Little is understood of the anatomical fate of activated T lymphocytes and the consequences they have on the tissues into which they migrate. Previous work has suggested that damaged lymphocytes migrate to the liver. This study compares class I versus class II major histocompatibility complex (MHC)–restricted ovalbumin-specific T cell antigen receptor (TCR) transgenic mice to demonstrate that after in vivo activation with antigen the emergence of CD4−CD8−B220+ T cells occurs more frequently from a CD8+ precursor than from CD4+ T cells. Furthermore, this change in phenotype is conferred only by the high affinity native peptide antigen and not by lower affinity peptide variants. After activation of CD8+ cells with only the high affinity peptide, there is also a dramatically increased number of liver lymphocytes with accompanying extensive hepatocyte damage and elevation of serum aspartate transaminase. This was not observed in mice bearing a class II MHC–restricted TCR. The findings show that CD4−CD8−B220+ T cells preferentially derive from a CD8+ precursor after a high intensity TCR signal. After activation, T cells can migrate to the liver and induce hepatocyte damage, and thereby serve as a model of autoimmune hepatitis.

No abstract

The origin of TCR-αβ+ CD4−CD8− cells is unclear, yet accumulating evidence suggests that they do not represent merely a default pathway of unselected thymocytes. Rather, they arise by active selection as evidenced by their absence in mice lacking expression of class I MHC. TCR-αβ+ CD4−CD8− cells also preferentially accumulate in mice lacking expression of Fas/APO-1/CD95 (lpr) or Fas-ligand (gld), suggesting that this subset might represent a subpopulation destined for apoptosis in normal mice. Findings from mice bearing a self-reactive TCR transgene support this view. In the current study we observe that in normal mice, TCR-αβ+ CD4−CD8− thymocytes contain a high proportion of cells undergoing apoptosis. The apoptotic subpopulation is further identified by its expression of B220 and IL2Rβ and the absence of surface CD2. The CD4−CD8− B220+ phenotype is also enriched in T cells that recognize endogenous retroviral superantigens, and can be induced in TCR transgenic mice using peptide/MHC complexes that bear high affinity, but not low affinity, for TCR. A model is presented whereby the TCR-αβ+ CD2− CD4−CD8− B220+ phenotype arises from high intensity TCR signals. This model is broadly applicable to developing thymocytes as well as mature peripheral T cells and may represent the phenotype of self-reactive T cells that are increased in certain autoimmune conditions.