AN ANALYSIS OF THE INITIAL REACTION IN THE SEQUENCE RESULTING IN HOMOLOGOUS SPLENOMEGALY IN THE CHICK EMBRYO

¹ Department of Embryology, Carnegie Institution of Washington, Baltimore 10, Maryland, and Wabash College, Crawfordsville, Indiana

1. As demonstrated by their capacity to induce splenomegaly and by tritiumthymidine labeling, some of the cells of chorioallantoic grafts of adult chicken spleen colonized the chorioallantois, spleen, and other organs of the host embryo within two days.

2. The capacity of the embryonic environment not only to support immune reactions but also to permit maturation of mechanisms of immune response was demonstrated by the serial propagation of embryonic spleen cells in non-inbred embryos. A cumulative response was obtained, beginning with the fifth or sixth transfer, approximately paralleling the normal development in the chicken of the ability to elicit splenomegaly.

3. However, stimulation of the host spleen was not obtained by the serial propagation of embryonic spleen cells in inbred embryos nor in a series in which the single initial donor was derived from a different inbred line. This suggested that the accumulation of a threshold number of reactive cells is necessary for the stimulation.

4. Induction of mutual interbreed "tolerance," as indicated by reduced effectiveness of adult chicken spleen to induce splenomegaly, was not obtained by previous chorioallantoic grafts of embryonic spleen.

5. The pre-immunization of adult chickens of one inbred line by skin homografts from a second line did not render the former's spleen capable of an enhanced reaction but, instead, reduced its effectiveness to elicit host spleen enlargement. It was suggested that such hyperimmunized cells undergo allergic death.

6. Attention is redirected to the proliferation of cells of the host following an initial graft-versus-host reaction. It is again suggested that this granulocytic response is a tissue-specific growth reaction resulting from the liberation of cell products in necrotic foci created in the initial immune reaction.