Stimulation of human fetal lymphocytes by lipopolysaccharide B in culture. Studies on cells circulating in maternal blood.

Lipopolysaccharide B (LPS) was used in attempts to stimulate fetal cells circulating in the maternal blood during pregnancy. Crystalline leukoagglutinin (LA), the mitogenic properties of which are identical with those of phytohemagglutinin, was used as a reference mitogen. When artificial mixtures of varying proportions of lymphocytes from mothers (XX) and their newborn male infants (XY) were co-cultured in the presence of these mitogens. LPS brought about a definite enrichment of XY mitoses, indicating that even under these conditions of co-culture, LPS preferentially, though not exclusively, stimulates the infant cells. When cells from the blood of 13 women pregnant in the second trimester with a male fetus were cultured with LPS as a mitogen, all mitoses were found to be XX. Since interphase Y chromatin occurred in uncultured lymphocytes from these women (cells containing Y chromatin were found in 5 out of 6 women tested), we conclude that LPS is unable to stimulate, or at least induce mitoses, in fetal cells circulating in the blood of pregnant women. The nature of these cells is discussed.