Lack of coreceptor allows survival of chronically stimulated double-negative α/β T cells:: Implications for autoimmunity

Lymphoproliferative diseases arts characterized by massive accumulation of CD4(-)CD8(-)B220(+) (double-negative [DN]) T cells in peripheral organs. Although evidence indicates these cells are derived from mature autoreactive alpha/beta 7 cells, the significance of coreceptor downregulation is trot known. In this study, we examined the role CD4 coreceptor plays in the survival of repeatedly stimulated T cells. CD4(+/+) and CD4(-/-) 7 cells from AND T cell receptor (TCR) transgenic mice exhibited similar phenotypes after antigenic stimulation, but the CD4(-/-) T cells survived in much larger numbers than the CD4(+/+) cells upon primary and secondary major histocompatibility complex (MHC)/peptide stimulation. Enhanced survival of CD4(-/-) 7 cells was due to decreased apoptosis rather than enhanced proliferation. Similarly, circumvention of the CD4/MHC interaction by using a surrogate TCR ligand that does not engage CD4 led to significant enhancement of CD4(+/+) cells than when stimulated with MHC/peptide. Finally, we generated DN B220(+) 7 cells using an in vitro model system and showed they were more tolerant to chronic stimulation than CD4(+/+) cells. Together, these results indicate that coreceptor engagement controls expansion of normal 7 cells. In the absence of coreceptor, T cells survive chronic stimulation and express B220 as seen in autoimmune lymphoproliferative diseases.