What are the two classes of macrophages?

The two classes of macrophages are:

- Fixed macrophages - These are macrophages that are located in specific tissues and organs and do not circulate in the bloodstream. Examples include Kupffer cells in the liver, alveolar macrophages in the lungs, and microglia in the brain.

- Free macrophages - Also known as circulating macrophages, these are macrophages that circulate in the bloodstream and can migrate to sites of infection or inflammation. They include monocytes and tissue macrophages.