Q. Which of these is not a cell of the macrophage system?
(a) Kupffer cell 
(b) osteclasts 
(c) Langerhans cells 
(d) astrocyle

Dear student.

The correct answer is d. Astrocyte.

Kupffer cell, Langerhans cell, Osteoclast etc are part of Mononuclear phagocyte system. 

Astrocytes are star-shaped cells in central nervous system. They maintain extracellular ionic balance and forms a blood-brain barrier (BBB). 

Regards.