| Abstract: | We previously reported that the pulmonary intravascular macrophages (PIMs) of sheep, goat, and calf lung contained a heparin and a lipolytic lipase sensitive surface coat by using tannic acid as a component of paraformaldehyde-glutaraldehyde-based fixative. The implication of this sensitivity was that the surface coat was predominantly comprised of lipoprotein-like substance. In this study we report that monastral blue (MB) used as a vascular tracer interacted with the coat globules and lost its original particulate appearance. Its precise localization in the PIMs was in combination with altered macromolecules of the surface coat in the form of lipid droplets, which conformed to the conventional view of neutral lipids. In contrast, pigment particles examined in their native state resembled metalic particles as electron-dense eliptical rods. The lipid droplets were subsequently internalized through endocytic route and found their access into the lysosomal compartments of PIMs at the electron microscopic level. Lamellar bodies (LLBs) arose from the lysosomal matrix after the entry of lipid droplets in the secondary lysosomes. Acid phosphatase activity was located in secondary lysosomes as well as in endosomes. These observations suggest that coat granules of the PIMs acted as a carrier of exogenous MB particles to deliver the complex to the lysosomal compartment where partial digestion lead to the formation of lamellar bodies. The implications of MB (cationic dye) as a vascular tracer for studying phagocytic index of PIMs in the light of their coat and the rapid development of LLBs are discussed. It is proposed that MB by initially combining with the surface coat provokes mobilization of intracellular lipid pools. In this way metabolism of vasoactive lipid in the PIMs is stimulated to influence the dynamics of pulmonary circulation in the calves.© Willey-Liss, Inc. |
