Fine specificity and heavy chain V gene usage of antibodies to the phosphorylcholine hapten

Sterile inflammation in the spleen during atherosclerosis provides oxidation-specific epitopes that induce a protective B-cell response

The B-cell response in atherosclerosis is directed toward oxidation-specific epitopes such as phosphorylcholine (PC) that arise during disease-driven oxidation of self-antigens. PC-bearing antigens have been used to induce atheroprotective antibodies against modified low-density lipoproteins (oxLDL), leading to plaque reduction. Previous studies have found that B-cell transfer from aged atherosclerotic mice confers protection to young mice, but the mechanism is unknown. Here, we dissected the atheroprotective response in the spleen and found an ongoing germinal center reaction, accumulation of antibody-forming cells, and inflammasome activation in apolipoprotein E-deficient mice (Apoe(-/-)). Specific B-cell clone expansion involved the heavy chain variable region (Vh) 5 and Vh7 B-cell receptor families that harbor anti-PC reactivity. oxLDL also accumulated in the spleen. To investigate whether protection could be induced by self-antigens alone, we injected apoptotic cells that carry the same oxidation-specific epitopes as oxLDL. This treatment reduced serum cholesterol and inhibited the development of atherosclerosis in a B-cell-dependent manner. Thus, we conclude that the spleen harbors a protective B-cell response that is initiated in atherosclerosis through sterile inflammation. These data highlight the importance of the spleen in atherosclerosis-associated immunity.

The 1F7 idiotype is selectively expressed on CD5+ B cells and elevated in chronic hepatitis C virus infection

Antibodies against different chronic viruses, including hepatitis C virus (HCV), express a public cross-reactive idiotype (Id) designated as 1F7. The prominence of this Id may reflect selective engagement of B1 B cells by chronic pathogens. We investigated this by comparing 1F7 Id expression on CD5(+) and CD5(-) B cells, total IgG, total IgM and anti-HCV core antibodies in different HCV exposure settings. By flow cytometry, we observed a selective increase in 1F7 Id(+)CD5(+) B cells in chronic HCV infection. 1F7 Id levels in different immunoglobulin compartments were measured by enzyme-linked immunosorbent assay. 1F7 Id expression was prominent in anti-HCV core antibodies of approximately 90% of 141 HCV-exposed individuals tested. In the Canadian and Armenian study groups, participants who spontaneously cleared HCV infection had lower median 1F7 Id levels on total plasma IgG and anti-HCV core antibodies. Armenian spontaneous clearers, who were younger and more recently infected than their Canadian counterparts, also had had lower median 1F7 Id levels on total plasma IgM. Engagement by HCV of B-cell receptors within, or overlapping with the CD5(+) B1 B-cell repertoire is reflected in the production of 1F7 Id(+) anti-HCV antibodies and expansion of 1F7 Id(+)CD5(+) B cells. Higher 1F7 Id expression levels are associated with chronic infection.

Mouse monoclonal antibodies to pneumococcal C-polysaccharide backbone show restricted usage of VH-DH-JH gene segments and share the same kappa chain

The immunization of BALB/c mice with heat-killed cells of Streptococcus mitis SK598 allowed the rescue of mouse monoclonal antibodies (mAbs) reactive with the pneumococcal cell wall C-polysaccharide backbone. We report for the first time the genetic and molecular characterization of these mAbs, which altogether reflect a typical thymus-independent type 2 immune response. They were isotype-diverse (IgM, IgG1, IgG2b and IgG3). They made use of restricted and scarcely mutated VH-DH-JH combinations, and the same kappa chain, essentially in germ line configuration. Interestingly, this light chain was also found making up part of an anti-phosphorylcholine mAb. These mAbs were not inhibited by phosphorylcholine and related compounds, nor N-acetylneuraminic acid (NANA), nor the Forssman disaccharide; some of them showed limited reactivity with the meningococcal C polysaccharide. Their CDR-H3s do not show any recognizable patterns resembling those found in antibodies to bacterial polysaccharides that have already been characterized.

