A fraction of murine placental extract enhances IgA production in cultured splenocytes

Abstract During the second half of murine pregnancy there is a characteristic increase in the number of spontaneous immunoglobulin-secreting cells in the maternal spleen (IgM, IgG and IgA), the uterus-draining lymph nodes (IgG) and Peyer's patches (IgA). There are indications that signals originating from the feto-placental unit are of importance for the generation of at least some of these changes. To evaluate further the role of placental factors as regulators of maternal Ig-secretion, placental extract (PE) was separated into eight fractions by gel-chromatography and each fraction was screened for its effect on splenic (1) background DNA-synthesis, (2) background Ig-secretion and (3) Ig-secretion in lipopolysaccharide (LPS) activated B-cells (anti-Thy1.2 + complement-treated splenocytes). Similarly prepared extracts of fetuses, maternal spleen and maternal liver served as controls. All tissue extracts and splenocytes were syngeneic to avoid reaction to allogeneic determinants. Placental extract fraction did not differ significantly from the other tissue extracts in affecting background lymphocyte activity. However, fraction number 3 from placental extract (PE3, corresponding to an approximate molecular weight of 18–70 kDa) was found strongly to increase the number of IgA-secreting cells ( P ⩽ 0.001) in LPS-activated B-cells. This effect was absent or much less pronounced in the corresponding controls. Blocking of PE3-activity by antibodies against rat prolactin indicated that the enhancing activity may be attributed to proteins of the prolactin/placental lactogen/growth hormone family. This assumption was further strengthened by experiments demonstrating that prolactin exerted preferential enhancement of IgA secretion when added to LPS-activated B-cell cultures in vitro. The possible role of placental prolactin-like molecules as regulators of maternal IgA secretion is discussed.