Activation of the aryl hydrocarbon receptor reduces the number of precursor and effector T cells, but preserves thymic CD4+CD25+Foxp3+ regulatory T cells

► Thymic Treg cells are preserved from reducing effects of AhR on precursor T cells. ► AhR activation does not increase the number of CD4+CD25+Foxp3+ Treg cells in the thymus and MLN, but increases the number of these Treg cells in the spleen. ► AhR activation decreases the number of precursor and effector T cells. ► Effects of AhR activation on T cells are partly independent of sensitization.