TRANSFER OF IGA FROM ALBUMIN INTO THE YOLK-SAC DURING EMBRYONIC-DEVELOPMENT IN THE CHICKEN

In the chicken, maternal antibodies are transferred into the egg and s ubsequently transported into the developing embryo. IgG is the primary immunoglobulin isotype of the egg yolk, while IgM and IgA are mainly found in the albumen. However, considerable amounts of IgM and IgA of unknown origin are found one day prior to hatching in the yolk sac. Th ese antibodies are not synthesized de novo by the embryo proper, thus pointing to a transfer from the albumen into the egg yolk during devel opment. To further address this question, I-125 labelled chicken IgA w as injected into the albumen of freshly laid eggs. On day 21 of embryo nic development, I-125-IgA was found in the yolk sac content. On avera ge (n = 6) 36.2 +/- 7.2 % of the injected radioactivity was recovered from this compartment and shown to be associated with IgA. Comparison of total IgA in the albumen of freshly laid eggs with the amounts of I gA in yolk sac content showed similar results with a 44 % transfer rat e. An increase of the IgA concentration in the yolk sac was first dete ctable between days 14 and 16 of embryonic development. These data cle arly show that IgA is transferred from the albumen into the yolk sac, most likely by a transport across the yolk sac membrane.