Transmission electron micrograph of a neutrophil after ingestion of bacteria. Bacteria are seen in the cytoplasm of the white cell. Neutrophil (also known as neutrophils or occasionally neutrocytes) are the most abundant type of granulocytes and the most abundant type of white blood cells in most mammals. They form an essential part of the innate immune system. They are formed from stem cells in the bone marrow. They are short-lived and highly motile, or mobile, as they can enter parts of tissue where other cells/molecules wouldn't be able to enter otherwise. Magnification @ 26,000x, 8x10 print.