Paul A. Singer

Molecular Genetics of Murine Lupus Models

Publisher Summary The chapter that addresses the Ig germ line gene organization in lupus-prone strains of mice suggested that the disease can develop in different Ig heavy and light chain haplotypes, and that the Ig germ line genes in lupus mice are probably normal. Analyses of the Ig gene segments expressed in monoclonal autoantibodies from autoimmune mice revealed that similar, moreover, in some instances even identical, gene segments are expressed in autoantibodies and in antibodies to exogenous antigens, and that antiself and antiforeign responses are encoded by the same, or at least an overlapping, germ line gene repertoire. Evidence has been obtained that, in an individual lupus mouse, the number of autoantibody-secreting clonotypes decreases after class switch, while that of productive mutations increases, suggesting that antiself responses might be (auto) antigen-driven responses, but this conclusion should be considered tentative. Finally, based on the investigations of I-E and Mls tolerance-related Vβ clonal deletions, the chapter proposes that the abnormally proliferating, autoimmunity-inducing/enhancing double-negative TcR α:β + lpr and gld cells are not related to immature CD4 - 8 - thymocytes, but instead are derived from CD4 + 8 + precursors through a process resulting in down-regulation of both accessory molecules.

T‐Cell Receptor Vβ Repertoire Expression in Murine Models of SLE

T cells may participate in autoimmune disease pathogenesis either directly in the form of cytotoxic T cells, as in several organ-specific autoimmune diseases including insulin-dependent diabetes (Bottazzo et al. 1985), Graves disease (Londei et al. 1985), and multiple sclerosis (Traugott et al. 1983, Hauser et al. 1986); or indirectly as helper T cells required for autoantibody production and immune complex fonmation, either in the circulation, as in lupus (Woods & Zvaiflcr 1989), or directly on the target organ, as in anti-receptor autoimmune diseases such as myasthenia gravis (Lindstrom et al. 1988). Cell transfer experiments (Zamvil et al. 1985, Holmdahl et al. 1985, Bendelac et al. 1987, Miller et al. 1988) and the inhibitory effects of anti-CD4 antibodies (Wofsy & Seaman 1985, Koiki et al. 1987, Ranges et al. 1985) in experimental models of autoimmunity have been used to document these roles.

Thymic selection defines multiple T cell receptor V beta 'repertoire phenotypes' at the CD4/CD8 subset level.

We describe here the use of a sensitive and accurate multiprobe V beta RNase protection assay in characterizing the expression levels of 17 V beta genes in separated CD4+ and CD8+ subsets of selected mouse strains. The IE‐reactive V beta genes (V beta s 11, 12, 5.1 and 16) showed various patterns of skewed subset expression in different strains, suggesting additional influences of IA, class I, and non‐MHC genes in the selection process. Clonal deletion of V beta 11‐ and V beta 12‐bearing T cells, among others, was skewed strongly towards the CD4+ subset in many IE+ mouse strains, supporting the notion that negative selection can cause incomplete, subset biased, V beta clonal deletions. Broad analysis in separated CD4+ and CD8+ subsets gave improved resolution of V beta repertoire selection, and revealed significant strain and/or subset specific skewing for additional V beta genes; with consistent bias towards higher expression of V beta 7 and V beta 13 in the CD8+ subset, and V beta 15 in the CD4+ subset of most mouse strains. The influence of diverse non‐MHC ligands in V beta repertoire selection was further illustrated by the identification of unique V beta repertoires for six different MHC‐identical (H2k) strains. Such polymorphisms in TCR repertoire expression may help to define better disease susceptibility phenotypes.

