Macrophages are big, motile cells with a single nucleus that are part of the cellular immune system. As part of the mononuclear-phagocyte-system (MPS) they perform many tasks in denfense against germs.
Therir most important task are the phagocytosis of microorganisms and other foreign particles as part of the unspecific immune response and antigen-presentation.
Their cytoplasm contains a high number of lysosomes (see picture), that contain lytic enzymes that kill phagocytized germs.
On their surface macrophages form cell-protusions, so calles pseudopodia.