Anti-nuclear antibody production and autoimmunity in transgenic mice that overexpress the transcription factor Bright

The B cell-restricted transcription factor, B cell regulator of Ig(H) transcription (Bright), up-regulates Ig H chain transcription 3- to 7-fold in activated B cells in vitro. Bright function is dependent upon both active Bruton's tyrosine kinase and its substrate, the transcription factor, TFII-I. In mouse and human B lymphocytes, Bright transcription is down-regulated in mature B cells, and its expression is tightly regulated during B cell differentiation. To determine how Bright expression affects B cell development, transgenic mice were generated that express Bright constitutively in all B lineage cells. These mice exhibited increases in total B220(+) B lymphocyte lineage cells in the bone marrow, but the relative percentages of the individual subpopulations were not altered. Splenic immature transitional B cells were significantly expanded both in total cell numbers and as increased percentages of cells relative to other B cell subpopulations. Serum Ig levels, particularly IgG isotypes, were increased slightly in the Bright-transgenic mice compared with littermate controls. However, immunization studies suggest that responses to all foreign Ags were not increased globally. Moreover, 4-wk-old Bright-transgenic mice produced anti-nuclear Abs. Older animals developed Ab deposits in the kidney glomeruli, but did not succumb to further autoimmune sequelae. These data indicate that enhanced Bright expression results in failure to maintain B cell tolerance and suggest a previously unappreciated role for Bright regulation in immature B cells. Bright is the first B cell-restricted transcription factor demonstrated to induce autoimmunity. Therefore, the Bright transgenics provide a novel model system for future analyses of B cell autoreactivity.

Carrier-specificity of a phosphorylcholine-binding antibody requires the presence of the constant domains and is not dependent on the unique VH49 glycine or VH30 threonine residues

Bacterially-produced antibody fragments, such as single-chain Fv (scFv) which comprises the variable regions of the light (VL) and heavy (VH) chains joined together by a short flexible linker, are useful as diagnostic and therapeutic agents. We previously constructed a scFv fragment from a hybridoma antibody (Mab2) but it unexpectedly lacked the unique carrier specificity of the native antibody. Thus, it bound indiscriminately to various phosphorylcholine (PC)-associated antigens, whereas the hybridoma antibody recognized the PC epitope only in the context of the immunizing antigen. Here, we investigated whether the problem was linker-related by changing the linker composition or by deleting it, but these attempts proved futile. Instead, we have constructed a recombinant Fab fragment of the antibody in bacteria that was carrier-specific. This suggests that constant regions are required for the carrier specificity, which presumably helps to mould the fine structure of the antibody combining site or in stabilizing such a structure. Consistent with this global effect is the finding that replacing specific residues in VH with germ-line residues, namely, VH49 glycine and VH30 threonine, both thought previously to be important for the carrier specificity, had no effect on the carrier specificity of the recombinant Fab.

Antigen dose-dependent predominance of either direct or sequential switch in IgE antibody responses

Priming of CBA/J mice with minute doses of protein antigens (Ag) leads to high IgE antibody (Ab) titres in the immune sera of these animals. In contrast priming with large doses elicits only a marginal production of IgE Ab. In vitro restimulation of spleen cells from animals primed with large doses and lacking in vivo IgE Ab leads to a burst of IgE Ab-forming cells. This in vitro anamnestic response is lacking in mice primed with minute doses of Ag. In order to trace the cellular basis of the in vitro IgE memory response we have extended the analysis of the distribution of Ab isotypes to Ag-primed IgG1-deficient delta 5'S gamma 1 mice. The data presented here must be interpreted as followed. Priming of mice with minute doses of Ag leads to a direct switch from IgM to IgE Ab expression in both strains. These animals have high IgE Ab titres without establishing an IgE memory. The direct switch was verified by polymerase chain reaction and Southern blot analysis of switch circle DNA isolated from Ag-specific B cells of CBA/J mice primed with minute doses of Ag. In contrast to immunization with minute doses, priming with large doses of Ag fails to induce in vivo IgE Ab production in CBA/J and delta 5'S gamma 1 mice but establishes a B epsilon memory in CBA/J mice which involves IgG1-bearing intermediate B cells. In vivo these B epsilon memory cells do not enter the status of IgE Ab-producing cells. In vitro they can be released from this anergy and presumed suppression and develop in an anamnestic response into a large population of IgE Ab-forming B cells. This increase in the number of IgE Ab-producing cells after restimulation in vitro is lacking in delta 5'S gamma 1 mice, apparently because of their inability to generate IgG1-expressing precursor cells. The notion of a sequential switch and an IgG1 intermediate B epsilon memory status is also supported by depletion and inhibition experiments. Elimination of IgG1-expressing B cells in CBA/J mice primed with high doses of Ag prevents the IgE Ab burst after in vitro challenge with Ag. The data further suggest that the two switch pathways are not mutually exclusive and that the Ag dose can decide which pathway is preferentially used.

