Helios defines T cells being driven to tolerance in the periphery and thymus.

The expression of the Ikaros transcription factor family member, Helios, has been shown to be associated with T-cell tolerance in both the thymus and the periphery. To better understand the importance of Helios in tolerance pathways, we have examined the expression of Helios in TCR-transgenic T cells specific for the gastric H(+) /K(+) ATPase, the autoantigen target in autoimmune gastritis. Analysis of H(+) /K(+) ATPase-specific T cells in mice with different patterns of H(+) /K(+) ATPase expression revealed that, in addition to the expression of Helios in CD4(+) Foxp3(+) regulatory T (Treg) cells, Helios is expressed by a large proportion of CD4(+) Foxp3(-) T cells in both the thymus and the paragastric lymph node (PgLN), which drains the stomach. In the thymus, Helios was expressed by H(+) /K(+) ATPase-specific thymocytes that were undergoing negative selection. In the periphery, Helios was expressed in H(+) /K(+) ATPase-specific CD4(+) T cells following H(+) /K(+) ATPase presentation and was more highly expressed when T-cell activation occurred in the absence of inflammation. Analysis of purified H(+) /K(+) ATPase-specific CD4(+) Foxp3(-) Helios(+) T cells demonstrated that they were functionally anergic. These results demonstrate that Helios is expressed by thymic and peripheral T cells that are being driven to tolerance in response to a genuine autoantigen.