Htal-1 transgenic mice show a reduction in splenocytes, disorganization of the germinal center, and a defect in antigen-dependent B-cell maturation.

(A) Disorganization of germinal centers (GC) in the spleen of transgenic mice. Morphology of paraffin-embedded sections of wild-type and transgenic spleen revealed by hematoxylin eosin staining (original magnification, × 120). (B) Phenotypic analysis of B splenocytes of wild-type, low-copy (L8), high-copy (L6), and Δbhtal-1(Δb L3) transgenic mice. Cells were stained with monoclonal anti-B220–FITC and anti-CD19–PE antibodies. Percentages in quadrants refer to the lymphoid gate defined on forward and side light scatter. Analyses were performed on sex- and age-matched mice and repeated 6 times. (C) Ectopic hTAL-1 expression causes a defect in immunoglobulin isotype switch recombination. Transgenic and wild-type T-cell–depleted splenocytes were activated with 25 μg/mL lipopolysaccharide for 3 days and then stained with monoclonal anti-B220–PE-Cy5 and anti-IgG3–FITC. Percentages of IgG3-positive cells are corrected after exclusion of B220⁻ cells. (D) Electrophoretic mobility sift assay of hTAL-1 complexes in activated B-lymphocytes. Nuclear extracts (15 μg) from activated B-lymphocytes of wild-type, L6, and heterozygous L8 mice were incubated in the presence of a 5′ radioactively end-labeled oligonucleotide sequence containing the TAL-1 consensus-binding sequence. Binding competition was performed with a 100-fold excess of tal-1 cold oligonucleotide. Supershifts were obtained by using the monoclonal anti–hTAL-1 antibody BTL73. The assay illustrates that a TAL-1/E2A complex is present in transgenic-activated splenocytes and quantification of the TAL-1/E2A complex shows that its level is lower in L8 splenocytes.