CONICET | Buscador de Institutos y Recursos Humanos

The term ?Mononuclear Phagocyte System? (MPS) was introduced by van Furth and Cohn in 1968 to describe a group of leukocytes that shared phenotypic features (e.g., a single nucleus) and biological functions (e.g., phagocytosis) (1). This term served originally to characterize bone marrow progenitors, blood monocytes, and tissue macrophages, under the assumption that it was a linear progression from progenitor to monocyte, and from monocyte to macrophage. Upon the discovery of dendritic cells (DC) in 1973 by the late Nobel Laureate, Ralph Steinman, and subsequent inclusion of this cell type as part of MPS in the late 1970s, the term ?MPS? undertook a specialized function for processing and presenting antigen to activate lymphocytes (2). Monocytes, DCs, and macrophages became referred to as antigen-presenting cells (APC). Today, beyond serving as primordial APCs, these cells are also known to play roles in thermogenesis, tissue development, and organ function, maintenance of homeostasis, microbiota interactions, innate immunity against pathogens, inflammation and its resolution, and wound healing and tissue repair, among others (3). Also, it is now clear that monocytes, DCs and macrophages, are not homogenous populations (4). Recent conceptual advances concerning the MPS ontogeny and development have shattered the traditional view of DCs and macrophages as linear derivates and functional variations of monocytes (5). It is predicted that the incorporation of new technologies (e.g., mass cytometry, single-cell RNA sequencing) along with the progress in imaging capacities, will continue to unveil cellular heterogeneity and behavior in different tissues, differentiation trajectories, and the identification of novel immune functions, within the mouse and human MPS (5). Therefore, as the MPS field continues its unrelenting progress, it is important to regularly revisit the MPS conceptual framework in health and disease.