mononuclear phagocyte system vs system of macrophages

mononuclear phagocyte system and system of macrophages both are nouns.

Word	Noun	Adjective	Verb	Adverb
mononuclear phagocyte system	Yes	No	No	No
system of macrophages	Yes	No	No	No

As nouns, mononuclear phagocyte system and system of macrophages are synonyms defined as:

mononuclear phagocyte system and system of macrophages: a widely distributed system of free and fixed macrophages derived from bone marrow

Other synonyms of mononuclear phagocyte system include MPS.

mononuclear phagocyte system (noun)	system of macrophages (noun)
a widely distributed system of free and fixed macrophages derived from bone marrow	a widely distributed system of free and fixed macrophages derived from bone marrow