Anti-PC antibodies from the recombinant mouse BAB 14 were evaluated by analytical isoelectric focusing in an attempt to gain information on the crucial question of whether the recombinational event in this strain occurred in V region structural genes or in allotype-linked regulatory genes. Immune sera from BAB 14, C57BL/6 and its congenic partner CB20 (both Ighb), BALB/c and its congenic partner BC8 (both Igha) were isofocused. Antibodies bearing two distinct idiotypes, T15 Id and M511 Id, were detected by an in situ localization procedure with radiolabeled anti-T15 and anti-M511 idiotypic antibodies. The IEF spectrotypic pattern of IgG antibodies of each strain revealed separate populations of T15 Id-positive (IEF-T15) and M511 Id-positive (IEF-M511) antibodies. The IEF-T15 and IEF-M511 spectrotypes in BAB 14 most closely resembled those of C57BL/6 due to the dominant charge effect of the CH region. However, the entire set of IEF-T15 bands and a portion of the IEF-M511 bands in BAB 14 show a slight but clearly evident anodal shift in its pI relative to C57BL/6. This finding of a shift, regardless of IgG subclass, demonstrates that the difference between BAB 14 and C57BL/6 resides in the VH region and not the CH region. Thus, there is direct evidence from structural data that H chains of BAB 14 are composed of a CH segment (allotype marker) commonly expressed by C57BL/Ka (Ighb) mice and VH segment commonly expressed by BALB/c (Igha) mice. These findings are discussed in terms of recombination in structural versus regulatory genes.
This work was supported by United States Public Health Service Research Grant AI-12533 to J.L.C., by an F.G. Novy Fellowship to V.J.R., and National Institutes of Health predoctoral Traineeship 5-T32-GM07315 to J.W.