Identification of novel VH1/J558 immunoglobulin germline genes of C57BL/6 (Igh b) allotype

A unique mouse strain that develops spontaneous, iodine-accelerated, pathogenic antibodies to the human thyrotrophin receptor

Abs that stimulate the thyrotropin receptor (TSHR), the cause of Graves' hyperthyroidism, only develop in humans. TSHR Abs can be induced in mice by immunization, but studying pathogenesis and therapeutic intervention requires a model without immunization. Spontaneous, iodine-accelerated, thyroid autoimmunity develops in NOD.H2(h4) mice associated with thyroglobulin and thyroid-peroxidase, but not TSHR, Abs. We hypothesized that transferring the human TSHR A-subunit to NOD.H2(h4) mice would result in loss of tolerance to this protein. BALB/c human TSHR A-subunit mice were bred to NOD.H2(h4) mice, and transgenic offspring were repeatedly backcrossed to NOD.H2(h4) mice. All offspring developed Abs to thyroglobulin and thyroid-peroxidase. However, only TSHR-transgenic NOD.H2(h4) mice (TSHR/NOD.H2(h4)) developed pathogenic TSHR Abs as detected using clinical Graves' disease assays. As in humans, TSHR/NOD.H2(h4) female mice were more prone than male mice to developing pathogenic TSHR Abs. Fortunately, in view of the confounding effect of excess thyroid hormone on immune responses, spontaneously arising pathogenic human TSHR Abs cross-react poorly with the mouse TSHR and do not cause thyrotoxicosis. In summary, the TSHR/NOD.H2(h4) mouse strain develops spontaneous, iodine-accelerated, pathogenic TSHR Abs in female mice, providing a unique model to investigate disease pathogenesis and test novel TSHR Ag-specific immunotherapies aimed at curing Graves' disease in humans.

Crystal structure of two anti-porphyrin antibodies with peroxidase activity

We report the crystal structures at 2.05 and 2.45 Å resolution of two antibodies, 13G10 and 14H7, directed against an iron(III)-αααβ-carboxyphenylporphyrin, which display some peroxidase activity. Although these two antibodies differ by only one amino acid in their variable λ-light chain and display 86% sequence identity in their variable heavy chain, their complementary determining regions (CDR) CDRH1 and CDRH3 adopt very different conformations. The presence of Met or Leu residues at positions preceding residue H101 in CDRH3 in 13G10 and 14H7, respectively, yields to shallow combining sites pockets with different shapes that are mainly hydrophobic. The hapten and other carboxyphenyl-derivatized iron(III)-porphyrins have been modeled in the active sites of both antibodies using protein ligand docking with the program GOLD. The hapten is maintained in the antibody pockets of 13G10 and 14H7 by a strong network of hydrogen bonds with two or three carboxylates of the carboxyphenyl substituents of the porphyrin, respectively, as well as numerous stacking and van der Waals interactions with the very hydrophobic CDRH3. However, no amino acid residue was found to chelate the iron. Modeling also allows us to rationalize the recognition of alternative porphyrinic cofactors by the 13G10 and 14H7 antibodies and the effect of imidazole binding on the peroxidase activity of the 13G10/porphyrin complexes.

Structure-function analysis and molecular modeling of DNase catalytic antibodies

There is great interest in the antibodies-to-DNA transformation, since this change is characteristic of autoimmune diseases and contributes to its pathology. After immunization and fusions, 14 hybridomas bearing DNA-hydrolysis activity against pUC19 plasmid DNA were obtained. Genes coding for V_H and V_L regions of the 14 monoclonal antibodies (mAbs) were cloned and sequenced. The sequences were compared with sequences of the Ig-Blast database to determine their germline and to identify potential mutations responsible for DNA binding and DNase activity. V genes of the H chains’ genes expressed four genes of the V_H1/J558 family, three of V_H5/V_H7183, and three of V_H8/V_H3609. The genetic repertoire of these mAbs was examined by determining the nucleotide sequences of their H chain V regions. This V_H and V_L domain was most similar to an anti-ssDNA (DNA-1) antibody as well as to catalytic autoimmune mAb (m3D8). Computer-generated models of the three-dimensional structures of V_H and V_L (VHL4) of the IgG4 combinations were used to define the positions occupied by the important sequence motifs at the binding sites. The modeling structure showed that VHL4 binds to oligo (dT3) primarily by sandwiching thymine bases between Tyr L32, Tyr L49 and Tyr H97 side-chains. Superposing VHL4 with anti-nucleic acid m3D8 catAbs revealed a common ssDNA recognition module consisting of His L93, His H35 residues which are critical for DNA-hydrolyzing antibodies. This study demonstrates the potential usefulness of the protein DNA surrogate in the investigation of the origin of anti-DNA antibodies’ hydrolyzing activities.

