Previously (9), I found that immunization of rabbits with antibody directed against variable region heavy chain VH polypeptides of a1 allotype induced the production of antiidiotype (anti-Id) molecules that appeared to bear images of the original a1 allotype. I now show that these anti-Id molecules can be fractionated into two populations: one population (a2a3- anti-Id) that lacks the nominal VH a2 or a3 allotype of the rabbit from which it was derived, and another population (a2a3+ anti-Id) that expresses these allotypes. Both anti-Id populations display epitopes that resemble a1 since: (a) they were capable of inhibiting 125I-a1 Ig binding to rabbit anti-a1, goat anti-a1, and mouse anti-a1 mAb; and (b) immunization of normal a2a3 rabbits with either anti-Id fraction led to the formation of specific anti-a1 antibody. Reductive cleavage of the anti-Id molecules showed that the a1 determinants in the a2a3- population were fully displayed on isolated H chains, consistent with the presence of latent a1 Ig. On the other hand, as expected for internal images encoded by the antigen-combining site, the a2a3+ anti-Id population required intact H and L chains for maximal a1 expression. The a1-like images within the a2a3+ anti-Id population do not appear to be identical to nominal or latent a1, however, since a2a3- anti-Id was invariably a more efficient inhibitor of a 1 Ig-anti-a1 binding than a a2a3+ anti-Id. These results indicate that immunization with antiallotype can result in the simultaneous production of both latent allotypes and allotypic internal images.

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