The degree of polyclonality of the naive CD4⁺ T-cell repertoire in E17 HLA-DRB1*1501 mice is similar to the degree of polyclonality in E17 mice expressing a murine MHC class II complex. Genomic DNA was isolated from splenic CD4⁺ T cells obtained from naive conventional E17 mice (E17 murine MHC class II) and naive E17 HLA-DRB1*1501 mice (E17 human MHC class II) and analyzed for the combinational diversity of V-J gene rearrangements of the T-cell receptor-β chain using multiplex PCR. (A) Box plots demonstrating the diversity of V-J gene rearrangements of the T-cell receptor-β chain (TRB) in naive conventional E17 mice (E17 murine MHC class II) and naive E17 HLA-DRB1*1501 mice (E17 human MHC class II) in percent (CD4⁺ mTRB diversity). Ten animals, 5 male (5m) and 5 female (5f), from each mouse strain were included in the analysis. ns indicates not significant. (B) Three-dimensional representation of the repertoire of the CD4⁺ T-cell receptor-β chain for one representative naive conventional E17 mouse (E17 murine MHC class II) and one representative naive E17 HLA-DRB1*1501 mouse (E17 human MHC- class II). Each peak represents the rearrangement of a family of V genes, relative to the rearrangement of the J genes. The intensity of these rearrangements is represented on the z-axis.