Reinhard Kofler

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.

Immunoglobulin kappa light chain variable region gene complex organization and immunoglobulin genes encoding anti-DNA autoantibodies in lupus mice.

We have investigated the genetic origin of autoantibody production in several strains of mice that spontaneously develop a systemic lupus erythematosus-like disease. Restriction fragment length polymorphism analyses of gene loci encoding kappa light chain variable regions (Igk-V) demonstrated, as shown previously for the Ig heavy chain locus, that autoantibody production and disease occur in different Igk-V haplotypes. Moreover, autoimmune mice with known genetic derivation inherited their Igk-V loci essentially unaltered from their nonautoimmune ancestors. New Zealand black lupus mice, with unknown genetic derivation, had a possibly recombinant Igk-V haplotype, composed of V kappa loci that were primarily indistinguishable from those of nonautoimmune strains from either of the two potential donor haplotypes. The heavy and light chain gene segments (variable, diversity, joining) encoding anti-DNA antibodies were diverse and often closely related, or even identical, to those found in antibodies to foreign antigens in normal mice. Only 1 of 11 sequenced variable region genes could not be assigned to existing variable region gene families; however, corresponding germline genes were present in the genome of normal mice as well. These data argue against abnormalities in the genes and mechanisms generating antibody diversity in lupus mice and suggest a remarkable genetic and structural diversity in the generation of anti-DNA binding sites.

The genetic origin of autoantibodies

Autoimmune disease appears to be a consequence of the generation of self-reactive antibodies. The relationship between these autoantibodies and antibodies directed against exogenous antigens has fostered much recent work, especially on the murine models of systemic lupus erythematosus and rheumatoid arthritis, as Reinhard Kofler and his colleagues review here. While the complexities surrounding the origin of self-specific antibodies are still to be completely unravelled, it appears that lupus autoantibody expression may not result from defects in lg germline genes nor in mechanisms generating antibody repertoires (variable region gene selection, rearrangement, somatic mutation) but follows the same general principles governing responses to foreign antigens.

Macrophage I-A/I-E expression and macrophage-stimulating lymphokines in murine lupus

Seeking common abnormalities in mice genetically predisposed to lupus-like autoimmune disease, we investigated (1) the ontogeny of Ia antigens (I-A/I-E) on the surfaces of resident peritoneal macrophages (rpM phi) of lupus and normal mice, (2) spontaneous and lectin-induced in vitro production of M phi-stimulating factors (interferon, IFN; M phi-activating factor, MAF; M phi-Ia-inducing/recruiting factor, MIRF), and (3) responses of rpM phi from such animals to Ia-inducing signals. Indirect immunofluorescence techniques showed that Ia+ rpM phi increased numerically during the life spans of MRL/Mp lpr/lpr, while no such increase was observed in age-matched non-lpr MRL/Mp +/+ or (MRL/Mp lpr/lpr X MRL/Mp +/+)F1 hybrid mice. However, neonatal thymectomy, which prevents lymphoproliferation and autoimmune disease in MRL/Mp lpr/lpr mice, had no effect on this enhanced M phi I-A/I-E expression. NZB mice developed a similar increase with age, whereas BXSB and (NZB X NZW)F1 lupus mice, like immunologically normal controls, had low numbers of I-A/I-E+ rpM phi. Cultured splenocytes of lupus mice, including those with high percentages of I-A/I-E+ rpM phi, did not spontaneously (in the absence of mitogens) elaborate MIRF, MAF, or IFN activity. Furthermore, concanavalin A-stimulated splenocytes from lupus mice, particularly strains with early autoimmune disease manifestations [MRL/Mp lpr/lpr, male BXSB, and female (NZB X NZW)F1] produced levels of these lymphokines that were lower than normal controls. MRL/Mp lpr/lpr and NZB rpM phi, when stimulated in vitro with the supernatant of a MIRF-producing T cell hybridoma, did not hyperrespond. Our study shows that increased I-A/I-E+ rpM phi occur in some, but not all, lupus mice and this increase does not correlate with increased spontaneous or mitogen-induced production of M phi-stimulating lymphokines nor with hyperresponsiveness to Ia-inducing signals.

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

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.