Secretion of tumor necrosis factor during fetal and neonatal development of the mouse: ontogenic inflammation

Inflammation plays an important role in homeostasis of the body. We therefore can assume that an inflammatory state occurs during ontogenesis of animals. To address this problem, we examined the ability of tumor necrosis factor (TNF), one of the inflammatory mediators, to be secreted by mouse cells during development. We cultured cells prepared from various parts of fetuses (10-19 days of gestation) and postnatal brains by collagenase digestion and assayed the secreted TNF activity by the L-929 cytotoxicity test. We found TNF activity by fetal cells without any stimulation. The spontaneous secretion of TNF was relatively high at around 13-15 days of gestation. The secretion was enhanced by lipopolysaccharide (LPS), showing that fetal cells are in an activated state for TNF secretion. These TNF activities were neutralized completely by rabbit anti-murine TNF antibody. Spontaneous and LPS-enhanced secretion by postnatal brain cells reached a peak around 7 days after birth, and thereafter declined rapidly. This time course was well correlated to the increase in the weight of brain. The producing cells were negative in macrophage marker surface antigen, and heterogeneous in relation to adherence and phagocytic activity, showing that TNF is secreted by various types of cells in the fetal body. These results suggest the presence of an inflammation-like state during ontogenesis. We consider that this "ontogenic inflammation" may be the prototype of inflammation, which can regulate homeostasis of the adult body.