The heavy black pigmentation indicated by the arrow in the macrophages in this image is hemosiderin - a storage form of recycled iron. This is a bronchoalveolar lavage (BAL) sample from a patient that had pneumonia-like symptoms with two episodes of unexplained drops in hemoglobin without obvious external bleeding.
The large amount of hemosiderin is a reflection of the amount of intra-alveolar bleeding that was causing both the drop in hemoglobin and the pneumonia symptoms.
