Distribution of Immunoglobulins During Embryogenesis in the Chicken*

Whereas the yolk of freshly-laid eggs contains only IgG, apart from traces of IgA, we were able to measure, on average, 0.145 mg/ml IgM and 0.207 mg/ml IgA in the yolk sac contents of 21-day-old chicken embryos. Up to the 14th embryonic day, IgG is exclusively contained in the yolk sac contents. It was not possible to demonstrate an increase in the amount of immunoglobulins present by comparing the amounts of IgM and IgA in freshly-laid eggs and in the yolk sac contents of 21-day-old embryos. The offspring of hens with experimentally-induced agammaglobulinemia did not begin with the production of the immunoglobulin isotypes IgG, IgM and IgA until after hatching. From these results the conclusion can be drawn that the immunoglobulins IgM and IgA are transferred from the egg white to the yolk sac contents during the last third of embryonic development. Embryonic synthesis of these immunoglobulins can be discounted as a result of this study. Synthesis was found to be initiated between the 2nd and 7th day of life for IgG, between the 2nd and 4th day of life for IgM and between the 6th and 13th day of life for IgA.