This white blood cell acts as the body's trash collector.  Monocytes eat and digest dead cells, debris, germ parts, and even whole germs.  They acts as an antigen-presenting cell, eating germs and informing other immune cells what the pathogens look like.

Description:  Called a monocyte while in the bloodstream, macrophage when it reaches the tissues.   Macrophage literally means "big eater."  It is the largest white blood cell.

Location:  Patrols the bloodstream until it "smells" the enemy, chemical messages from other immune cells, or the stench of dead cells.  Once it catches a scent, it quickly moves through the tissues to the site of infection or cell damage.

Weapons:  Its appetite.  The macrophage can eat anything smaller than itself.  If the pathogen is too large to eat, dozens of macrophages can join together to form giant cells in an attempt to engulf the enemy.

Appearance:  16-20 micrometers in height, contain a single large nucleus.  Many macrophages can join together to form giant cells.

Source: arise from stem cells in the bone marrow.

Life span:  Months to years.

Number: Around 1-4 billion in an average adult's bloodstream with many more living in the body's tissues.