**3.7 Splenic macrophages**

Currently, four different types of macrophages have been known to colonize the spleen: marginal zone macrophages, marginal metalophilic macrophages, tangible body macrophages and red pulp macrophages [25]. All except red pulp macrophages are derived from circulating blood monocytes. Red pulp macrophages differentiated from yolk sac and fetal liver progenitors that took residence in the spleen during embryogenesis. Red pulp macrophages act immune sentinels and in healthy conditions they primarily phagocytose platelets and red blood cells for iron metabolism [25]. Tangible body macrophages on the other hand phagocytose B cells that have undergone apoptosis. Marginal zone and marginal metallophillic macrophages function to blood-borne pathogens and clear them from circulation.
