CD163 and glioblastoma: Fig. 4E illustrates strongly labeled CD163 expressing brain macrophages within brain tissue around a blood vessel and the cellular density “gradient” displayed by them may be a reflection of their recent origin from bone marrow which can be demonstrated experimentally in animal studies. Strong and largely diffuse immunoreactivity for CD163 was typically present in necrotic tumor areas where most of the staining was found extracellularly (Fig. 4F). It should be mentioned that occasional ramified microglial cells can also exhibit CD163 expression in glioblastoma and other diseases (Fig. 4H).