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DNA-binding antibodies from viable motheaten mutant mice: implications for B cell tolerance
C M Westhoff1, A Whittier, S Kathol
1School of Biological Sciences, University of Nebraska, Lincoln 68588, USA.
Abstract:
C57BL/6 me(v)/me(v) (viable motheaten) mice have defective hemopoietic cell protein-tyrosine phosphatase (HCP, SHP-1) and are a model in which to study the role of this phosphatase in immune regulation and hemopoietic development. Immune defects in these mice include hypergammaglobulinemia, production of multiple autoantibodies, and glomerular nephritis. The presence of self-reactive Abs in these mice is an enigma, since it has been demonstrated that they have increased negative selection against self-reactive transgenic Abs. It was of interest to examine autoantibodies from these mice to identify reactivity or structural features that might account for their persistence and expansion in the repertoire. Abs to DNA were selected for investigation, since they have been characterized extensively from normal and autoimmune strains of mice. Viable motheaten mice had high titers of IgM, anti-dsDNA Abs, and all 12 anti-DNA hybridomas generated were also IgM. They had high avidity for dsDNA, also bound to ssDNA, but were not polyreactive. They used V(H) and V(L) gene families found in anti-DNA Abs from other strains, which reinforces evidence that there is preferential use of a restricted number of germline elements in anti-DNA Abs. The results indicate that Hcph-mutant mice do not delete DNA-reactive B cells, nor are they able to maintain these B cells in a state of anergy. Evidence for positive selection and clonal expansion after V-D-J rearrangement was also seen, in that several Abs expressed the same heavy chain in combination with different light chains, which is also a hallmark of the autoimmune anti-DNA response.
Insights
Viable motheaten mice with defective SHP-1 phosphatase exhibit autoantibodies against DNA. These mice fail to eliminate self-reactive B cells, leading to their expansion and contributing to autoimmune responses.
Area of Science:
- Immunology
- Molecular Biology
- Genetics
Background:
- C57BL/6 me(v)/me(v) mice possess a deficiency in hemopoietic cell protein-tyrosine phosphatase (HCP, SHP-1), serving as a model for immune regulation and hematopoietic development.
- These mice display immune abnormalities, including hypergammaglobulinemia, autoantibody production, and glomerulonephritis.
- The persistence of self-reactive antibodies in these mice is paradoxical, given evidence of enhanced negative selection against such antibodies.
Purpose of the Study:
- To investigate the reactivity and structural characteristics of autoantibodies in viable motheaten mice.
- To understand the mechanisms behind the persistence and expansion of self-reactive antibodies, particularly anti-DNA antibodies.
- To explore the role of SHP-1 deficiency in B cell selection and autoimmune disease development.
Main Methods:
- Generation and characterization of anti-DNA hybridomas from viable motheaten mice.
- Analysis of antibody isotypes (IgM), avidity for double-stranded DNA (dsDNA) and single-stranded DNA (ssDNA).
- Examination of immunoglobulin variable region gene usage (V(H) and V(L) gene families) and evidence of clonal expansion.
Main Results:
- Viable motheaten mice exhibit high titers of IgM anti-dsDNA antibodies, with all generated hybridomas also being IgM.
- These antibodies demonstrate high avidity for dsDNA and also bind ssDNA, but are not polyreactive.
- Analysis revealed preferential use of specific V(H) and V(L) gene families, common in anti-DNA antibodies from other mouse strains.
- Evidence of positive selection and clonal expansion was observed, with shared heavy chains across different light chains in several antibodies.
Conclusions:
- Viable motheaten mice, despite SHP-1 deficiency, do not effectively delete DNA-reactive B cells.
- These mice are unable to maintain DNA-reactive B cells in an anergic state, facilitating their survival and expansion.
- The findings suggest that defective SHP-1 signaling contributes to the autoimmune anti-DNA response through impaired B cell tolerance mechanisms.
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