DNA synthesis and production of interleukin 1 by lymph node macrophages in culture

When bovine lymph node cells are cultured for several days the adherent macrophage population increases by as much as tenfold. This increase in cell number is primarily due to cell division, which reaches a maximum on day 4 or 5 of culture. Although the presence of the nonadherent cells seems required for cell division, we have been unable to detect a macrophage growth factor in either the nonadherent cell populations. The adherent cells were identified as macrophages based on positive esterase staining, the presence of Fc receptors, β-glucuronidase activity, and phagocytosis. Moreover, these adherent cells produced interleukin 1 (IL 1) after exposure to lipopolysaccharide in serum-free medium. Approximately 10⁷ macrophages were stimulated to produce about 900 units of IL 1 in a 24-hr period. Thus, the bovine lymph node preparation is a potential source of a large number of macrophages capable of dividing in culture and of producing IL 1.