Involvement of the peripheral benzodiazepine receptor in the development of cutaneous pathology in Mrl/Lpr mice

Mrl/Lpr mice develop inflammatory pathologies similar to human lupus erythematosus (LE). In that model, we showed a protective effect of different peripheral benzodiazepine receptor (PBR) ligands: PK 11195, Ro5-4864 and the newly described SSR180575 on the development of the cutaneous lesions. Specifically, we evidenced that a chronic treatment at 3 mg/kg per i.p. for 30 days prevented acanthosis, hyperkeratosis and generation of dermal infiltrates as compared with control untreated mice. In addition, using a specific polyclonal anti mouse PBR antibody, we characterized PBR expression in the skin lesions, and we observed that PBR expression in the epidermal component was increased when Mrl/Lpr mice developed the pathology and diminished upon PBR ligand treatment. PBR expression modulation together with the protective effects of its ligands further reinforce the role that PBR may play in the regulation of inflammation processes. Provided the exact mechanism of action that accounts for PBR action in that process is elucidated, these data support new therapeutic applications for specific potent PBR ligands.     

Genomic view of IFN-alpha response in pre-autoimmune NZB/W and MRL/lpr mice

Interferon (IFN)-alpha is involved in the pathogenesis of systemic lupus erythematosus. Studies in murine lupus models have revealed that type I IFN exerts either a protective effect in MRL/lpr, or can detrimentally impact disease progression, as in NZB/W mice. To understand this paradox, we examined the kinetic global gene expression in pre-autoimmune NZB/W-, MRL/lpr- and normal BALB/c-derived splenic mononuclear cells following ex vivo IFN-alpha treatment. Analysis of IFN-alpha-induced gene expression patterns revealed genes associated with antiproliferative activity of IFN-alpha including CDKN1A, GADD45B, pituitary tumor-transforming 1, SCOTIN, ataxia telangiectasia-mutated homolog and calcyclin-binding protein were upregulated in MRL/lpr and/or BALB/c mice. Of IFN-alpha-induced genes differentially expressed in NZB/W vs BALB/c and MRL/lpr mice at 3 h time point, enhanced expression of CCND1, cyclin D2, matrix metalloproteinase 13 and a panel of cytokines and chemokines and impaired expression of negative inflammatory regulators CD69 and an Src family kinase hemopoietic cell kinase were notable. Interestingly, the splenic mononuclear cells from the NZB/W not MRL/lpr lupus-prone mice at the pre-autoimmune stage before ex vivo IFN-alpha treatment, have increased expression of many known IFN-regulated genes. These results provide a unique genomic view of ex vivo IFN-alpha response in two lupus-prone models, and help to have an insight into the role of IFN-alpha in lupus pathogenesis.     

Inflammatory modulation of PPAR gamma expression and activity

Nitric oxide (NO) production increases with age in the lupus-prone MRL/lpr mouse, paralleling disease activity. One mechanism for excess NO production in MRL/lpr mice may be a defect in down-regulatory mechanisms of the iNOS pathway. A potential modulator of NO is the nuclear hormone receptor peroxisome proliferation activated receptor gamma (PPARgamma). We demonstrate that renal PPARgamma protein expression was altered as disease progressed in MRL/lpr mice, which paralleled increased iNOS protein expression. Additionally, MRL/lpr-derived primary mesangial cells expressed less PPARgamma than BALB/c mesangial cells and produced more NO in response to LPS and IFNgamma. Furthermore, PPARgamma activity was reduced in mesangial cells following exposure to inflammatory mediators. This activity was restored with the addition of a NOS enzyme inhibitor. These results indicate that the activation of inflammatory pathways may lead to reduced activity and expression of PPARgamma, further exacerbating the disease state.     

Aberrant expression of GM1 on lymph node cells of MRL/Mp-lpr/lpr mice: influences on the autoreactivities of anti-asialo GM1 antibodies.

