In vivo identification of parasinus macrophage in the mesenteric lymph node

Macrophages beneath the marginal sinus in the lymph nodes may play a role i n defense against microorganism. The purpose of this study was to directly visualize the parasinus macrophages in the mesenteric lymph node. Fluoresce nt latex particles were injected into the appendix submucosa of rats. The m esenteric lymph node was epi-illuminated and observed with a fluorescent mi croscope. Fluorescent particles entered the marginal sinus of the mesenteri c lymph node through the afferent lymphatic vessels, and distributed diffus ely all over the marginal sinus. The particles became aggregated and inters persed 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 suspensio n was consistent with macrophages. In conclusion, we successfully visualize d parasinus macrophages in vivo, which incorporated foreign bodies and migr ated within the marginal sinus.