin, type IV collagen and fibronectin antisera) in indirect immunoperoxidase and immunogold-silver staining (IGSS) methods. The precise immunolocation of these basement membrane components around these capillaries was examined electron microscopically by pre-embedding immunoperoxidase and post-embedding immunogold techniques. The toluidine blue sections showed two types of capillaries: one with blue-stained lumens and the other with vacant lumens. Conventional electron microscopy revealed that capillaries with blue-stained lumens are lymphatic capillaries and capillaries with vacant lumens are blood capillaries by their fine structural characteristics. Immunohistochemical techniques using laminin or type IV collagen antiserum in both the immunoperoxidase and IGSS methods showed blood capillaries with continuous and linear reactions and lymphatic capillaries with absent or weak reactions beneath the endothelium. Immunostaining of fibronectin antiserum was observed nonspecifically around both types of capillaries and in connective tissue. Fine granular products in the IGSS method were in sharper contrast against the background and were more intensely stained and thinner than the DAB reaction products demonstrated by the immunoperoxidase method. Immunoelectron microscopy revealed greater immunoreactivity of laminin and type IV collagen antisera in the lamina densa around blood capillaries than in that around lymphatic capillaries. A striking feature was the presence of fibronectin antiserum in the intracellular organelles of blood capillary endothelium and on the surface of fibroblasts. In conclusion, toluidine blue staining following arterial perfusion-fixation is a useful technique for experimental pathologists, and the IGSS method using laminin and type IV collagen antisera is a practical light microscopic method of distinguishing between lymphatic capillaries and blood capillaries.