Macrophages are specialized cells involved in the detection, phagocytosis and destruction of bacteria and other harmful organisms as well as senescent cells and detritus. They are key regulators in both innate and adaptive immunity, however, they are also known for their role in tissue homeostasis, development and malignancy. They originate from blood monocytes and differentiate in different tissues.

Bone marrow (BM) macrophages are involved in hematopoietic stem cell (HSC) homeostasis and erythropoiesis. Osteal macrophages support HSC survival and retention in the BM and central macrophages are surrounded by erythroblasts to support erythropoiesis. Pyrenocyte phagocytosis during enucleation is also carried out by BM macrophages. Moreover, there are pathological situations in which BM macrophages are aberrantly activated. Hemophagocytic lymphohistiocytosis (HLH) is a syndrome of pathologic immune activation characterized by clinical signs and symptoms of extreme inflammation. It can be a familial disorder or a sporadic condition in association with different triggers. Bone marrow hemophagocytosis is one of its diagnostic criteria among with others such as fever, splenomegaly,  cytopenia, hypertriglyceridemia, and elevated ferritin.