This comprehensive treatise on the reticuloendothelial system is a project jointly shared by individual members of the Reticuloendothelial (RE) Society and bio medical scientists in general who are interested in the intricate system of cells and molecular moieties derived from those cells which constitute the RES. It may now be more fashionable in some quarters to consider these cells as part of what is called the mononuclear phagocytic system or the lymphoreticular system. Nevertheless, because of historical developments and current interest in the subject by investigators from many diverse areas, it seems advantageous to present in one comprehensive treatise current information and knowledge con cerning basic aspects of the RES, such as morphology, biochemistry, phylogeny and ontogeny, physiology, and pharmacology as weIl as clinical areas including immunopathology, cancer, infectious diseases, allergy, and hypersensitivity. It is anticipated that by presenting information concerning these apparently heterogeneous topics under the unifying umbrella of the RES attention will be focused on the similarities as weIl as interactions among the cell types constitut ing the RES from the viewpoint of various disciplines. The treatise editors and their editorial board, consisting predominantly of the editors of individual vol umes, are extremely grateful for the enthusiastic cooperation and enormous task undertaken by members of the biomedical community in general and especially by members of the American as weIl as European and Japanese Reticuloendothe lial Societies."

An extraordinary development of the knowledge, concepts and biomedical applications has occurred during the past two decades in the biological sciences, including the Reticuloendothelial Sys- tem (RES). For example, it is now widely recognized that distinct classes of cells are involved in the recognition of "exogenous" invaders of the body such as microorganisms and other foreign an- tigens, as well as of "endogenous" parasites represented by trans- formed neoplastic cells and altered "self" antigens. Prominent among cell populations involved in such recognition of antigens and subsequent immune responses are those constituting the RES. In recent years, there has been much discussion and indeed contro- versy as to what constitutes such a system and even whether the term "RES" is appropriate. Some investigators feel that the phago- cytes are the most important cells of the RES as they playa major role in the defense mechanism of the host. Mononuclear phagocytes include tissue macrophages ~s well as circulating monocytes and their precursors. Although phagocytosis is a major functional ac- tivity, it is only one of their several functions. The important role of phagocytes and other mononuclear cells in antibody forma- tion, cell-mediated immunity, specific and non-specific resistance to microorganisms and tumor cells, as well as homeostatic adjust- ments in general has become the focus of attention for many inves- tigators.