Expression of cross-reacting determinants of the immunoglobulin heavy chain variable region a3 allotype in Oryctolagus and Lepus

Abstract

Two anti-a3 Ab sub-populations, anti-a3-JR Ab and anti-a3-NZW Ab, were isolated from New Zealand White domestic rabbit (NZW) anti-a3 antiserum by sequential affinity chromatography with two immunoadsorbcnt columns, one containing blacktail jackrabbit (JR) ‘a3’ IgG and the other containing NZW a3 IgG. The anti-a3-JR Ab, which represents about 17% of the total anti-a3 Ab, reacted with 100% of the a3 IgG molecules from several NZW rabbits and with 100% of the ‘a3’ IgG molecules from three unrelated jackrabbits and one cottontail rabbit (CT). The anti-a3-NZW Ab reacted with 100% of the a3 IgG molecules from NZW rabbits, but did not react with either the JR or the CT ‘a3’ IgG. These results indicate that the anti-a3-JR Ab reacts with a subset of a3 determinants (a3-JR) which is present on the JR and CT ‘a3’ IgG, and that the anti-a3-NZW Ab reacts with another subset of a3 determinants (a3-NZW) which is not present in the JR or CT ‘a3’ IgG. Both a3-JR and a3-NZW determinants are present in all of the NZW a3 IgG molecules. Moreover, inhibition experiments suggest that the cross-reacting a3 determinants in JR IgG are not identical in structure to those in NZW IgG. However, it is uncertain whether the cross-reactivity of the a3 allotypic specificities is a function of amino acid sequence differences or of differences in three-dimensional configuration due to the association with different light chains in the JR IgG molecules. It is further postulated that a ‘common’ a3 allotypic determinant(s) has evolved unchanged from an ancestral gene(s).