Splenic macrophage subsets and their function during blood-borne infections

The spleen is one of the major immunological sites for maintaining blood homeostasis. Previous studies showed that heterogeneous splenic macrophage populations contribute in complimentary ways to control blood-borne infections and induce effective immune responses. Marginal metallophilic macrophages (MMM Phi s) and marginal zone macrophages (MZM Phi s) are cells with great ability to internalize blood-borne pathogens such as virus or bacteria. Their localization adjacent to T- and B-cell-rich splenic areas favors the rapid contact between these macrophages and cells from adaptive immunity. Indeed, MMM Phi s and MZM Phi s are considered important bridges between innate and adaptive immunity. Although red pulp macrophages (RpM Phi s) are mainly considered scavengers for senescent erythrocytes, several data indicate a role for RpM Phi s in control of infections such as blood-stage malaria as well as in the induction of innate and adaptive immunity. Here, we review current data on how different macrophage subsets recognize and help eliminate blood-borne pathogens, and, in turn, how the inflammatory microenvironment in different phases of infection (acute, chronic, and after pathogen clearance) influences macrophage function and survival.