This generated 4 transgenic lines with several founders each, which all showed productive integration of 3 BACs carrying the same VH region but different C-genes. In Fig. 1 the gray bar illustrates how tandem integration of the same human VH6-1, all D and JH segments but with different rat C-regions might have been achieved. For HC10 only Hu BAC3 was included in conjunction with the C-region Tofacitinib cost but in a separate experiment, generating HC15, both human VH BACs, Hu BAC6-3

and Hu BAC3, were integrated together with Hu-Rat Emma. As we found no expression differences between these lines, except in the number of used VH genes we have grouped the results together. Correct integration was identified by PCR and confirmed by human VHDJH rearrangements to rat Cs. For the analysis several founders of each line were bred to homozygosity with IgH knock-out rats in which the endogenous JH segments had been deleted (Menoret et al., 2010). The 4 transgenic lines

were compared LBH589 after breeding into the JHKO/JHKO background. Flow cytometry assessed if the introduced chimeric IgH loci could reconstitute normal B-cell development and RT-PCR analysis, using PBLs, determined if diverse human (VHDJH)s were produced (Fig. 2). Staining cell suspensions of bone marrow, spleen and PBLs for IgM and CD45R (B220) (Fig. 2A) revealed in HC10 and HC13 a slight reduction in the numbers of IgM+CD45R+ cells, while in HC14 and HC17 the numbers were very similar to wt controls. However, as we do see differences in cell populations between individual rats, from both transgenic and wt controls, this may suggest that all 4 lines, HC10, HC13, HC14, HC17, show near normal

B-cell development Erlotinib in vitro with adequate numbers of immature and mature B-cells. This is supported by the finding of highly diverse human VHDJH rearrangement of Cμ H-chain, when analyzing 50–100 random sequences for each line (Fig. 2B). Similar to wt controls these IgM sequences showed little hypermutation. Extensive diversity of rearranged VHDJH transcripts was also found for Cγ sequences but only in HC14 and HC17, with few class-switch products obtained in HC10 and HC13. Many of the chimeric class-switch products were extensively mutated, but normal levels of IgG transcripts were only found in HC14 and HC17 while HC10 and HC13 produced little. As shown previously, B-cell development in HC14 is very similar to wt rats with mutational changes predominantly found in VHDJH-Cγ transcripts (Osborn et al., 2013). As comparable results were obtained for HC17 we can conclude that both these lines allow B-cell development, while in HC10 and HC13 B-cell maturation stages following IgM expression appear to be suboptimal. The level of serum Ig from ~ 3 month old rats kept in isolators was compared in ELISA (not shown) and after purification on SDS-PAGE (Fig. 3A and B).