Structural analysis of a phosphorylcholine-binding antibody which exhibits a unique carrier specificity for Trichinella spiralis

A phosphorylcholine (PC)-binding IgG (Mab2) antibody produced by a hybridoma derived from a BALB/c mouse which had been immunized against Trichinella spiralis was found to bind to the immunizing antigen (TSC) but not to other PC-associated antigens such as pneumococcal antigen (PNC) and PC-conjugated ovalbumin (PC-OVA). Sequence analysis of the protein revealed the presence of a heavy chain (VH) which was very similar (differing in only four amino acids) to that of the M511 myeloma protein, and a light chain (VL) which was completely identical to that of the M167 myeloma protein. Several M511/M167+ proteins, including the prototypic M511 protein and PC-binding proteins of other families (TEPC 15 and W3207), were examined in their binding to the various PC-associated antigens. These were found to be largely indiscriminate although subtle differences were observed for some antigens with some of the antibodies. A comparison of the VH sequences of Mab2 and these proteins revealed that of the differences seen, the single most important substitution in Mab2 which could contribute to the unique specificity of the molecule is the glycine residue at 49H. None of the other proteins, including other PCV-binding proteins published to-date, which utilize the same VH segment (99 in total), has this substitution.

Production of anti-phosphorylcholine antibodies of the T15 idiotype in CBA/N xid mice: investigation of the defect using a T15 immunoglobulin transgene

A notable defect in CBA/N xid mice is their relative inability to make antibodies to phosphorylcholine (PC), particularly those of the T15 idiotype which predominate in the anti-PC responses of immunologically normal mice. To investigate the basis of this defect, we introduced functionally rearranged genes encoding a T15+ PC-binding immunoglobulin G antibody into the germline of these animals. Expression of these genes in the xid cells was observed, shown by the existence of a distinct population of T15+ cells (3 x 10(6)) in the spleen of the transgenic animals, and the presence of PC-binding T15+ IgG antibodies (1-15 micrograms/ml) in the serum. Mixed antibody molecules were also found, however, which were composed of both transgene-encoded and endogenously-derived chains. Existence of the T15+ cells in these animals seemed normal, since these were not depleted (to any great extent) and were immunocompetent as well. The latter was shown by the increased T15+ antibody production in the transgenic animals when stimulated with a PC-associated thymus-independent type 1 (TI-1) antigen and anti-idiotype antibodies, but not with the pneumococcal TI-2 antigen. This is similar to the PC-specific (T15-) responsiveness of normal CBA/N xid mice. Based on these results, we argue that a reason why T15+ antibodies are not normally made by CBA/N xid animals is because T15+ genes are not utilized or, as with any T15+ precursors present, selected for in these animals, in contrast to normal mice where the Lyb-5 or CD5 cells (which are absent in CBA/N xid animals) are known to be specially endowed to make such antibodies.

