SUMMARY Rabbits homozygous at the Ab kappa chain allotypic locus (Ab4/Ab4 and Ab9/Ab9) were immunized with negatively and positively charged antigens. The negatively charged antigens were bovine serum albumin (BSA; pI = 4.9), ovalbumin (OV; pI = 4.9) and two synthetic polypeptides: copolymer L‐glutamic acid L‐tyrosine (abbreviated TG; pI = 4.8) and multichain poly (L‐tyrosine: L‐glutamic acid) poly D‐alanine: poly L‐lysine (poly L‐lysine backbone) (abbreviated (TG) ‐ AL; pI = 4.8). The positively charged antigen was hen egg lysozyme (LYS; pI = 10.2). Homozygous Ab9 rabbits responding to negatively charged antigens made less antibody than did Ab4 homozygotes. In contrast, both groups of animals responded equally well to positively charged lysozyme. The relative electric charges of the antibodies were assessed by Sephadex A‐50 chromatography. The charge distribution was found to depend on the charge of the eliciting antigen. The positively charged antibodies of Ab9/Ab9 rabbits were not nearly as positively charged as those raised in Ab4/Ab4 rabbits. The difference in average electric charges and in the range of these charges between Ig Ab4 and Ig Ab9 explain quantitative differences in antibody formation in response to negatively charged antigens and may be a contributing factor to the ‘pecking order’, i.e. unequal phenotypic expression of ligh chain genes in Ab4/Ab9 heterozygotes.

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Summary Immunoglobulin was obtained from a hybridoma cell line, which was a reclone of a hybrid between a rabbit cell and mouse myeloma cell (X63‐Ag8). The immunoglobulin, isolated from the cell culture medium was found to be homogeneous by isoelectrofocusing and immunoelectrophoresis and consisted of mouse heavy and rabbit light chains, linked by disulphide bonds. All immunoglobulin molecules carried both mouse and rabbit determinants; mouse determinants were associated only with the heavy chains while rabbit determinants were only associated with the light chains. The rabbit light chains were of Ab4 allotypical specificity, but possess only some of the Ab4 determinants normally present in Ab4/Ab4 animals. It was sugested that the restriction in allotypical specificity may be a general property of light chain Ab allotypes; the normal serum immunoglobulins may be heterogeneous with respect to the allotypic determinants and any one molecule may possess only a proportion of determinants detected by a conventional anti‐allotype antiserum.

Evidence is provided for the existence of the Fbbas (Basilea) gene product (allotype). Specific antisera were raised by immunization of rabbits that did not possess the Basilea genes. With the help of these antisera, the Basilea allotype was detected in sera from rabbits, homozygous and heterozygous with respect to Basilea gene. The Basilea gene is expressed on a very low proportion of immunoglobulin molecules. The isoelectric point of the Basilea light chains is distinct from that of the lambda-light chains (peaks at pH 4.7 and 5.5, respectively). Sera from a large proportion of Ab9-positive rabbits of the Basel Institute for Immunology that were heterozygous at the Ab locus reacted with the anti-Basilea serum, even though they could no possess the Basilea gene at the Ab locus. Sera from Ab9-positive rabbits from Toronto were Basilea-negative. It was suggested that Ab9 and Basilea allotypes are controlled at closely linked loci. Ab9 haplotype prevalent in the Basel animal colony, possesses both Ab9 and Basilea genes, whereas the corresponding Toronto haplotype has only the Ab9, but not Basilea gene. The formation of the Basilea genotype was attributed to a crossing over, during which the Ab9 and Basilea genes separated.