T-Lymphocyte Subsets in the Embryonic Spleen Undergoing a Graft-Versus-Host Reaction

Allogeneic immunocompetent T cells injected into chicken embryos induce a graft-versus- host reaction (GVHR) whose most prominent manifestation is splenic hyperplasia. The highly inbred CC and CB strains of chickens used here are, respectively, homozygous for the B4 or B12 MHC haplotypes. By means of a panel of immunological reagents, including alloantisera and monoclonal antibodies against public domains of the T-cell receptor, CD4, CD8, and the inducible interleukin-2-receptor light chain (CD25), it is shown that the bulk of cells in the enlarged spleen are of host origin and do not express markers typical of mature T or B lymphocytes. Among recipient splenocytes, the quantitatively most important population consists of TCRαβ^-TCRγδ CD4^-CD8⁺CD25⁺ (TCRO) lymphocytes. Donor cells encountered in the spleen prevalently exhibit a TCRαβ⁺CD4⁺CD8^-CD25⁺ phenotype and proliferate in vivo. The data demonstrate that nonspecific host and potentially specific donor- derived cellular elements contribute to splenomegaly.