Localization of rabbit gamma globulins in the mouse visceral yolk sac placenta. 
The yolk sac placenta has been implicated previously in transmission of passive immunity to the fetus.  This work uses an immunohistochemical technique devised by Sternberger et al. (' 69) to study this problem.  Rabbit serum containing gamma globulins was injected into the uterine lumen of the White Swiss mouse during the last third of pregnancy.  Two or four hours later yolk sacs were removed and fixed in 2% paraformaldehyde or freeze-dried and fixed with paraformaldehyde vapors.  Finely chopped tissue was treated with (1) sheep antiserum to rabbit serum gamma globulin, (2) an antigen-antibody complex consisting of horseradish peroxidase and rabbit anti-horseradish peroxidase and (3) hydrogen peroxide and 3,3'-diaminobenzidine.  Reaction product was heavily concentrated in visceral yolk sac endodermal cells, frequently deposited in endothelial cells of vitelline vessels, and rarely in the serosal basement membrane and mesothelial cells which border the exocoelomic cavity.  This supports evidence of other workers that the yolk sac membrane rapidly absorbs substances with which it comes in contact, transport into vitelline vasculature is a route of transfer from mother to fetus, and possible transfer into the exocoelomic cavity and thence to the amniotic cavity may occur in mice.