Dissociation of the RES and immune components in the transient splenic response of embryos and neonatal chicks to immunization.

Immunization with mouse erythrocytes (MRBC) elicited transient splenic enlargement as well as PFC formation in immunocompetent 7, 10, and 14 day chicks. An early enlargement within two days was followed by a decline and a second enlargement by day six. Only the early enlargement was observed when MRBC or Percoll was administered to neonatal chicks and late embryos. No significant splenomegaly was observed following cell transfer of bone marrow, spleen, leucocyte, thymocyte or bursal cell suspensions from B haplotype-compatible donors. During the adoptive immune response in embryo hosts, a minor early peak was observed that was followed by an elevated or progressive increase in spleen size. The data suggest that the early splenic response reflects primarily RES-vascular activity and the later enlargement is the consequence of immune proliferation.