Immunoglobulin VH Gene Replacement and Generation of Autoreactive Antibodies

Zhixin (Jason) Zhang, Ph.D.

University of Alabama

Funded in September, 2003: $300000 for 3 years
LAY SUMMARY . ABSTRACT . BIOGRAPHY . SELECTED PUBLICATIONS .

LAY SUMMARY

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How are Autoantibodies Generated in Autoimmune Disease?

This study in patients with the autoimmune disease Systemic Lupus Erythematosus (SLE) will explore whether the alteration of a gene that is involved in antibody formation is implicated in the disease.

Autoimmune diseases like SLE are cases of mistaken identity. Immune system antibodies, made by immune B cells, are part of the body's second line of defense. They learn to recognize a specific foreign invader and attack it whenever it appears. Occasionally, however, antibodies mistakenly identify the body's own tissues as foreign and attack them. In SLE, these errant "autoantibodies" attack several organ systems, causing them to malfunction.

The Alabama researchers recently demonstrated that SLE patients often have alterations in a specific gene, called the VH gene, which is involved in the development of immune B cells. The investigators hypothesize that an abnormal replacement of a section of this gene may cause B cells to create autoantibodies that attack DNA in various body organs, resulting in SLE.

The researchers suspect that this gene alteration occurs as B cells mature in the bone marrow. Alternatively, the error could occur once B cells mature and leave the bone marrow to circulate in the patients' blood. To determine what occurs, the investigators will pursue three steps. First, they will find out whether VH gene alterations are correlated with the disease, by collecting blood from SLE patients and healthy controls and seeing whether only the patients have the altered VH gene in their immune B cells. Next, the investigators will determine whether the patients' immune B cells, containing the altered gene, produce antibodies that react to the patients' own DNA. Thereafter, the researchers will determine whether the gene's alteration occurs in the patients' B cells while these cells are developing in bone marrow or after they have entered the bloodstream. The answers may help to explain how autoimmunity occurs in SLE, and perhaps in other autoimmune diseases as well.

ABSTRACT

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Immunoglobulin VH Gene Replacement and Generation of Autoreactive Antibodies

Production of pathogenic high affinity anti-DNA antibodies is one of the hallmarks of human and murine systemic lupus erythematosus (SLE), but how these autoantibodies are generated is unclear. VH gene replacement has been proposed as one mechanism to delete immunoglobulin heavy chain (IgH) genes that encode self-reactive antibodies. As we recently showed, VH replacement occurs through RAG-mediated recombination involving cryptic RSS within the third framework region of VH gene. It occurs in bone marrow immature B cells during B cell development and contributes significantly to the primary B cell repertoire in humans. Strikingly, VH replacement extends the IgH CDR3 and preferentially introduces charged amino acids.

Unusually long CDR3 regions and overrepresentation of charged amino acids are common features of autoantibodies, and the presence of arginine residues within CDR3 is an important determinant for anti-DNA reactivity. Our preliminary analysis of IgH genes expressed by a subgroup of SLE-associated CD27high plasma cells identified a significantly higher frequency of VH replacement products.

We hypothesize that abnormal VH replacement may contribute to the generation of anti-DNA antibodies and thereby to SLE pathogenesis. We wish to test this hypothesis with the following proposed studies. 1) Examine the potential correlation between VH replacement and SLE. 2) Determine if VH replacement contributes to the generation of anti-DNA antibodies. 3) Determine if abnormal VH replacement occurs in peripheral blood B cells of SLE patients and explore the underlying mechanism.

INVESTIGATOR BIOGRAPHIES

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Zhixin (Jason) Zhang, Ph.D.

Zhixin (Jason) Zhang, University of Alabama Assistant Professor, received his Ph.D. in 1997 from the university in the field of cytokine signaling and transcriptional regulation of fibrinogen gene expression. His initial postdoctoral training was with Dr. S. Louis Bridges, Jr., studying B cell abnormalities in rheumatoid arthritis, and thereafter with Dr. Max D. Cooper, studying molecular regulation of human B cell development and antibody repertoire formation. He joined the Department of Medicine at UAB in May 2003.

His laboratory's long-term interest is to understand the molecular regulation of early B cell development and antibody repertoire formation, which enables antibodies to combat different antigens. His research explores how a diverse antibody repertoire is generated through somatic recombination of previously separated variable (V), diversity (D) (for heavy chain only), and joining (J) gene segments. Currently, the research focuses on two aspects of the molecular regulation of the immunoglobulin gene rearrangement process. The first is to understand the B lineage-specific regulation of immunoglobulin heavy chain gene recombination. The second is to study the molecular basis and regulatory mechanism for VH gene replacement, a process to edit the unwanted V(D)J joints generated during primary immunoglobulin heavy chain gene rearrangement, and its potential correlation with autoimmune diseases.

SELECTED PUBLICATIONS

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Zhang Z.  VH replacement in mice and humans.  Trends Immunol. 2007 Mar;28(3):132-7.

Zhang Z.*, Espinoza C.R., Yu Z., Stephan R., He T., Williams G.S., Burrows P.D., Hagman J., Feeney A.J., and Cooper M.D. Transcription factor Pax5 (BSAP) transactivates the RAG-mediated V(H)-to-DJ(H) rearrangement of immunoglobulin genes. Nat Immunol. 2006 Jun;7(6):616-24.
(*Zhang, co-corresponding author)

Liu Y., Fan R., Zhou S., Yu Z., and Zhang Z.  Potential contribution of VH gene replacement in immunity and disease.  Ann N Y Acad Sci. 2005 Dec;1062:175-81.

Zhang Z., Burrows P.D., and Cooper M.D.  The molecular basis and biological significance of VH replacement.  Immunol Rev. 2004 Feb;197:231-42.