These drawings, showing phagocytic white blood cells (leukocytes) from various species, are those of Elie Metchnikoff, an early pioneer in the field of immunity who shared the Nobel Prize in 1908 with Paul Ehrlich, another founding father of modern immunology. Metchnikoff was the first to recognize the ability of leukocytes to move toward pathogens (chemotaxis) and subsequently surround and kill them (ideas that were highly controversial at the time). Because of their roles as both sentinels and effectors of the innate and adaptive immune system, leukocytes are frequently measured and monitored in clinical practice. An increased white blood cell count (leukocytosis) is one of the most common signs of infectious and inflammatory diseases.
Neoplasms of immune cells, which include the leukemias, the lymphomas, and the plasma cell tumors, are less common than benign disturbances involving leukocytes but also more clinically important. Beginning in the latter half of the 20th century, white blood cell neoplasms have been on the leading edge of advances in oncology. Ease of sampling of leukemic cells in the blood of affected patients was one of the factors that attracted early investigators and led to the development of curative chemotherapy regimens for childhood acute lymphoblastic leukemia, and Hodgkin lymphoma was the first human cancer to be cured with radiation and combination chemotherapy. The field now finds itself at the forefront of a genomic revolution that is laying the groundwork for increasingly precise molecular diagnoses and more effective, less toxic targeted cancer therapies.
Drawings of phagocytes from several species are shown. In each panel, the phagocytes have consumed different microorganisms, which are seen within the cytoplasm of the phagocytes. (Reproduced with permission from Metchnikoff E. L’immunite dans les Maladies Infectieuses. Masson & Cie, Paris, 1901.)