CD8+ T cell depletion renders CD28-deficient mice susceptible to experimental autoimmune encephalomyelitis (EAE). In addition, CD8–/–CD28–/– double-knockout mice are susceptible to EAE. These findings suggest a role for CD8+ T cells in the resistance of CD28-deficient mice to disease. Adoptive transfer of CD8+CD28– T cells into CD8–/– mice results in significant suppression of disease, while CD8+CD28+ T cells demonstrate no similar effect on the clinical course of EAE in the same recipients. In vitro, CD8+CD28– but not CD8+CD28+ T cells suppress IFN-γ production of myelin oligodendrocyte glycoprotein–specific CD4+ T cells. This suppression requires cell-to-cell contact and is dependent on the presence of APCs. APCs cocultured with CD8+CD28– T cells become less efficient in inducing a T cell–dependent immune response. Such interaction prevents upregulation of costimulatory molecules by APCs, hence decreasing the delivery of these signals to CD4+ T cells. These are the first data establishing that regulatory CD8+CD28– T cells occur in normal mice and play a critical role in disease resistance in CD28–/– animals.
Nader Najafian, Tanuja Chitnis, Alan D. Salama, Bing Zhu, Christina Benou, Xueli Yuan, Michael R. Clarkson, Mohamed H. Sayegh, Samia J. Khoury