Pathogenesis of lupus dermatoses in autoimmune mice. IV. Association between cutaneous immunoglobulin deposition and anti-single-stranded DNA antibodies in sera

Animal models of cutaneous lupus erythematosus and lupus erythematosus photosensitivity

Over the past decade, the most exciting and important finding in SLE-prone mice is the discovery of Fas/Fas ligand systems in the pathogenesis of autoimmune phenomena. A human model for murine lpr/gld disease has also been reported recently. Furthermore, as shown in Table 2, studies on Ig variable region genes, TCR genes and MHC class II genes have given us much information concerning human and murine SLE. With respect to cytokines, IL-2 deficiency and the key role of IL-6 have been found in SLE-prone mouse strains, and Th2 cytokine production has been demonstrated to play a more pathogenic role than Th1 cytokine production in human and murine SLE except for MRL/pr mice. TGF is also very intriguing because TGF-beta knockout mice show SLE-like autoantibodies and Sjögren syndrome-like lymphoproliferation. Apart from these basic scientific investigations, there are also many promising and practical therapeutic approaches. In particular, treatments with anti-CD4 antibody and murine CTLA4Ig which bound B7 and blocked binding of CD28 to B7 are outstanding. However, it remains obscure whether such new approaches are effective for the skin lesions of SLE-prone mice, although some immunosuppressive agents such as FK506, cyclosporin and Chinese herbal medicines have been evaluated to determine their selective effects on the skin lesions of MRL/lpr mice. Needless to say, mouse models are not identical, but similar, to human diseases. However, they are important in the search for the underlying pathogenesis of autoimmune diseases on the basis of careful evaluation of the similarities and differences between human diseases and these models. If such studies are steadily performed, then inbred or experimental models will become more promising tools for the investigation of cutaneous lupus erythematosus.

Pathogenesis of lupus dermatoses in autoimmune mice. XIX. Attempts to induce subepidermal immunoglobulin deposition in MRL/Mp- +/+ mice

The deposition of immunoglobulin (Ig) at the dermo-epidermal junction (DEJ) of the skin, frequently observed in autoimmune mouse strains, is similar to that seen in patients with systemic lupus erythematosus (SLE). MRL/Mp-lpr/lpr (MRL/lpr) mice have an autosomal recessive mutant gene, lpr, which produces massive T-cell proliferation and accelerates the onset of autoimmune diseases. MRL/Mp- +/+ (MRL/n) mice lack the lpr gene, and do not develop autoimmune disease during the first year after birth under pathogen-free conditions. To verify the mechanisms of subepidermal Ig deposition in the skin of LE, we designed an experiment in which we could induce Ig deposition in the control MRL/n mice. Intraperitoneal injection of lymphoproliferative cells of aged MRL/lpr mice induced splenomegaly and splenic granulomatous angitis in the control MRL/n mice. Lipopolysaccharide (LPS), a polyclonal B-cell activator, induced slight splenomegaly and relatively high levels of serum Ig. Dermatopathological investigation revealed mild lymphocyte infiltration without positive Ig deposition at the DEJ of MRL/n mice treated with proliferative T cells. Injection of both proliferative T cells and LPS induced 50% positivity of subepidermal Ig deposition, and high levels of serum immunoglobulins and anti-double stranded DNA (anti-dsDNA) antibodies. These changes were not observed in MRL/n mice injected with thymocytes of newborn MRL/lpr mice. Skin lesions and lupus nephritis were not demonstrated in any of the mice tested. This study suggest that both the mild inflammatory reaction and the presence of anti-dsDNA antibodies are required for the induction Ig deposition at the DEJ in the skin of LE patients.

