In vivo biological effect of allogeneic cultured thymic epithelium on thymus-dependent immunity in athymic nude rats.

We have extended our previous study of induction of T-lymphocyte immunocompetence in athymic nude rats by cultured epithelium (CTE) of syngeneic origin to that by CTE of allogeneic origin. Immune responsiveness (IgG-class antibody and delayed-type hypersensitivity) after ovalbumin immunization is detectable by 4-6 weeks after transplantation. However, the antibody appears at a slower rate when compared with heterozygous immunocompetent littermates. Seven weeks after transplantation phytohaemagglutinin responsiveness of spleen cells is detectable, and in T-dependent areas of lymphoid organs lymphocytes with helper and non-helper T-cell phenotype are present, but at lower levels than those in heterozygous immunocompetent littermates. Levels comparable to that of immunocompetent rats are reached about 20 weeks after transplantation. Since CTE contains thymocytes, control experiments consisted of transplantation with high numbers of allogeneic freshly isolated thymocytes in athymic nude rats. These animals showed IgG-class antibody formation after ovalbumin immunization, but at lower levels than CTE-treated rats, and were almost negative in T-cell immunocompetence assessed in the other assays. We conclude that CTE of allogeneic origin induces T-cell immunocompetence in athymic nude rats to the level of heterozygous immunocompetent littermates. This study adds to the rationale of CTE transplantation applied in treatment of thymic dysfunction.