Studies on haemolymph nodes. IV. Comparison of the route of entry of carbon particles into parathymic nodes after intravenous and intraperitoneal injection.

Haemolymph nodes are found in certain mammals including man. In the rat they are located near the kidneys, spleen and thymus. A distinctive feature is that their sinuses contain numerous erythrocytes. For renal and splenic haemolymph nodes, the erythrocytes appear to be extrinsic in origin, entering the node via its afferent lymphatics (Hogg et al. 1982; Abbas et al. 1983). In the present study we investigated the drainage of carbon particles injected intraperitoneally or intravenously into the parathymic haemolymph nodes. Carbon particles injected intraperitoneally reached the nodes rapidly, within minutes and in large quantities, via the afferent lymphatics draining principally from the diaphragmatic peritoneum. Carbon particles injected intravenously entered the nodes much more slowly, reaching a maximum after 5-7 d, and in much smaller amounts, although the pattern of distribution was similar, spreading from the subcapsular sinus into the intermediate and medullary sinuses. No carbon particles were found crossing the walls of high endothelial venules. Carbon particles injected intravenously reach the parathymic nodes from peripheral lymph via the afferent lymphatics. Whilst accepting that there are significant biological differences between carbon particles and erythrocytes it seem possible that erythrocytes, like injected carbon particles, may enter the nodes by a similar route.