Quantitative and spectrotypic analysis of paternal IgG2a expression in normal and allotype-suppressed mice.

The synthesis and clonal diversity of IgG2a molecules bearing the paternally inherited immunoglobulin allotype have been examined in the offspring of matings between BALB/c mothers (Igh-1a) and SJL or C57BL/10 males (both Igh-1b) using a sensitive quantitative single radial immunodiffusion in gel assay and isoelectric focusing with autoradiography. In normal litters, the first detectable paternally-marked IgG2a is extensively polyclonal in both F1 crosses (i.e. diversity precedes expression); however, there is a delay of 2-3 weeks in the first appearance of the clonally diverse set of molecules when these are coded by the SJL genome, compared with the C57BL/10. Delayed maturation of allelically-excluded Igh-1b-expressing B cells in the (BALB/c X SJL)F1 may explain the unique susceptibility of these offspring to chronic allotype suppression when exposed to maternal anti-Igh-1b antibodies in early life. We find that, although such suppressed mice may begin life with a (delayed) synthesis of polyclonal IgG2a of paternal allele (Igh-1b), the condition of chronic suppression later imposed in the majority of mice is associated with spectrotype (clonal) simplicity.