Characterization of Eμ-FOXP1 transgenic mice. (A) Illustration of the hFOXP1 transgene construct used for the generation of transgenic mice (left). Southern blot analysis on several transgenic lines to estimate transgene copy number (right). (B) Human and mouse FOXP1 messenger RNA levels were measured by qRT-PCR in spleen, bone marrow, and liver from unimmunized WT and Eμ-FOXP1 mice (n = 3 per mouse line and genotype) and presented relative to endogenous murine FOXP1 (2^−ΔΔCt). Significance was determined by 2-tailed unpaired Student t tests. (C) Human FOXP1 expression by qRT-PCR in B CD19⁺, T CD3⁺, and granulocyte Gr1⁺ from unimmunized mice and GC B220⁺Fas⁺GL7^hi and non-GC B220⁺Fas⁻GL7⁻ cells isolated from SRBC-immunized WT and Eμ-FOXP1 mice (n = 3 per mouse line and genotype). Data are presented relative to GAPDH (2^−ΔCt). (D) Representative IHC sections from WT and Eμ-FOXP1 mice (line L1) showing the distribution and expression of FOXP1 (brown, sum of human and murine levels) in splenic lymphoid follicles. (E) Representative fluorescence-activated cell sorter (FACS) profiling of the hematopoietic compartments in the thymus and bone marrow of 2-month-old unimmunized WT (n = 3) and Eμ-FOXP1 (n = 3) mice.