Are "hidden" genes for immunoglobulin allotypes of rabbit heavy and light chains expressed upon hyperimmunization?

B cell and antibody repertoire development in rabbits: the requirement of gut-associated lymphoid tissues

The antibody repertoire of rabbits has interested immunologists for decades, in part because of the ease with which large quantities of high affinity antibodies can be obtained in serum, and in part because of the presence of genetic variants, allotypes, within V(H), C(H) and C(L) regions. Studies of these allotypes led to the initial descriptions of allelic exclusion, and neonatal suppression of serum Ig production (allotype suppression), and were instrumental in demonstrating that V and C regions are encoded by separate genes and are usually expressed in cis. The immune system of rabbit continues to be of interest primarily because of the use of both gene conversion and somatic hypermutation to diversify rearranged heavy and light chain genes and the role that gut-associated lymphoid tissues (GALT) and intestinal flora play in developing the primary (preimmune) antibody repertoire.

The structural and genetic basis for expression of normal and latent VHa allotypes of the rabbit

The immunoglobulin heavy chain variable regions of the rabbit are unusual in having genetically controlled, serologically detectable alternative forms, the VHa allotypes, as well as minor VH allotypes of the x, y and w groups. New insights into the probable structural basis for the VHa allotypes have come from re-examination of earlier protein sequence data in the light of newly deduced protein sequences derived from sequencing cloned cDNAs and genomic DNAs encoding VH regions. Here we review this sequence information, and define the allotype-correlated differences at seven positions in framework region 1 and 10 positions in framework region 3 that may lead to the serologically detectable allotypic determinants (allotopes). Most alternative amino acids at allotype-correlated positions can be derived from each other by single-base changes. Thus somatic mutations and/or gene conversion-like events must be considered along with other serological and genetic explanations for various reported observations of the production of latent VHa allotypes. The proximity of rabbit VH genes (approximately 3 kb apart) might enhance the likelihood of conversion-like events in both germline and somatic cells.

The immunomodulatory effect of anti-Micrococcus luteus antibodies. I. Effect on in vitro rabbit T cell functions

A range of purified rabbit anti-Micrococcus luteus antibodies (anti-MCAb) were tested for their ability to interfere with a variety of in vitro immune responses. Such antibodies strongly inhibited the secondary IgG antibody response to sheep red blood cells without affecting the IgM response or the proliferative responses to mitogens and antigens. By exposing lymphocyte populations to anti-MCAb, it was found that such reagents exerted a strong mitogenic effect on rabbit T lymphocytes, provided these cells were derived from antigen-activated lymph nodes. This mitogenic effect was also obtained with F(ab')2 fragments of anti-MCAb and with hybridoma-derived anti-MCAb. Collectively, these data indicate that anti-MCAb inhibit the initiation of IgG synthesis possibly through the expansion of immunoregulatory T cell subsets.

Messenger RNA from allotype-defined rabbits directing the cell-free synthesis of immunoglobulin heavy and light chains

In vitro synthesis studies were performed utilizing polyA(+)-RNA and lymphocytes from the spleens of rabbits hyperimmunized with Micrococcus luteus or Streptococcus pneumoniae (type III). PolyA(+)-RNA isolated after 4 M guanidinium thiocyanate extraction and oligo(dT)-selection appeared to be undegraded on CH3HgOH-agarose gel electrophoresis and demonstrated biological activity when translated in a rabbit reticulocyte cell-free system. The electrophoretic patterns of the specifically immunoprecipitated cell-free products were compared with those of Nonidet-P40 extracts (lysates) and secretions (supernatants) from rabbit spleen lymphocyte cultures and serum proteins. Kappa light chains with specific b allotypes, as well as immunoglobulin heavy chains, were identified. The efficient translation of mRNA of defined allotypes was a necessary prerequisite for production of characterized cDNA clones and identification of genomic sequences for rabbit immunoglobulin heavy and light chains.

Isolation and characterization of IgG molecules expressing latent group b allotypes from pedigreed b4b4 rabbits

Latent group b markers were detected in sera, in IgG preparations, and on isolated L chains from rabbits bred for homozygosity at the b locus. Serologic analysis of sera from an extended family of homozygous b4 rabbits revealed the presence of latent b allotypes in 5 of 37 sera tested. Latent b5 and b9 markers were identified; none of the sera tested contained latent b6. In two instances, the level of latent b9 allotypes was sufficiently high to permit isolation and detailed serologic characterization of the immunoglobulin population bearing this allotype. The fact that latent allotypes were detected in pedigreed homozygous rabbits minimizes the possibility that lymphoid cell chimerism is involved in latent allotype expression. Furthermore, characterization of the b9 IgG population indicates that the latent allotypic determinants do not reside on a subset of molecules with dual allotypic reactivity.

Allelic exclusion in the B lineage cells of the rabbit

Allelic exclusion of the K polypeptide chain allotypes b4 and b5 of the rabbit exists for the immunoglobulins of almost all plasma cells and of most mature small B lymphocytes. However, both these alleles are expressed simultaneously in rare plasma cells and in an usually large fraction of the lymphoid cells of the bone marrow. Our experiments support the idea that such bone marrow B lineage cells do not always show allelic exclusion.