In vitro and in vivo production of interleukin-6 by fetal mononuclear cells.

We examined the functional activity of cord mononuclear cells (MNCs) to produce interleukin (IL)-6 in vitro and in vivo. We stimulated fetal T-cell, B-cell, and macrophage fractions with mitogens. The supernatant of each stimulated cord cell fraction contained a comparable amount of IL-6 to that of each adult cell fraction activated similarly, suggesting functional maturity of cord MNCs' ability to produce IL-6. We then examined fetal cells' activities to produce IL-6 in response to perinatal infections, especially to intraamniotic infections (IAI). Among the cord MNCs from fetuses with IAI, macrophages were major cells producing IL-6. The serum IL-6 level in the fetuses with IAI was elevated, but it decreased to normal levels after antibiotic treatment; this finding indicates that IL-6-mediated host defense mechanisms by cord MNCs are triggered by perinatal infections.