Histological detection of c-myb and c-myc proto-oncogene expression in infiltrating cells in cutaneous lupus erythematosus-like lesions of MRL/l mice by in situ hybridization

A relationship between lymphocytic activation and the overexpression of proto-oncogenes such as c-myb or c-myc has been demonstrated in human autoimmune disease. In autoimmune-prone MRL/l mice, which spontaneously develop lupus erythematosus (LE)-like lesions on the back, increased expression of myb RNA has been found in the lymphoid organs. We detected the overexpression of c-myb and c-myc proto-oncogenes in infiltrating cells in the cutaneous lesions of MRL/l mice by using in situ hybridization. No specific hybridization signals of either of the probes used were seen in the nonlesional skin of MRL/l mice or in the apparently normal skin of aged MRL/n and young MRL/l mice. These results suggest that the increased expression of myb and myc proto-oncogenes in the cutaneous LE-like lesions of MRL/l mice is related to a state of activation in the infiltrating cells and is involved in the development of these lesions.

Cross-reactivity of murine monoclonal anti-DNA antibodies with human and murine skin: a possible pathogenetic role in skin lesions of lupus erythematosus

Anti-DNA autoantibodies are known to cross-react with a wide variety of substances including cell-surface molecules. Thus, we examined cross-reactivities of 20 murine monoclonal anti-DNA antibodies with normal human and mouse skin tissues. Hybridomas producing these monoclonal antibodies were established from non-immunized spleen cells from autoimmune MRL-lpr/lpr mice, a strain characterized by spontaneous development of SLE-like disorders including skin changes. They were selected based on their reactivity to DNA in a typical enzyme-linked immunosorbent assay, in which nine monoclonal antibodies were reactive with both double-stranded DNA and single-stranded DNA, whereas nine monoclonals were reactive only with single-stranded DNA. Even though only seven of them were observed to stain nuclei, most of the monoclonal antibodies revealed strong and distinct cross-reactivities to various components of the skin tissues including the epidermal basement membrane, keratinocytes at different locations of the epidermis, melanocytes, Langerhans cells, Thy-1+ dendritic cells in the case of murine skin, and mast cells. Our results suggest a possible role of so-called anti-DNA antibodies with high or low affinities to DNA in the pathogenesis of cutaneous lesions of lupus erythematosus.

Susceptible cytotoxicity to ultraviolet B light in fibroblasts and keratinocytes cultured from autoimmune-prone MRL/Mp-lpr/lpr mice

The MRL/Mp-lpr/lpr (MRL/l) mouse is an autoimmune model of spontaneous lupus erythematosus (LE), in addition to lupus nephritis. In order to better understand the mechanisms of photosensitivity in LE, in vitro photocytotoxicity was examined by using fibroblasts and keratinocytes cultured from MRL/l mice, control MRL/Mp- +/+ (MRL/n) mice, and normal BALB/c mice. A colorimetric 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide assay and the acridine orange/ethidium bromide assay were used for determination of cytotoxicity. Fibroblasts cultured from newborn MRL/l mice showed higher susceptibility to single ultraviolet light B (UVB) light irradiation at a dose of 100-500 mJ than those from MRL/n, F1 hybrid of (MRL/l x MRL/n mice), and BALB/c mice. However, the susceptibility to UVB was not observed in young (1-month-old) and adult (4-month-old) MRL/l mice. UVA light irradiation was not cytotoxic. Keratinocytes cultured from MRL mice showed lower cytotoxicity to UVB irradiation than fibroblasts cultured. However, keratinocytes from newborn MRL/l mice showed higher cytotoxicity to 50 mJ UVB irradiation than cells from MRL/n mice. Syngeneic or allogeneic sera augmented UVB-induced cytotoxicity of fibroblasts cultured. UVB irradiation of spleen cells induced no significant difference of cytotoxicity between MRL/l and MRL/n mice. Based on the results of F1 hybrid of (MRL/l x MRL/n) mice, the susceptibility seemed to be associated with autoimmune traits and to be regulated by genetical background.