Although changes in surface carbohydrate expression of abnormally expanded MRL/Mp-lpr/lpr (MRL/lpr) lymph node (LN) cells have previously been described, the composition and function of glycolipids present on these cells as well as the spectrum of specificity of anti-carbohydrate antibodies reactive with these cells remains obscure. Analysis of antibodies to a panel of 22 carbohydrate structures using a liposome immune lysis assay (LILA) showed that, except for anti-asialo GM2 (GA2) antibodies, marked reduction of antiglycolipid antibody levels was observed in sera from 4-mo-old MRL/lpr mice compared with these from MRL/Mp(-)+/+ (MRL/+) mice. Absorption experiments revealed that both anti-asialo GM1 (GA1) and globoside antibodies had binding capacity to MRL/lpr LN cells. To elucidate the glycolipid profiles of MRL/lpr LN cells, glycolipids were extracted from LN cells of both MRL/lpr and MRL/+ mice and analysed. A 30-fold elevation of GM1 was found in MRL/lpr LN cells compared with MRL/+ LN cells. From the results of LILA using GA1/GM1 mixed liposomes, aberrantly expressed GM1 inhibited the classical complement pathway but did not interfere with the binding of anti-GA1 antibodies to liposomal GA1. These findings suggest that a drastic GM1 increase on MRL/lpr LN cells would inhibit the action of anti-GA1 antibodies and complement on the cell surface. This may explain the escape of these cells from an activated self directed immune response.     

Absence of functional alternative complement pathway alleviates lupus cerebritis

The complement inhibitor, Crry, which blocks both the classical and alternative pathways, alleviates CNS disease in the lupus model, MRL/MpJ-Tnfrsf6lpr (MRL/lpr) mice. To understand the role of the alternative pathway, we studied mice deficient in a key alternative pathway protein, complement factor B (fB). Immune deposits (IgG and C3) were reduced in the brains of MRL/lpr fB-deficient (fB-/-MRL/lpr) compared to fB-sufficient (MRL/lpr) mice, indicating reduced complement activation. Reduced neutrophil infiltration (22% of MRL/lpr mice) and apoptosis (caspase-3 activity was reduced to 33% of MRL/lpr mice) in these mice indicates that the absence of the alternative pathway was neuroprotective. Furthermore, expression of phospho (p)-Akt (0.16+/-0.02 vs. 0.35+/-0.13, p<0.03) was increased, while expression of p-PTEN (0.40+/-0.06 vs. 0.11+/-0.07, p<0.05) was decreased in fB-/-MRL/lpr mice compared to their MRL/lpr counterparts. The expression of fibronectin, laminin and collagen IV was significantly decreased in fB-/-MRL/lpr mice compared to MRL/lpr mice, indicating that in the lupus setting, tissue integrity was maintained in the absence of the alternative pathway. Absence of fB reduced behavioral alterations in MRL/lpr mice. Our results suggest that in lupus, the alternative pathway may be the key mechanism through which complement activation occurs in brain, and therefore it might serve as a therapeutic target for lupus cerebritis.     

激活FXR抑制MRL/lpr狼疮小鼠肝损害的研究

 目的:观察法尼酯衍生物X受体（FXR）激活是否减轻MRL/lpr狼疮小鼠肝损害。方法:检测FXR在MRL/lpr狼疮小鼠及正常BALB/c小鼠肝脏的表达;观察BALB/c小鼠和鹅去氧胆酸（CDCA）激活FXR的MRL/lpr小鼠再以伴刀豆球蛋白A(ConA)诱导肝脏炎症反应后的肝脏酶学、炎症因子及病理学的变化。结果:FXR在MRL/lpr狼疮小鼠肝脏中低表达;ConA能在MRL/lpr小鼠诱导出较对照BALB/c小鼠更严重的肝损害;激活FXR减轻MRL/lpr狼疮小鼠ConA诱导的肝脏炎症损伤,并减少一系列炎症因子的释放。结论: CDCA激活FXR 后,能减轻狼疮小鼠肝脏损害。FXR可能是系统性红斑狼疮肝损害的一个保护性因素,激活FXR可能成为狼疮肝损害的一个治疗途径。     

Interleukin-1 Contributes to High Level IgG Production in the Murine MRL/Ipr Lupus Model

