In order to study the development and differentiation of the immunological activity of human fetus, Ig G, A and M cells are demonstrated in the thymus and the spleen by means of Avidin Biotin Peroxidase Complex method.
The results show (1) The Ig G cells appear in the thymus about 4 months of gastation and Ig A and M cells about 6 months of gestation in the thymus and the spleen in our human fetal specimens. (2) The Ig G cells are seen more often than Ig A and M cells both in the thymus and in the spleen. (3) Ig G, A and M cells are observed mainly in the medulla of the thymus and in the red pulp of the spleen mostly around the capillary vessels.