Bone marrow and osteoclasts
Macrophages share progenitor cells and growth factor requirements with osteoclasts, which are multinculeated giant cells that resorb bone. In this section, we see the bone marrow space at lower left, where F4/80-positive macrophages form the centre of haematopoietic islands. At the top right of this space, there is a larger, multinucleated cell osteoclast adjacent to an indentation (Howship's lacuna) in the bone matrix. This cell lacks detectable F4/80, and loss of this antigen is a useful marker for divergence of the two cell types.