Light micrograph of macrophages (the many circular cells with blue nuclei, filling the field of the picture) containing hemosiderin pigment (the small brown dots). The macrophages take in the hemosiderin pigment as a function of their natural role of ingesting possibly toxic substances as part of the innate immune response. The hemosiderin pigment comes from the breakdown of blood in tissues such as occurs after injury and bleeding. Haematoxylin and eosin stained tissue section. Magnification: 400x when printed at 10cm.