The yield for IgM was quite similar between the different lines
(Fig. 3A); often up to 500 μg/ml as identified in wt controls and only occasionally somewhat reduced but never less than IGF-1R inhibitor half of the wt level analyzed in parallel. Thus, despite some variation, the IgM concentrations in all lines were in good agreement with the levels produced in wt rats kept under the same conditions. Near normal increase in IgM titer was also seen after immunization and in all lines specific IgM levels were similar to wt (not shown). For IgG purification on protein A, the results were split as low and normal levels were identified (Fig. 3B). For HC14, HC17 and wt this revealed 500–1000 μg IgG/ml serum; this level was established from several experiments and agrees with previous findings despite the suboptimal purification of rat IgG using protein A (Bruggemann et al., 1989 and Osborn et Alpelisib al., 2013). A consistently lower amount, ~ 10% of normal levels was identified in HC10 and HC13 animals, where some rats had barely more than 50 μg IgG/ml serum. In these rats specific IgG was lacking
after immunization while HC14 and HC17 produced extensive immune responses frequently similar to wt rats (Fig. 3C). Immunizations were carried out using 4 different antigens, β-galactosidase (β-gal), human progranulin (hPG), ovalbumin (OVA) and hen egg lysozyme (HEL), all of which failed to work efficiently in HC10 and HC13. Previously we showed that a chimeric IgH locus with human VHs, Ds and JH segments linked to rat C-region genes and control sequences, produced highly diverse and near-normal expression levels of antibodies with human idiotypes (Osborn et al., 2013). Here we assess the performance of 4 translocus rat-lines, with silenced endogenous IgH locus (Menoret et al., 2010), carrying the same human VH-region but different rat CH-regions. The comparison was aimed at identifying minimal CH transloci, which would permit near normal expression. In these lines, the IgM expression level with a diverse repertoire of human VH-D-JH
rearrangement was very similar, with surface μ+ B-cells and secreted IgM in serum comparable to wt rats. This suggests that DNA rearrangements with developmental stages from pro to pre to immature B-cells are adequately performed as described (Almqvist and Martensson, Rebamipide 2012). In previous transgenic IgH lines carrying only human CH-genes reduced levels of serum IgM and IgM+ B-cells have been identified (Green and Jakobovits, 1998, Nicholson et al., 1999 and Brüggemann et al., 2007), even with Eμ, Cμ and downstream regions analogous to our transgenic constructs (Lonberg et al., 1994, Mendez et al., 1997 and Nicholson et al., 1999). The suboptimal performance of fully human IgH constructs is likely to reflect imperfect interaction of the human C-genes with the rodent cellular signaling machinery.