The autoimmune syndrome in MRL/lpr mice resembles human lupus, both in its serologic and immunopathologic characteristics. The contribution of IL-1 to high-level Ig production in the MRL/lpr model is poorly understood. We investigated the effect of treating B-cell-enriched, or, B plus T cell suspensions derived from either pre-disease or diseased lupus-prone MRL/lpr mice with IL-1ß or IL-1 receptor antagonist (IL-1Ra). Disparate patterns of IgG production by B cells and B plus T cells derived from diseased versus pre-diseased MRL/lpr mice was observed following treatment with IL-1ß. Remarkably, IL-1ß caused significant suppression in IgG production by B cells derived from diseased MRL/lpr mice as compared to B cells derived from pre-disease mice. In mix-and-match experiments with B plus T cells from pre-disease and diseased MRL/lpr mice, both T cell help and B cell hyperactivity, originating in diseased MRL/lpr mice were found to be important factors in high-level IgG production in diseased MRL/lpr mice. Furthermore, IL-1Ra treatment of B plus T cell co-cultures derived from diseased MRL/lpr mice was able to significantly suppress IgG production, whereas, IL-1Ra treatment of B plus T cell co-cultures derived from pre-disease MRL/lpr mice demonstrated virtually no suppression in IgG production. Collectively, these results indicate a potentially important but complex role for IL-1 in influencing high-level IgG production in MRL/lpr mice with established disease.     

The role of vascular smooth muscle cells in experimental autoimmune vasculitis. I. The initiation of delayed type hypersensitivity angiitis.

The destruction of vascular smooth muscle cells (VSMCs) in autoimmune arteritis is a poorly understood phenomenon. For evaluation of the cellular interactions that may contribute to vasculitis, the immunobiology of VSMCs and lymphocytes was explored in vitro. Primary VSMC cultures were established, and the interaction of these cells (from normal or autoimmune mice) with lymphocytes was then assessed. Specifically, splenocytes from MRL/lpr or C3H mice were cocultivated with MRL/lpr or C3H VSMCs. Massive mononuclear cell clusters from normal and autoimmune mice enveloped MRL/lpr VSMCs, which culminated in the detachment of MRL/lpr VSMCs from the culture plate. In contrast, the interaction of SPs from either normal or autoimmune mice did not encompass or destroy normal VSMCs. Further investigation indicated that MRL/lpr, but not C3H, VSMCs spontaneously expressed Ia and released Il-1 like factor(s), which may be at least two mechanisms by which MRL/lpr VSMCs stimulate the in vitro mononuclear cell influx. As a result of these studies, a novel mechanism for the induction of mononuclear cell autoimmune vasculitis is proposed. VSMCs derived from autoimmune mice may stimulate a mononuclear inflammatory cell phlogistic response which culminates in VSMC autodestruction.     

AID dysregulation in lupus-prone MRL/Fas(lpr/lpr) mice increases class switch DNA recombination and promotes interchromosomal c-Myc/IgH loci translocations: modulation by HoxC4

Immunoglobulin gene somatic hypermutation (SHM) and class switch DNA recombination (CSR) play important roles in the generation of autoantibodies in systemic lupus erythematosus. Systemic lupus is characterized by the production of an array of pathogenic high-affinity mutated and class-switched, mainly IgG, antibodies to a variety of self-antigens, including nuclear components, such as dsDNA, histones, and chromatin. We previously found that MRL/Fas(lpr/lpr) mice, which develop a systemic autoimmune syndrome sharing many features with human lupus, display greatly upregulated CSR, particularly to IgG2a, in B cells of the spleen, lymph nodes, and Peyer's patches. In MRL/Fas(lpr/lpr) mice, the significant upregulation of CSR is associated with increased expression of activation-induced cytidine deaminase (AID), which is critical for CSR and SHM. We also found that HoxC4 directly activates the promoter of the AID gene to induce AID expression, CSR and SHM. Here, we show that in both lupus patients and lupus-prone MRL/Fas(lpr/lpr) mice, the expression of HoxC4 and AID is significantly upregulated. To further analyze the role of HoxC4 in lupus, we generated HoxC4(-/-) MRL/Fas(lpr/lpr) mice. In these mice, HoxC4-deficiency resulted in reduced AID expression, impaired CSR, and decreased serum anti-dsDNA IgG, particularly IgG2a, autoantibodies, which were associated with a reduction in IgG deposition in kidney glomeruli. In addition, consistent with our previous findings in MRL/Fas(lpr/lpr) mice that upregulated AID expression is associated with extensive DNA lesions, comprising deletions and insertions in the IgH locus, we found that c-Myc to IgH (c-Myc/IgH) translocations occur frequently in B cells of MRL/Fas(lpr/lpr) mice. The frequency of such translocations was significantly reduced in HoxC4(-/-) MRL/Fas(lpr/lpr) mice. These findings suggest that in lupus B cells, upregulation of HoxC4 plays a major role in dysregulation of AID expression, thereby increasing CSR and autoantibody production and promoting c-Myc/IgH translocations.     

