Passage of Bacteriophage φ X 174 Across the Placenta in Guinea Pigs. ∗

Abstract

Discussion and summary

These studies indicate that a virus particle, bacteriophage φX 174, incapable of infecting mammalian cells, can cross the placenta and gain access to the foetal circulation. The possibility of in vitro contamination of foetal blood samples during cardiac puncture of the foetus can be excluded since: a) the washing procedure of the foetus was shown to be effective after deliberate contamination of the foetus's skin; b) after injection of phage into pregnant guinea pigs, separate bleedings of 0.5 ml and 0.1 ml from the foetal heart usually showed a 5-fold difference in amount of φX in the 2 samples; this difference was not observed in deliberately contaminated foetuses from pregnant guinea pigs not injected with φX. It is unlikely that endotoxin contamination of phage preparations was responsible for the transplacental passage of virus because of virtual absence of biologically detectable endotoxin in the preparations of phage employed and the failure of an injection of endotoxin with phage to increase the amount of phage found in the foetal circulation. There was no apparent difference in phage transfer between foetuses of markedly different weights, 56–120 g.

The route of transplacental passage of phage is as yet uncertain. The failure to find a gradient in concentration from amniotic fluid to foetal blood (the latter sometimes had a higher phage concentration) suggests that phage is not transferred by this route. Previous studies of placental transfer of large proteins indicate that the splanchnopleure is the principal transfer organ in guinea pigs(7).

The question arises as to whether the placenta is an effective barrier in preventing intrauterine viral infections. The following findings are relevant to this question: a) in the guinea pig, the difference between maternal and foetal blood virus concentrations was approximately 105⁵–10⁶ and transfer usually was not demonstrated when maternal φX concentration was below 10⁷/ml; b) the φX particle is an unusually small virus (approximately 250 angstroms in diameter).