Presence of kappa 2 light chain in normal rabbits and as induced auto anti-allotype antibody in kappa 1 light chain suppressed subjects

Generating the antibody repertoire in rabbit

We describe a model for B cell development and generation of the antibody repertoire in rabbits. In this model, B cells develop early in ontogeny, migrate to GALT, and undergo the first round of diversification by a somatic gene conversion-like process and by somatic mutation. We designate the repertoire developed by this mechanism as the primary antibody repertoire and it is this repertoire that makes the rabbit immunocompetent. We invoke GALT as the site for development of the primary repertoire because (1) surgical removal of GALT from neonatal rabbits results in highly immunocompromised animals, (2) in germfree rabbits essentially no lymphoid development occurs in GALT and the rabbits are immunoincompetent, and (3) the follicular development of rabbit GALT is highly similar to that of the chicken bursa, the site in which the primary antibody repertoire develops by somatic gene conversion in chicken. We suggest that once the primary antibody repertoire is formed, it is maintained by self-renewing CD5+ B cells and is expanded to a secondary antibody repertoire after the B cells encounter antigen.

In utero suppression of kappa 2 isotype in homozygous bas/bas rabbits through embryo transfer

Allotypes of rabbit Ig provide a useful tool for the study of quantitative expression of alternative allelic forms. In the rabbit, maternal Ig is transmitted to the foetus and protects the immunologically immature newborn during several of the first weeks of life. Induced maternal antibodies directed towards a paternally inherited allotype of the offspring can influence the expression of that allotype drastically. Normal Ig level in heterozygous allotype suppressed animals is provided by increased expression of the alternative allele. On the other hand, allotype suppression in homozygous animals leads to increased expression of non-allelic alternative gene products. We quantitatively analysed the expression of bas, a marker on the kappa 2 light chain isotype of the mutant strain Basilea, in homozygous bas/bas rabbits which had been fostered in utero of b4/b6 mothers producing anti-bas. All of the offspring studied expressed the kappa 2 isotype at a very low level at two months of age, and, in some individuals, bas was hardly expressed after 6 to 12 months. A suppressed rabbit, which was immunized to produce auto-antibodies against bas, continued to do so for at least 2.5 years. The long duration of homozygous bas suppression contrasts with homozygous suppression of other allotypes (CL kappa 1 and VHa) which generally lasts for a much shorter period.

Organization and structure of wild rabbit kappa2 genes: implications for regulation of kappa expression

In domestic populations, the rabbit kappa light chains are known to be encoded by two loci which are unequally expressed. The kappa1 chains account for the majority of total serum kappa chains, and display an unusual complex polymorphism. In order to study the evolution and the putative correlations between the expression, the organization and the structure of the kappa genes, we analysed the kappa loci in wild rabbit populations. The kappa genes of b95, b97 and b98 allotypes are organized in two loci similar to that of domestic rabbits. The structure of the constant region of the kappa2 locus was determined from a wild rabbit which expresses b95 allotype kappa1 chains. The Ckappa2bas2 of b95 displays a single silent mutation when compared to Ckappa2bas2 associated with b4 and one amino acid change relative to Ckappa2bas1 chain. Therefore, in contrast to the kappa1 locus, the constant regions of the kappa2 locus display strong conservation during evolution. A model based on conformation of the kappa chains is discussed to explain the evolution and expression of the two kappa loci.

Mapping of the duplicated rabbit immunoglobulin kappa light chain locus

The rabbit has two isotypic forms of the immunoglobulin kappa light chain, K1 and K2, which probably arose by duplication. In the normal rabbit, only traces of K2 light chains are produced. However, K2 levels are elevated in allotype-suppressed rabbits and in the Basilea strain which does not produce K1 because of a K1 mRNA splice site mutation. Previous cloning and sequencing showed that each isotype has its own set of J kappa genes but it was not known whether the two isotypes utilize shared or separate sets of V kappa genes. In addition, although genetic linkage of allotypes associated with the K1 and K2 genes has been demonstrated, physical linkage had not been previously demonstrated by overlapping cosmid or phage clones. We used pulsed field and transverse alternating field electrophoresis to obtain megabase maps and to estimate the size of the duplication of the rabbit kappa light chain locus. We found that the two C kappa genes are about 1 megabase apart. One explanation for the poor expression of K2, could be great physical distance from V kappa genes. However, we found that there are V kappa, J kappa and C kappa 2 genes within a approximately 105-kb fragment. Thus, physical distance of V kappa from C kappa 2 may not be the basis for poor K2 expression.

