Haemopoietic islands in bone marrow

This is a section of the bone marrow of an animal carrying an infection with bacillus-Calmette-Geurin. The F4/80 staining highlights large stellate macrophages that form the centre of haemopoietic islands. Additionally, small round F4/80-positive cells (monocytes) can be seen migrating away from the haemopoietic islands, and in the walls of the vessels (the open spaces) about to enter the circulation.