Identification of macrophages and dendritic cells in the osteopetrotic (op/op) mouse

We used a panel of monoclonal antibodies and immunocytochemistry to identify macrophages and dendritic cells in mice that are deficient in macrophage colony stimulating factor (M-CSF or CSF-1) because of the recessive osteopetrotic (op/op) mutation. Prior work had shown that osteopetrosis is associated with a lack of osteoclasts, phagocytic cells required for remodelling in bone. Additional macrophage populations proved to be very M-CSF dependent. op/op mice had few and sometimes no peritoneal cavity phagocytes, splenic marginal zone metallophils, and lymph node subcapsular sinus macrophages. Other populations, however, reached substantial levels in the absence of M-CSF, including phagocytes in the thymic cortex, splenic red pulp, lymph node medulla, intestinal lamina propria, liver (Kupffer cells), lung (alveolar macrophages) and brain (microglia). Dendritic cells, which are specialized accessory cells for T-dependent immune responses and tolerance, were readily identified in skin and in the T-dependent regions of spleen, lymph node and Peyer's patch. The identification of dendritic cells utilized antibodies to MHC class II products and four different antigens that are primarily expressed by these accessory cells. Our findings indicate that only a few macrophage populations are critically dependent upon M-CSF in vivo. With respect to dendritic cells, the data are consistent with prior in vitro work where it was noted that GM-CSF but not M-CSF supported dendritic cell viability, function and growth.