Project 1: Genetic Studies of Lupus

Our understanding of the genetic basis of autoimmunity has been greatly augmented by forward genetic and reverse genetic studies. Forward genetic studies have highlighted several genes as potential candidates for systemic autoimmunity, as portrayed in Figure 1. In parallel, reverse genetic studies in murine and human lupus have uncovered several dozen lupus susceptibility loci (Figure 2). A similar degree of complexity has also been noted in outher autoimmune diseases (Figure 3). In both Figure 2 and Figure 3, murine loci are shown on the left of each chromosome, and the human loci on the right.

The studies in our own laboratory have focused on the genetics of lupus in the SNF1 and NZM2410 murine models. The long-term goals of this project are to understand how these different loci function, as well as to identify the genetic and molecular players that are responsible for disease. These goals are served by the generation and analysis of C57BL/6-based congenic strains bearing the different lupus susceptibility loci.

Project 2: How Lupus Loci Breach Immune Tolerance

It is clear from the study of B6.Sle lupus congenic strains that the different lupus susceptibility loci lead to the formation of different fine-specificities of anti-nuclear antibodies. In other words, these different susceptibility loci have the potential to breach immune tolerance, and to precipitate the generation of anti-self antibodies.

In order to understand how these loci actually breach immune tolerance, they have been bred onto BCR (or Ig) and TCR transgenic models specific for self or foreign antigens. By studying how tolerance to the respective antigens become breached in the context of the different loci, we’re beginning to understand how the delicate balance between tolerance and autoimmunity is tipped in lupus.

Project 3: Genetic Origins of Anti-DNA Abs in Lupus

It is clear that the genesis of pathogenic anti-DNA antibodies in lupus is also polygenic in origin. It appears that at least two distinct genetic players are required.

On the one hand, loci such as Sle1 appear to be important in breaching tolerance to chromatin. However, B6.Sle1 mice exhibit relatively low levels of anti-DNA antibodies despite bearing high titers of anti-chromatin (or anti-nucleosome) antibodies.

On the other hand, players such as Sle3 and FAS-lpr seem to be important in impairing activation-induced cell death; however, this simply leads to low titers of anti-DNA antibodies.

In contrast, the epistatic interaction of both these pathways (e.g., Sle1 + Sle3, or Sle1 + FAS-lpr) leads to high titers of nephrophilic anti-dsDNA antibodies and nephritis. Ongoing studies are aimed at dissecting the molecular pathways leading to the genesis of pathogenic anti-DNA antibodies in lupus, using these novel models.

Project 4: Molecular Origins of Anti-DNA Abs in Lupus

One can perhaps distinguish three different categories of anti-DNA antibodies: anti-ssDNA, anti-dsDNA and anti-nucleosome antibodies. In order to understand if these 3 classes of anti-DNA antibodies have distinct molecular signatures, we have reviewed the heavy chain (Table 2) and light chain usage of all antinuclear antibodies published to date.

Although these comparative studies have yielded valuable insights pertaining to the molecular makeup of anti-nuclear antibodies, they suffer from one important caveat – most comparisons of antinuclear antibodies have been made with non-nuclear binders drawn from totally different strains (with different immunoglobulin haplotypes), and this confounds data interpretation.

In view of this, we have generated large panels of anti-nuclear and non-nuclear antibodies from several lupus strains. This novel bank of antibodies is not only helping to shed light on what the distinctive molecular features of antinuclear antibodies might be, it is also yielding important information concerning the in vivo pathogenicity of these different antibodies.

Finally, single-cell PCR studies of B-cells at different stages of development are helping us understand the precise stage(s) at which anti-nuclear antibodies might arise and expand. Understanding how anti-DNA antibodies arise and how they function to cause disease is critical for future interventional strategies targeting these pathogenic players.

Project 5: Genetics and Immunology of Renal Disease in Lupus

Once anti-DNA antibodies (and several other associated specificities) are formed, these pathogenic antibodies lead to renal damage and failure. Indeed, this is an important cause of morbidity and mortality in this disease. Several findings indicate that one or more lupus susceptibility loci may actually be dictating the degree and nature of end-organ disease. Thus, for example, kidneys of some genotypes may be more susceptible to anti-DNA mediated damage than others.

With respect to this phase of disease, our laboratory is interested in two key questions:

(1) What are the fine-specificities of autoantibodies that are pathogenic?
(2) Are the end-organs (e.g., the kidneys) in lupus intrinsically “abnormal”?

With respect to the first question, we and others have noted that autoantibodies that exhibit in vivo “nephrophilicity” are the most pathogenic. It’s currently not clear as to what these “nephrophilic” autoantibodies actually bind to in the kidneys. With respect to the second question, we have identified several inbred mouse genomes and lupus susceptibility loci that are associated with enhanced (experimentally induced) renal disease. By using unilateral renal transplants, microarray studies and glomerulocyte cultures, we are beginning to unravel the genetic and molecular players dictating renal disease in lupus. Recognizing these cardinal players is a necessary first step for the successful therapeutic modulation of lupus nephritis in the future.