Recent development of the mononuclear phagocyte system: in memory of Metchnikoff and Ehrlich on the 100th Anniversary of the 1908 Nobel Prize in Physiology or Medicine

Monocytes/macrophages are critical for both immunity and homoeostasis. They are the outposts of the immune system in detecting invading pathogens or foreign antigens for homoeostatic clearance and antigen processing for the initiation and effector stages of both innate and adaptive immunity. In addition, monocytes/macrophages often function as control switches for immune system balance between pro- and anti-inflammatory reactions. In the beginning of this article, I would like to briefly introduce the achievements of Metchnikoff and Ehrlich in immunology, including Metchnikoff's cell theory, since they have both greatly influenced the advancement of modern immunology. Additionally, I will honour the 100th anniversary of the 1908 Nobel Prize in Physiology or Medicine. Next, I would like to emphasize the concept of the MPS (mononuclear phagocyte system) by examining recent developments regarding the MPS. Thus the article consists of three parts. The first part describes the regulation of growth and differentiation in the MPS. The second part addresses how the key macrophage transcription factor gene PU.1 and the csf1r (colony-stimulating factor-1 receptor gene) play a critical role in haematopoietic myelopoiesis, or the generation of the cells of the MPS. The third part describes PMA-induced monocyte/macrophage differentiation and immune modulation of suppressor macrophages. Finally, this review discusses the latest findings and implications regarding the MPS and macrophages.