Genetic variation in C57BL/6 ES cell lines and genetic instability in the Bruce4 C57BL/6 ES cell line

Genetically modified mouse strains derived from embryonic stem (ES) cells are powerful tools for gene function analysis. ES cells from the C57BL/6 mouse strain are not widely used to generate mouse models despite the advantage of a defined genetic background. We assessed genetic variation in six such ES cell lines with 275 SSLP markers. Compared to C57BL/6, Bruce4 differed at 34 SSLP markers and had significant heterozygosity on three chromosomes. BL/6#3 and Dale1 ES cell lines differed at only 3 SSLP makers. The C2 and WB6d ES cell lines differed at 6 SSLP markers. It is important to compare the efficiency of producing mouse models with available C57BL/6 ES cells relative to standard 129 mouse strain ES cells. We assessed genetic stability (the tendency of cells to become aneuploid) in 110 gene-targeted ES cell clones from the most widely used C57BL/6 ES cell line, Bruce4, and 710 targeted 129 ES cell clones. Bruce4 clones were more likely to be aneuploid and unsuitable for ES cell-mouse chimera production. Despite their tendency to aneuploidy and consequent inefficiency, use of Bruce4 ES cells can be valuable for models requiring behavioral studies and other mouse models that benefit from a defined C57BL/6 background.

B7 and 34B7 Monoclonal Antibodies: A Theoretical Approach to the Molecular Basis of Immunoglobulin Cross-Reactive Antibodies

Neonatal natural antibodies (NAbs) are characterized by their high degree of idiotypic cross reactivity, together with some restrictions in the genetic mechanisms of variable region diversity. We report here the immunogenetic analysis of two anti-idiotype antibodies (B7 and 34B7 monoclonal antibodies [MAbs]), which are also polyreactive as NAbs. Evidence of a process of somatic mutations were found for heavy and light chain variable regions of both antibodies. A phylogenetic analysis of the V(H)J558 family showed that the immunoglobulin cross-reactivity displayed by B7 and 34B7 MAbs is not restricted to a particular subgroup of this family. Moreover, we identified amino acid motifs in the CDR H1 and H2 of B7 and 34B7 MAbs that are also present in high proportion in immunoglobulin cross-reactive antibodies (ICRA) reported in the Kabat database. We propose that these regions are involved in ICRA activity.

B cell receptors in TCL1 transgenic mice resemble those of aggressive, treatment-resistant human chronic lymphocytic leukemia

B cell chronic lymphocytic leukemia (B-CLL) is a clonal overgrowth of CD5(+) B lymphocytes. In this disease, the B cell antigen receptor (BCR) is intimately linked to disease severity, because patients with BCRs, comprised of unmutated V(H) genes, follow a much more aggressive course. This and related observations suggest that B-CLL derives from a B cell subset comprised of restricted BCR structural diversity and that antigen-selection and drive are major factors promoting the disease. Nevertheless, the initiating event(s) that lead to the development of B-CLL are still unclear, in part because of the lack of an animal model that spontaneously evolves the molecular abnormalities that occur in the human disease. Because overexpression of the TCL1 gene in murine B cells leads to a CD5(+) B cell lymphoproliferative disorder with many of the features of human B-CLL, we studied leukemias emerging in these mice to examine the extent to which their BCRs resemble those in B-CLL. Our data indicate that the immunoglobulin heavy and light chain rearrangements in TCL1 mice display minimal levels of somatic mutations and exhibit several molecular features found in the human disease. Like human B-CLL, TCL1 leukemic rearrangements from different mice can be very similar structurally and closely resemble autoantibodies and antibodies reactive with microbial antigens. Antigen-binding analyses confirm that selected TCL1 clones react with glycerophospholipid, lipoprotein, and polysaccharides that can be autoantigens and be expressed by microbes. This (auto)antigen-driven mouse model reliably captures the BCR characteristics of aggressive, treatment-resistant human B-CLL.