Specific V gene usage in anti-phosphorylcholine IgE antibodies

Three hybridomas from phosphorylcholine(PC)-KLH immunized BALB/c mice producing IgE antibodies against the PC hapten were investigated for their fine specificity to the hapten and usage of V gene segments in H- and L-chains. All three IgE antibodies recognize the entire azophenyl-PC hapten. They are T15 Id negative and do not bind to the natural PC determinant expressed by the Streptococcus carbohydrate R36A. T15 Id positive IgE antibodies could neither be elicited by immunization in detectable amounts nor generated by the cell fusion technique. By using the Southern blot technique and nucleotide sequence analysis of PCR amplified VHDJH and VLJL rearrangements, we have demonstrated that the three IgE anti-PC hybridomas use the VH1-DSP2-JH2, the VHOX1-DSP2-JH3 or the VH36-60-D-JH2 gene segment combinations for the H chain together with the V kappa 1C-J kappa 1, V kappa 1C-J kappa 2 or V lambda 1-J lambda 1 genes for the L chains. Except for the VH36-60, the same gene segments were found in different combinations in anti-PC antibodies of other Ig classes than IgE. However, high rates of somatic mutations are expressed in both VH1 of the H chain and in V kappa 1C of the L chain. The VH36-60 is expressed in antibodies with the major Id of the azophenyl-arsonate (Ars) response and VHOX1 generally contributes to the phenyl-oxazolone specificity. This suggests that these V genes are involved in the recognition of the azophenyl moiety of the coupled PC hapten. Thus PC-KLH specific IgE antibodies utilize mutated VH1 and/or VH/VL gene segment combinations which are involved in binding of the azophenyl spacer. These IgE are therefore specific for azophenyl-phosphorylcholine, unlike antibodies normally expressed against the Streptococcus PC determinant in mice. The genetic diversity and the high mutation rates indicate that the specific B cells develop later in the immune response. Thus, they represent newly generated specificities of so-called group II anti-PC antibodies and are not isotype-switch descendants from already existing T15 Id positive IgM antibodies.

Production and characterization of a mouse/human chimeric antibody directed against human neuroblastoma

Hybridoma CE7 produces a murine antibody (gamma 1/kappa) which binds to a 190-kDa cell-surface glycoprotein of human neuroblastoma. Because of its tumor specificity, it has been used routinely in clinical pathology to confirm diagnosis of neuroblastoma. We have isolated the gene segments coding for the variable regions of the immunoglobulin H and L chain of this hybridoma. These V genes were used to construct mouse/human chimeric H and L chain genes (gamma 1/kappa) which were then expressed in SP2/0 cells. A cell-binding inhibition assay showed that the specificity of the chimeric CE7 antibody (chCE7) is identical to that of the original CE7. Radioiodinated chCE7 binds to approximately 43,000 sites per neuroblastoma cell with an affinity of 10(10) M-1. In neuroblastoma-bearing nude mice, biodistribution studies with [125I]chCE7 were performed and tumor accumulations of up to 32% of injected dose/g tissue together with low blood and organ uptake were found.

Fine specificity and VJ usage of light chains in antibodies to the phosphorylcholine hapten

In the memory response to the phosphorylcholine hapten (PC) two major groups of anti-PC antibodies with different fine specificities are elicited. Group I antibodies are mainly PC specific, whereas Group II antibodies are comprised of two specificities directed against the phenyl-PC and the phenyl moiety of the PC hapten. The VL gene usage of 17 monoclonal memory anti-PC antibodies were investigated by Southern blot analysis and nucleotide sequencing. Six out of eight Group I memory PC-specific antibodies used the same VK22-JK5 rearrangement as the major T15 primary response idiotype. One expressed a mutated JK1 and one employed another VK22 gene family member. A shift in specificity from PC (Group I) towards phenyl-PC (Group II) was accompanied with the usage of either VK1C-JK1 or VK1A-JK5 rearrangements. The phenyl-specific Group II antibodies expressed the V lambda 1-J lambda 1 L chain rearrangement in combination with VH M141 expressing H chains. In this specific segment of Group II antibodies most mutations were found. Thus four different VL genes were found to contribute to the fine specificity of memory response antibodies to the PC hapten in a clear structure-function relationship. The diversified fine specificity in the memory response derives mainly from the usage of different L chains with particular VJ rearrangements in combination with VH of the dominant initial response clonotype and is not primarily due to mutational events.