Innate immune functions of macrophage subpopulations in the spleen.

In the different compartments of the spleen, macrophage populations can be found that have different functions depending on their localization. In the lymphoid compartment of the spleen, the white pulp, macrophages are in essence similar to populations found in lymph nodes and other organized secondary lymphoid organs. In the red pulp, large populations of classical scavenger macrophages are found that, in addition to scavenging blood-borne debris, are involved in iron recycling by phagocytosis of effete red blood cells. The most conspicuous macrophage populations of the spleen are located in the marginal zone. Strategically positioned in the bloodstream and adorned with unique sets of pattern recognition receptors, they play an important role in host defense by bridging the innate and adaptive immune systems. In this review, the various macrophage subsets of the spleen are described.