Phenotypes of immunocompetent cells and Ia antigen expression in oral mucosa and skin of autoimmune mouse strains

The phenotypic characteristics of resident and infiltrating cells in skin and oral mucosa of MRL/Mp-lpr/lpr (MRL-lpr), MRL/Mp+/+ (MRL-(+)), NZB x NZW F1 (NZB/W) and Balb/c mice have been studied using monoclonal antibodies (Mabs) and immunoperoxidase staining with the Avidin-Biotin Complex method. Macroscopically evident skin lesions appeared spontaneously exclusively in aging MRL-lpr mice. Infiltration of lymphocytes was detected within the mucosa and the skin of MRL-lpr-mice. These lymphocytes expressed predominantly L3T4 and to a lesser extent Lyt-2 phenotype (T helper/inducer and T suppressor/cytotoxic subset, respectively). Class II major histocompatibility complex antigen (Ia) expression was detected on macrophages, dendritic cells and few lymphoid cells in normal oral mucosa and skin of all strains examined. However, in the oral mucosa and skin lesions of the 4 months old MRL-lpr mouse also keratinocytes expressed Ia antigens. Keratinocytic Ia expression was also detected in oral mucosa of 8 months old MRL-(+) mice. The described immunopathological findings in skin and oral mucosa of old MRL-lpr mice show a number of important similarities to human SLE disease.

Effects of ultraviolet light irradiation on the skin of MRL/l mice

MRL/Mp-lpr/lpr (MRL/l) and MRL/Mp-+/+ mice were irradiated with middle-wavelength ultraviolet light (UVB), and the development of skin lesions, skin lupus band test (LBT), anti-DNA antibodies in sera, and the extent of glomerulonephritis of the kidney were examined. Long-term exposure to low doses of UVB irradiation accelerated the development of skin lesions and enhanced the intensity of the positive skin lupus band in MRL/l mice. The contents of anti-DNA antibodies in sera, the incidence of positive findings in LBT, and the extent of glomerulonephritis were not influenced by the UVB irradiation. The promotion of the development of the skin lesions in MRL/l mice by the UVB exposure was not considered to be associated with acceleration of systemic autoimmune phenomena.

Ultrastructural lupus band test in the skin of MRL mice

The ultrastructural localization of immunoglobulin deposits in the dermoepidermal junction of MRL/l mice was examined using immunoperoxidase staining. All specimens that showed positive findings at the basement membrane zone of the skin on light microscopy had reaction products at the sub-basal laminar area when observed by electron microscopy. In the skin that had no distinct eruptions or which was distant from the lesions, the reaction products were distributed mostly just beneath the basal lamina in fine to course granular deposits. In the lesional skin, they formed a rather uniformly granular pattern among the irregularly arranged collagen fibrils and increased fine fibrillar amorphous material under the highly infolded basal lamina. Some of the reaction products were located just on the collagen fibrils and some appeared to be related to the free basal lamina. From the perspective of immunoelectron microscopy, the skin eruptions of MRL/l mice may serve as a good dermatological model of human systemic lupus erythematosus.

Histamine metabolism in skin of MRL/l mice

Of several murine autoimmune models, MRL/Mp-lpr/lpr (MRL/l) mice are the most attractive from a dermatopathological point of view, because their skin lesions resemble the erythematous lesions of systemic lupus erythematosus (SLE). In order to clarify the pathogenesis of lupus dermatoses, histamine and its metabolizing activities in the skin of MRL/l mice were investigated. The specific activities of histamine-N-methyltransferase (HMT) in the skin of MRL/l mice were significantly lower than those in the skin of control mice i.e., MRL/Mp-+/+ (MRL/n), C57BL/6J, and BALB/c mice. In the dorsal lesional skin of MRL/l mice, HMT activities were markedly lower than those in normal abdominal skin. In addition, age-related analysis of HMT levels in the dorsal skin of MRL/l mice revealed that HMT activities reached their maximum at the age of 2 or 3 months and then decreased at 4 or 5 months when skin manifestation appeared: however, HMT activities in the abdominal skin increased almost linearly with age. There were no significant differences in histamine content in these mice, and diamine-oxidase activities were not detected in any skin specimens. From these results, it is suggested that impaired histamine metabolism is a particular biochemical feature of the skin of MRL/l mice.