Spectrotypic analysis of passively acquired and newly synthesised IgG antibodies in the neonatal and young mouse.

Isoelectric focussing with autoradiography has been used to analyse the selective nature of passive transmission of specific anti-Ig allotypic antibodies from the mother to the young mouse, and to study the generation of spectrotypic (clonal) diversity of autologous IgG2a (carrying the paternal inherited Igh-1b allotype) in BALB/c X SJL/J F1 (Igh- 1ab heterozygote) mice. Transmission of anti-allotypic antibody to neonatal mice was found to be pI restricted, with selection favouring electrophoretically fast IgG. Comparison of the antibody spectrotype in maternal serum, milk and neonatal serum revealed that the pI restriction in transmission operates at the level of the neonatal gut. Analysis of the paternally inherited Igh-1b IgG2a molecules as they are first synthesised and secreted into the neonatal serum revealed an extensive polyclonality on first detection by the very sensitive focussing assay. It can be deduced that IgV region diversity is generated by IgG2a-synthesising cells prior to, or at the time of, the first secretion of this class of antibody into the serum.