The intrathecal immune response in multiple sclerosis: a different concept of 'specificity'

A hypothesis is presented in which the immune response in multiple sclerosis is conceived as a primary response to an auto-antigen located within the immune system (e.g. a certain allotype or HLA epitope) which shows subsequent or simultaneous specificity for a greater number of nominal antigens [corrected]. The increased tendency of [corrected] such antibodies to self-aggregation might play a critical role in the pathogenesis.

Rearrangement of the immunoglobulin kappa light chain genes in a b4 rabbit and a Basilea rabbit

The immunoglobulin chi light chain gene family of the rabbit is characterized by the presence of two constant region exons, C chi 1 and C chi 2 encoded at the chi 1 and chi 2 loci, and linked to their own cluster of joining pieces (J chi). The gene segments at the two loci are very unequally expressed. Thus, in domestic rabbits, the immunoglobulin light chains are essentially of the chi 1 type, even though the gene segments at the chi 2 locus are structurally functional. We have investigated the origin of the weak expression of the genes at the chi 2 locus by analysing the pattern of rearrangement of the chi 1 and chi 2 J chi segments in rabbit B-cell populations. Southern blot analysis of B cells isolated from a rabbit expressing chi 1 light chains suggests that the genes at the chi 2 locus underwent very few, if any, rearrangements. However, using more sensitive approaches, it was possible to detect transcripts originating from the rearranged chi 2 locus. In contrast, in B cells isolated from a Basilea rabbit, which cannot express chi 1 chains, Southern blots revealed the rearrangement of the chi 2 genes, whereas the chi 1 rearranged fragments were barely detectable. These results could be explained either by preferential rearrangement of genes at the chi 1 locus or by clonal amplification of only cells producing chi 1. Furthermore, results of Southern blot analysis provide evidence that V-J recombination may be accompanied by an inversion of the intervening DNA region.

Linked genetic markers of the rabbit kappa light chain are not linked to the Tcr beta chain genes

In order to investigate linkage, we used serum allotypes of the two rabbit C kappa isotypes and restriction fragment length polymorphisms (RFLPs) of the genes for V kappa, C kappa, and T-cell receptor C beta. The inheritance of these genetic markers was studied through backcross and F2 matings. Southern analysis and hybridization of genomic DNA with a C kappa probe detected a 5 kb Pst I fragment linked to expression of the K2bas1 allotype and the presence of the kappa 1bbas gene and a 6.6 kb Pst I fragment linked to the expression of the K1b9 allotype, the presence of the kappa 2bas2 gene and lack of expression of the K2bas1 allotype. A V kappa probe detected a 1.3 kb Eco RI fragment linked to the presence of the kappa 1bbas gene and expression of the K2bas1 allotype. In contrast, the 9 or 14 kb Eco RI RFLP (C beta a or C beta b) detected with a Tcr beta chain probe segregated independently from C kappa allotypes and RFLPs. It has previously been found that C kappa and C beta are also unlinked in man, whereas in the mouse they are linked at a distance of approximately 8 centimorgans.

Expression of K2 isotype mRNA in normal and Basilea rabbits

Molecular genetic techniques were used to study the regulated expression of the kappa light chains in the rabbit. Two isotypic kappa genes, kappa 1 and kappa 2, have been identified in the genome of all rabbits; however, the majority of secreted immunoglobulins produced by most domestic rabbits bear only K1 light chains. S1 nuclease protection experiments utilizing a single-stranded cDNA probe encoding the K2 constant region were performed to identify K2 mRNA in normal rabbits and in the mutant Basilea rabbit strain in which K2 light chains were first described. Varying amounts of K2 message were observed in the non-Basilea samples, between 0.05-1% of the K2 RNA found in a comparable preparation of Basilea RNA. Evidence for alternatively spliced messages was also noted. In addition, a K2 oligonucleotide probe is described which will distinguish between the K2 allotypic forms, bas1 and bas2.

Escape from b locus allotype suppression in the rabbit is mediated by IgM molecules bearing an allotope-restricted variant of kappa light chain

Rabbits homozygous for b6 at the kappa light chain b locus were suppressed for the expression of the b6 allotype and then induced to produce auto anti-b6 antibody. Rabbits which subsequently escaped suppression produced auto antibody with restricted allotype specificity. Escape from allotype suppression was mediated by IgM bearing a kappa chain variant with a restricted number of b6 allotopes and having a diminished interaction with auto anti-b6 antibodies from the same and other rabbits escaping b6 suppression. This suggested that there were allelic variants or subpopulations of the b6 light chain which were under independent regulation of expression, clearly influenced by the specificity of auto anti-allotype antibody. Since escape from suppression was mediated by IgM it is proposed that a normal pathway of B cell differentiation occurs during recovery from suppression.