Question

multiple choice question
which statement describes a macrophage.
a macrophage is a cell that lives in the bloodstream and phagocytizes antigen - antibody complexes.
a macrophage is originally a basophil that has released its histamine granules.
a macrophage is originally a monocyte that has migrated into the tissues.
a macrophage is originally a neutrophil that has been exposed to an antigen.

Explanation:

Macrophages are derived from monocytes that migrate from the bloodstream into tissues. They play a key - role in phagocytosis and immune response. The first option is incorrect as macrophages are mainly tissue - resident, not primarily in the bloodstream for phagocytizing antigen - antibody complexes. Basophils are not the precursor of macrophages, so the second option is wrong. Neutrophils are also not the origin of macrophages.

Answer:

A macrophage is originally a monocyte that has migrated into the tissues.