Immunoglobulin (Ig) gene class-switch DNA recombination (CSR) and somatic hypermutation (SHM), which requires activation-induced cytidine deaminase (AID), underpins autoantibody class-switching from the non-harmful, protective IgM class to the potentially pathogenic IgG and IgA classes. CSR replaces the Ig heavy chain (IgH) constant (CH) region, e.g., Cμ of IgM, with Cγ, Cε or Cα, thereby producing IgG, IgE or IgA antibodies. Aberrant CSR results in a variety of diseases, including atopic IgE reactions (e.g., in asthma), hyper-IgM syndrome, and systemic or organ-specific autoimmunity.
I have explored the in-depth molecular mechanisms underlying antibody class-switching to IgG, IgA or IgE, with emphasis on the targeting and induction of CSR factors. Our work seeks to establish a paradigm that intervention at any of these two levels of regulation can modulate class-switching. Such a paradigm will be critical in shaping research in vaccines, whose efficacies depends on generation of high-affinity antibodies and on therapeutics to inhibit unwanted class-switching in a variety of clinical conditions. We first explored CSR inhibition mechanisms by quantifying direct interaction between 14-3-3, AID, PKA or Ung and viral protein R (Vpr). As we have shown in activated B cells, 14-3-3 adaptors specifically recruit AID on IgH switch (S) region DNA. Our research has been focused on using a naturally occurring viral protein R (Vpr) to disrupt 14-3-3-mediated recruitment of the AID-centered CSR machinery to S region DNA, which inhibited CSR. We then focused on using a small molecule compound for therapeutic treatment in preventing high titers of autoantibodies in systemic lupus erythematosus (SLE). MRL/Faslpr/lpr mice treated with CID 1067700, the only known inhibitor of Rab7, displayed reduced decreased glomerular hypercellularity and proteinuria, virtually abolished skin lesions, and extended life span. Accordingly, serum titers of anti-dsDNA IgG1, IgG2a, IgG2b and IgG3 autoantibodies were reduced in treated mice, in association with reduced generation of IgG+ B cells. These mice, however, showed increased proportion of IgM+ B cells, but normal proportions of CD4+ and CD8+ T cells as well as CD138+ plasma cells. These together with reduced AID expression in treated mice indicates that CID 1067700 selectively inhibits B cell class-switching. Indeed, the CID 1067700 treatment blunted the antibody response NP-LPS, a T cell-independent antigen, and inhibited CSR to IgG1 and IgA in purified B cells in vitro, but did not affect B cell proliferation, survival or differentiation into plasma cells. Overall, our data have further confirmed the specific role of Rab7 in mediating AID expression and CSR, and strongly suggest Rab7 as a therapeutic target for systemic lupus.