High expression of interleukin-1beta in the corneal epithelium of MRL/lpr mice is under the control of their genetic background

MRL/Mp mice bearing the Fas deletion mutant gene, lpr (MRL/lpr), spontaneously develop polyarthritis, sialoadenitis and dacryoadenitis, resembling rheumatoid arthritis (RA), and also corneal involvement such as keratopathy and scleritis, which is a major complication in RA patients. In this study, we found that the expression levels of IL-1beta and MMP-1 mRNAs in cornea were high in both MRL/lpr and MRL/Mp-+/+ strains of mice at an age younger than when they develop any inflammatory lesions. This was not true of other inbred strains, even those bearing the lpr gene, and also not of (NZB x NZW) F1 lupus mice. There was no significant difference in the expression of IL-1alpha and TGFbeta in cornea in these strains. Using crosses between MRL/lpr and C3H/HeJ-lpr/lpr (C3H/lpr) mice, at least the expression of IL-1beta was found to be under the control of the MRL genetic background, likely with a recessive mode of inheritance. Considering that IL-1beta in cornea was detected particularly in the epithelial layer, the high expression of IL-1beta in cornea is most likely involved in the genetic predisposition for corneal involvement and possibly also for arthritis in an MRL strain of mice.     

Prevention of B220+ T cell expansion and prolongation of lifespan induced by Lactobacillus casei in MRL/lpr mice.

We examined the therapeutic effect of heat-killed Lactobacillus casei (LC) on MRL/lpr mice. Ingestion of a diet containing 0.05% (w/w) LC from the weaning period prolonged the lifespan and tended to reduce the proportion of B220+ T cells in the spleen and mesenteric lymph nodes (MLN) of MRL/lpr mice. When LC was intraperitoneally injected once a week after the age of 8 weeks, I-A- macrophages accumulated in the spleen as well as the peritoneum and macrophage progenitors increased in the bone marrow. Moreover, the amount of IL-6 mRNA in peritoneal macrophages was reduced by LC injection. Splenocytes from LC-injected MRL/lpr mice exhibited lower proliferative responses to mitogens than those from control MRL/lpr mice and the increase in number of B220+ T cells in the spleen and MLN was prevented by LC injection. However, LC injection affected neither expression of interferon-gamma (IFN-gamma) and IL-4 mRNAs nor proliferative capacities of splenic T cells. Our findings demonstrate that LC injection accelerates macrophage recruitment and prevents the expansion of B220+ T cells without affecting the functions of T cells in MRL/lpr mice. These immunological modulations induced by LC may lead to prolongation of the lifespan of MRL/lpr mice.     

Follicular dendritic cell dysfunction and disorganization of lymphoid structures in MRL/lpr mice.

The follicular dendritic cell (FDC) in secondary lymphoid organs plays a key role in the function of the germinal center (GC) of the lymphoid follicle (LF) for regulation of the humoral immune response. MRL MpJ-lpr/lpr (MRL/lpr) mice, which have an abnormal humoral immune response, are a model for autoimmune disease. The present study was undertaken to investigate FDC dysfunction and LF disorganization in the spleen and lymph nodes of MRL/lpr mice. In 12-week-old MRL/lpr mice, antigen (Ag) trapping of FDC and half-life of trapped Ag on FDC was reduced. Although immunohistochemistry revealed well-developed FDC networks positive for complement receptors and having in vitro immune complex trapping in cryostat sections, Ag-trapping was not detected in 16-week-old MRL/lpr mice. Moreover a marked decrease in the number of GC and that of GC cell of residual GC in the MRL/lpr mice was observed by 12 weeks of age. Also reduced expression of intercellular adhesion molecule-1, FcgammaRII/III, and FDC-specific Ag (FDC-M1) on FDC was detected in 16-week-old MRL/lpr mice. The accumulation of double negative (CD4-CD8-) T cells, which is a characteristic feature of MRL/lpr mice, was observed around LF; however they did not infiltrate the LF and FDC network. In conclusion the loss of Ag-trapping on FDC and simultaneous disorganization of the lymphoid structure may be related closely to the immunologic abnormality observed in MRL/lpr mice.     

