Coloured scanning electron micrograph (SEM) of neutrophils phagocytosing (engulfing) Aspergillus fungus. Neutrophils are the most abundant white blood cell and are part of the body's immune system. Several Aspergillus species can cause diseases in humans, including allergic disorder, respiratory infection and invasive disease. Some species produce the toxin aflatoxin, which is also carcinogenic. Two red blood cells are also seen.