Selection of antitoxins by the foetal membranes of rabbits

Abstract

Antibodies pass from the uterine lumen of pregnant rabbits into the foetal body fluids. It has been shown that antibodies formed in rabbits enter the foetal circulation by this route much more readily than those formed in horses or cows. It is the intention of this paper to investigate further this selective admission to the foetal circulation, to determine if there is a differential selection of heterologous antibodies according to the species in which they were produced and if this selectivity changes with foetal age. Antitoxins were employed throughout and were prepared in rabbit, man, guinea-pig, dog, horse and cow, against diphtheria or tetanus toxin or Clostridium welchii α-toxin. Mixtures of sera from two or three of these species, each serum containing a different antitoxin, were administered so far as possible. The antitoxin concentrations observed in the experimental samples were corrected to unit concentration in the serum administered, the term concentration quotient (c.Q.) being used for this quantity. Measured in this way the entry of antitoxin to the foetal serum varied with the species in which the antitoxin was produced; rabbit, man, guinea-pig, dog, horse and cow forming a descending series in that order. The entry of antitoxin into the amniotic fluid, or the foetal stomach contents derived from it, does not vary with the species in which the antitoxin was produced. This is so also for the maternal serum. Thus the species in which an antitoxin is produced affects the concentration at which it will appear in the foetal serum but not that at which it will appear in the other foetal body fluids or in the maternal serum. The entry of antitoxin prepared in rabbits to the foetal circulation increases with foetal age from 20 to 26 days after copulation and decreases thereafter.