Molecular aspects of murine systemic lupus erythematosus

Murine systemic lupus erythematosus (SLE) is a good model of human SLE since most of the immunologic abnormalities apparently fundamental to the human disease also appear to be operative in the mouse. Thus, it is felt that understanding the pathogenesis and etiology of murine lupus should lead to a better comprehension of this human diseases, and of autoimmunity and immunoregulation in general. New Zealand Black (NZB) mice and the F 1 hybrids produced by the mating of NZB with New Zealand White (NZW) mice [(NZBxW)F1] were the first described models of spontaneous lupus-like autoimmune disease [reviewed in 29]. Several decades of study of this disease in New Zealand (NZ) mice provided a reasonable understanding of its pathology and enumerated a variety of immunologic and virologic peculiarities, but contributed little knowledge about the etiologic mechanisms involved. The recent availability of two new strains of mice (MRL, BXSB) that also spontaneously develop a SLE-like syndrome [3, 45] has greatly enhanced the potential value of murine SLE as an experimental model since essential immunopathologic common denominators of the disease can now be identified. The various strains of mice which are predisposed to the development of lupus, their H-2 and Igh haplotype, lymphocyte surface alloantigens, accelerating factors, and survival rates are listed in Table 1, and their immunopathologic and serologic characteristics have been reviewed in detail elsewhere [62]. Perhaps the most significant feature is that no two have the same H-2 complex, nor the same Igh haplotype, suggesting that no single or simple genetic explanation of the

Novel origin of lpr and gld cells and possible implications in autoimmunity

The lpr and gld mutations are prime examples of single-gene defects associated with expansion of a unique double-negative (CD4-8-), T-cell receptor alpha:beta + cell population and heightened polyclonal and autoimmune responses. The exact origin of these autoimmunity-inducing/enhancing T cells remains controversial. Here, we review the characteristics of the lpr and gld mutations, and speculate on the possible relationship of these cells to normal thymic differentiation pathways. We argue that mounting evidence now supports the existence of a CD4/CD8-loss pathway of late thymic differentiation, responsible for the origin of both normal and lpr/gld double-negative alpha:beta + cells. We further speculate that downregulation of CD4 and CD8 accessory molecules on thymocytes with moderately autoreactive T-cell receptors is involved in selecting cells, including lpr/gld precursors for this pathway. Escape of a large number of such autoreactive cells from thymic elimination might be an important contributory factor to the pathogenesis of autoimmunity.

B and T cell antigen receptor repertoires in lupus/arthritis murine models

Autoimmune diseases affect a large segment of the population with diverse systemic or organ-specific manifestations, and include systemic lupus erythematosus (SLE), rheumatoid arthritis, a variety of endocrine disorders, myasthenia gravis, skin diseases and others [121]. The immune system participation in these diseases has been documented at the humoral or cellular level, or both. Studies in appropriate animal models [8, 122], especially those with spontaneous disease, have provided important insights into the immunopathological features of these diseases and the mechanisms leading to end-stage tissue damage. Nevertheless, although several theories have been proposed [121], very little is known about how an autoimmune response is initiated and maintained. In attempting to address this question, we and others have focused our efforts on the molecular genetics of antigen receptor genes, both at the genomic and expression levels. The products of these genes, together with the major histocompatibility complex (MHC) molecules, are intimately involved in antigen binding and presentation, the quantitative and qualitative aspects of the immune response, immunological network regulation and tolerance induction. It is, therefore, reasonable to suspect that abnormalities in the genomic or expressed repertoires of these genes might be involved in the induction of autoimmune diseases either directly or indirectly. Below, we summarize our findings in this area working primarily with murine models of lupus/arthritis.

Antigen Receptor Genes in Autoimmune B and T Cells

Abnormal humoral and/or cellular autoimmune responses of sufficient magnitude and duration are sometimes considered the primary, and at other times secondary, contributors to many human and animal diseases (l), Clinically, the wide spectrum of autoimmune diseases has been divided into two main categories: systemic and organ-specific diseases. Types of autoimmune diseases frequenty overlap, and more than one autoimmune disorder tends to occur in the same individual. Among the non-organ-specific diseases, systemic lupus erythematosus serves as the prototype.