An unusual lineage of alpha/beta T cells that contains autoreactive cells

In male mice that express a transgenic alpha/beta T cell receptor (TCR) specific for a male-specific peptide presented by class I Db major histocompatibility complex (MHC) molecules, we describe an unusual lineage of alpha/beta T cells that are thymus dependent but do not require selection by Db MHC molecules on thymic epithelium in the absence of the specific peptide (positive selection). These cells express the transgenic alpha/beta TCR and have the CD4-8- or CD4-8low phenotype. Cells with the latter phenotype are only detected when hemopoietic cells express both the male-specific peptide as well as Db MHC molecules. In fact, these cells are autoreactive, as they expand relatively slowly after transfer into male nude mice. Also in male but not female alpha/beta TCR transgenic mice, the CD8+ cells with the transgenic TCR bear the Pgp1 marker characteristic of mature T cells activated by antigen. CD4-8- as well as CD4-8low cells do not respond significantly when cultured with male stimulator cells but proliferate vigorously when stimulated by TCR antibodies. By this latter criterion, cells in the periphery of male alpha/beta TCR transgenic mice differ from mature male-specific T cells from female alpha/beta TCR transgenic, which become intrinsically anergic when transferred into male nude mice and cannot be stimulated significantly by TCR antibodies. Thus, intrathymic deletion does not eliminate all autoreactive T cells and it is possible that cells with an apparently "benign" autoreactivity may be involved in certain forms of autoimmunity.