Enhancement of murine splenic immunoglobulin secretion in vitro by supernatants from fetal and placental cell cultures

Abstract Supernatants from short-term cell cultures of fetal and placental tissues of mid-term allogeneically (CBA/Ca × C57/Bl) and syngeneically (CBA/Ca × CBA/Ca) pregnant mice were tested for B-cell enhancing activity in vitro. Immunoglobulin (Ig) secreting cells were detected by the protein-A-plaque assay and DNA synthesis was measured by the incorporation of [ 3 H]thymidine. Supernatants from placental and fetal liver cell cultures (but not fetal fibroblasts) were significantly stimulatory to spontaneous IgM (and to some extent IgG) production in a system using adult untreated spleen cells as target cells. Conditioned media were also added to LPS- and PHA-activated spleen cell cultures. In this system none of the supernatants affected the development of Ig secretors. The DNA synthesis of the target cells was slightly depressed by the addition of conditioned medium from fetal and placental cells. The results indicate that the typical increase in the number of maternal splenic Ig secretors observed in vivo during murine pregnancy could be the result of enhancing factors deriving from the placenta and the fetus (e.g. fetal liver).