reticuloendothelial system
Summary
The reticuloendothelial system, now more properly called the mononuclear phagocyte system, is the network of tissue macrophages derived from monocytes that filter blood and lymph and phagocytose pathogens, debris, and senescent cells. It includes Kupffer cells, splenic macrophages, alveolar macrophages, microglia, and osteoclasts.
Detail
These cells share the functions of phagocytosis, antigen presentation on MHC class II, and cytokine secretion. Their distribution explains a great deal of pathology. Splenic macrophages remove encapsulated bacteria opsonized by antibody and complement, which is why asplenic and functionally asplenic patients, including those with sickle cell disease, are at risk of overwhelming sepsis from Streptococcus pneumoniae, Haemophilus influenzae type b, and Neisseria meningitidis and require vaccination. The spleen also removes Howell-Jolly bodies, whose presence on blood film signals hyposplenism. Kupffer cells clear portal blood, which is why the liver is exposed to gut-derived organisms and why iron overload deposits there. The system is where intracellular pathogens establish themselves — Leishmania, Histoplasma, Salmonella Typhi, Brucella, Mycobacterium — and where lipid accumulates in storage disorders, giving Gaucher cells with crumpled-tissue-paper cytoplasm and the foamy macrophages of Niemann-Pick disease.
Sources
- Janeway's Immunobiology
- Robbins Basic Pathology
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