The architecture of rat lymph nodes. IV. Distribution of ferritin and colloidal carbon in the draining lymph nodes after foot-pad injection.

Rat popliteal and the iliac lymph nodes were examined after foot-pad injections of colloidal carbon and ferritin-tetramethylrhodamine isothiocyanate. Carbon rapidly entered medullary sinuses, but the entry of carbon into the interstitium was prohibited by avid phagocytosis, by sinus macrophages and by the lymphoendothelium, which apparently formed a barrier to diffusion. In contrast, little carbon was phagocytosed in subcapsular sinuses, from where the particles entered the underlying cortex through holes in the lymphoendothelium created by penetrating frilly cells. The distribution of ferritin was similar to that of carbon. Both carbon and ferritin localized poorly in follicles; however, preinjection of specific antibody caused enhanced follicular localization of ferritin. By electron microscopy clusters of ferritin molecules were found on the surface of dendritic cells. These cells showed different morphology from that of the interdigitating cells of the paracortex. The latter cells did not bind ferritin to their surface, even in the presence of specific antibody.