Mechanism of immune suppression by murine neonatal fluids.

Pretreatment of peritoneal exudate cells (PEC) for 24 to 48 hr with mouse amniotic fluid (MAF) results in a marked reduction in their ability to present antigen in a macrophage-T cell dependent antigen-induced lymphocyte proliferative assay. Since we showed that MAF did not inhibit the uptake of antigen by the antigen-presenting cells, presumably the site of action is either on "processing," T-macrophage interactions and/or on the secretion of soluble factors by macrophages. Whether suppression is the result of a direct effect on MAF on the antigen-presenting cell or indirectly via another cell type present in the PEC preparations was not established by this study. However, our data suggest that a major (although perhaps not sole) site of action of the suppressive factor(s) in MAF is at the level of the antigen-presenting cell. The biologic relevance of these in vitro observations is discussed in regard to the defects of immune function in fetal and neonatal animals.