In vivo identification of parasinus macrophages in the mesenteric lymph node

Macrophages beneath the marginal sinus in the lymph nodes may play a role in defense against microorganism. The purpose of this study was to directly visualize the parasinus macrophages in the mesenteric lymph node. Fluorescent latex particles were injected into the appendix submucosa of rats. The mesenteric lymph node was epi-illuminated and observed with a fluorescent microscope. Fluorescent particles entered the marginal sinus of the mesenteric lymph node through the afferent lymphatic vessels, and distributed diffusely all over the marginal sinus. The particles became aggregated and interspersed 3 hr after injection, suggesting that particles were incorporated by phagocytes. The number of these particle-laden phagocytes increased up to 12 hr after injection, and then declined. Some phagocytes migrated rapidly within the marginal sinus. Morphology of these phagocytes in cell suspension was consistent with macrophages. In conclusion, we successfully visualized parasinus macrophages in vivo, which incorporated foreign bodies and migrated within the marginal sinus.