Ontogenetic Change in the Antigenic Specificity of the Chick Spleen

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Abstract
The mean wt. of the spleens of 17-day-old embryonic chicks bearing chorio-allantoic grafts of spleen from adult chickens is over 100% greater than the mean wt. of spleens of controls bearing grafts of heart or gonad. The effect is class-specific, for grafts of spleen from adult mice evoke no enlargement, but is only partially organ-specific. The substances responsible cannot be detected in 9-day-old embryonic chick spleen, but increase progressively during later embryonic and post-hatching stages. Evidence presented from histological and serological analyses of spleens and sera of host embryos favors a tentative interpretation that substances released from the grafts act as intermediate templates and catalyze the synthesis of substances with configurations identical to those in the graft, resulting in the enlargement of the homologous organ of the host. Results of 1200 precipitin tests indicate that saline extracts of 9-, 12-, and 18-day-old embryonic chick spleen contain, in addition to an antigenic fraction held in common with extracts of 18-day-old and adult brain, a spleen-specific fraction, identical, or closely related, to a combining group found in extracts of adult spleen. Moreover, as shown by reciprocal absorption methods, an additional antigenic substance is present in extracts of 18-day-old and adult spleen, which is not present in 9- and 12-day embryonic spleen. These data suggest a correlation between the progressive increase with age in the ability of spleen grafts to evoke enlargement of host''s spleen, and the differentiation, during a similar period in ontogeny, of a specific antigenic group.