The mononuclear phagocyte system: role in expression of immunocompetence in neonatal and adult life.

The cells of the mononuclear phagocyte system are critical elements in host defense. They are essential to many specific immune processes in addition to their well-recognized role in nonspecific resistance. In this report we describe studies of the influence of the maturation of this system of cells on the capacity of the neonatal rat to generate specific immune responses. In addition, studies of human cord blood monocyte function are presented along with data demonstrating a previously unrecognized synergistic action between monocytes and a heat labile, nonantibody, serum factor which may play an important role in host defense. Finally, data are presented demonstrating that one of the recognition processes used by monocytes for cellular interaction is dependent upon a system of natural lectin-like receptors on the monocyte cell surface which recognize membrane-bound oligosaccharides on other cells.