- Phagocytoses bacteria, cellular debris, and senescent RBCs.- Long life in tissues.- Name differs in each tissue type (eg, Kupffer cells in liver, histiocytes in connective tissue, Langerhans cells in skin, osteoclasts in bone, microglial cells in brain).

- Differentiate from circulating blood monocytes.- Activated by γ-interferon (from Th1 cells).

- Can function as antigen-presenting cell via MHC II.

- Important component of granuloma formation (TB, sarcoidosis).

- Lipid A from bacterial LPS binds CD14 on macrophages to initiate septic shock.