Differences within mono- and dizygotic twin-pairs in spectrotypes and clones of IgG2 antibodies to pneumococcal polysaccharide type 1 and C-polysaccharide after vaccination.

Spectrotypes and clones of antibodies against pneumococcal capsular polysaccharide (Ps) type 1 and C-polysaccharide (C-Ps) were determined before and after immunization with a polyvalent pneumococcal Ps vaccine in 84 mono- or dizygotic twins. The method used was a micromodification of a rapid isoelectric focusing-affinity (IEF-affinity) immunoblot technique in agarose permitting characterization of isotype, light chain and Gm type. After vaccination the anti-type 1 Ps + anti-C-Ps clones were different in 75% of the monozygotic and 79% of the dizygotic twins. The anti-type 1 Ps clones differed among 72% of the monozygotic and 85% of the dizygotic twins (P > 0.05). Each twin had from zero to three clones producing IgG2 antibodies against type 1 Ps. A total of six different clones could be distinguished among all the twins. Vaccination enhanced the already actively secreting B-cell clones in 56 twins and newly recruited clones in 11 of the 84 twins; six among the 48 mono- and five among the 36 dizygotic twins. These new clones differed among the twins. Spectrotypes varied between all twins within the pairs. The fact that all twins differed in spectrotype is due to post-translational microheterogenity of the antibodies, events which are thus not genetically determined. The observation that even monozygotic twins possessed and responded with different clones within the pairs indicates that the V-region genes, which determine the final specificity of B cells, either differ from the original germ-line V region genes, e.g. owing to hypermutations or junctional diversity, or the rearranged germ-line genes occur accidentally although highly restricted.