Assessment of nonspecific Cre activity in Bach2^fl/flFoxp3^YFP-Cre mice. (A) Nonspecific deletion of the Bach2^fl allele in Tconv cells from Bach2^fl/flFoxp3^YFP-Cre mice. PCR-based detection of the indicated alleles from Foxp3⁻ Tconv cells and Foxp3⁺ Treg cells isolated by FACS from Bach2^fl/flFoxp3^YFP-Cre mice. Amplified fragments of control Tlr9 (left), unexcised Bach2^fl (middle), or excised Bach2^ex alleles (right) are shown and indicated with black triangles. The Bach2^ex allele results from Cre-mediated excision of the Bach2^fl allele. The presence of detectable Bach2^ex amplicons from both Tconv and Treg cells indicates nonspecific Cre-mediated excision of the Bach2^fl allele in Tconv cells, which is incomplete, as reflected by the presence of a residual Bach2^fl amplicon from Tconv cells. (B) Specific induction of RFP fluorescence within a fraction of CD4⁺ T cells upon tamoxifen treatment. Representative flow cytometry plot showing RFP intensity among CD4 T cells from spleens of Bach2^fl/flFoxp3^{EGFP-Cre-ERT2}Rosa26^flSTOP-tdRFP mice treated without (–TAM) or with (+TAM) tamoxifen in the diet for 8 wk. Data are representative of two repeated experiments with four mice per group. Numbers in gates show percentages. Bars and error show mean and SEM.