Cross-reaction of a Minor Variant of the A1 Allotypic Specificity with Anti-a2 Antibodies

Certain samples of hare IgG can combine with cross-linked anti-a2 antisera prepared in the a3/a3 rabbit. This cross-reaction permitted the isolation, on hare IgG immunoadsorbent, of anti-a2 cross-reacting antibodies (anti-a2(Lv) antibodies). The binding of labeled rabbit a2 IgG to insolubilized anti-a2(Lv) antibodies is inhibited by a1 IgG, demonstrating a cross-reactivity with a2. The percentage of a1 IgG cross-reacting with anti-a2 antiserum (a1(2) IgG) is about 0.5% of total a1 IgG. The a1(2) molecules represent another variant (or set of variants) of the a1 specificity. Demonstration of this variant of a1 IgG brings to seven the minimum number of described a1 variants, and its low concentration among a1 IgG (0.5%) is in favor of a larger number of variants of allotypic specificities. Arguments in favor of common ancestor genes for allotypy in lagomorphs are given.