DISTRIBUTION OF COLLOIDAL GOLD TRACER WITHIN RAT PARASTERNAL LYMPH-NODES AFTER INTRAPLEURAL INJECTION

Background: Tracer studies are an important tool to obtain information about the processes involved in the immunological response. Colloidal gold is widely used as a tracer, but its small size of label can cause some difficulty during low-resolution analysis. To overcome this difficulty, we developed a new method to follow the route of tracer movement within lymph nodes. Methods: We applied conventional X-ray analysis, X-ray fluorescence analysis (XFA) subtractional microscopy using synchrotron radiation (SR) beams, light mycroscopy, and ultrastructural analysis to study the distribution and quantity of colloidal gold coupled with albumin within rat parasternal lymph node 2, 4, 6, 8, and 10 h after intrapleural injection of the tracer. Results: At all the time points XFA-SR revealed that tracer formed a circle with a maximum concentration in the node periphery. XFA-SR measured colloidal gold concentration in the nodes reached its maximum (0.5-0.75 weight %) in 6-8 h. Substractional microscopy revealed superficially located groups of cells filled with colloidal gold tracer. Light microscopy and ultrastructural analysis confirmed that the tracer was concentrated in the reticular cells, situated in the sinuses of the node. Sinusoidal reticular cells concentrated tracer at much higher rates than sinusoidal macrophages. Four hours after injection, gold appeared in the lysosmes of the follicular reticular cells. At the same time point, evidence of antigen presentation was obtained. Antigen presentation proved to be an extremely rare event since only one ultrastructural incident was found in 150 analysed grids. Conclusion: SR is a valuable tool for the analysis of gold tracer passage within the living organism. (C) 1995 Wiley-Liss, Inc.