Expression of Heterozygous lpr Gene in MRL Mice

Recently we showed that not only homozygous MRL lpr/lpr mice but also heterozygous MRL +/lpr mice display defective antigen- and mitogen-driven T-cell responses as well as polyclonal B-cell activation compared with congeneic MRL +/+ mice. In this study we examined the impact of the heterozygous lpr gene on organ pathology in kidneys, joints, and salivary glands, as well as serum levels of immunoglobulins and autoantibodies in young and old MRL mice. Only 1 out of 17 heterozygous lpr-bearing MRL mice developed clinically overt renal disease with significant proteinuria and haematuria during the first year of life. However, examination of Ig and C3 deposits in glomeruli of kidneys from these mice revealed that the expression of the heterozygous lpr gene in MRL mice accelerates glomerulonephritis. In addition, histological examination of the submandibular salivary glands showed an increased focus score in heterozygous MRL mice at 4-5 months of age compared with that of matched congeneic +/+ mice. In contrast, no signs of arthropathy were registered in the heterozygous lpr-bearing MRL mice. Heterozygous MRL mice displayed an expanding lymphoid system as evaluated by significantly increased spleen and lymph node weights compared with those of matched MRL +/+ mice. Further evidence for immunomodulatory properties of the heterozygous lpr gene was obtained when analysing serum levels of IgG, IgM, and autoantibodies. Thus, heterozygous MRL +/lpr mice produced significantly higher levels of both Ig and autoantibodies than matched MRL +/+ mice. We conclude that the expression of the heterozygous lpr gene in MRL mice results in acceleration of the autoimmune process, giving rise to precocious clinical disease.     

The central and multiple roles of B cells in lupus pathogenesis

Summary: A standard view of B cells in systemic autoimmunity is that they promote lupus by producing autoantibodies (autoAb). However, this view is incomplete because recent studies have revealed that autoimmune disease can be dissociated from autoAb deposition. Furthermore, the spontaneous T-cell activation and organ infiltration in systemic lupus erythematosus patients and animal models are difficult to explain entirely via a direct autoAb-mediated mechanism. In this review, we describe work addressing the B-cell functions of autoantigen presentation and autoAb production in lupus pathogenesis. In the J_HD-MRL-Fas^lpr strain (JHD/lpr), a B-cell-deficient version of the lupus-prone MRL-Fas^lpr (MRL/lpr) mouse, spontaneous nephritis and dermatitis is abrogated, demonstrating that B cells have a primary role in disease. B cells play a similar role in Fas-intact, lupus-prone MRL mice. To address the role of autoantigen presentation, we analyzed transgenic mice which have B cells that cannot secrete immunoglobulin (mIgM transgenic mice). The restoration of B cells without antibody caused substantial interstitial nephritis and vasculitis although less marked than the intact MRL/lpr controls. To address the role of autoAb, we infused serum from aged MRL/lpr mice into J_HD/lpr mice. At most, mild to no nephritis was observed in the infused mice. These results indicate that B cells are promoting autoimmunity in mechanisms other than autoAb secretion, and we describe a model depicting these B-cell roles in the context of other inflammatory events in lupus.     

Intestinal intraepithelial lymphocyte T cells are resistant to lpr gene-induced T cell abnormalities.

The mucosal immune system of the gastrointestinal (GI) tract consists of Peyer's patches (PP), which are IgA inductive sites, and more diffuse effector regions which include cells in the intraepithelial lymphocyte (IEL) compartment. Since autoimmune MRL lpr/lpr (MRL/lpr) mice develop a proliferating CD3+, CD4-, CD8- (double negative; DN), B220+ T cell subset in systemic lymphoid tissue, we have initiated studies to determine the distribution of CD3+, DN, B220+ T cells (B220+ T cells or lpr/lpr T cells) in the GI immune system. Specifically, we examined T cell subsets separated according to expression of CD4, CD8, Thy-1, B220, alpha/beta T cell receptor (TcR) and gamma/delta TcR in PP and IEL of MRL/lpr mice at 6, 12 and 21 weeks of age. Increased numbers of CD3+ T cells were noted in both PP and spleen of 12- and 21-week-old mice in which the development of autoimmune disorders were also evident. However, normal numbers of CD3+ IEL T cells were seen in MRL/lpr mice in all three age groups tested. When the presence of T cell lymphadenopathy was examined in both IgA inductive and effector tissues, the PP followed the B220+ T cell pattern seen in the spleen, where approximately 30%-50% of CD3+ T cells in the PP of 12- and 21-week-old MRL/lpr mice expressed the phenotype of lpr/lpr T cells and greater than 90% were alpha/beta TcR+. On the other hand, B220+ T cells had not developed in PP or spleen of 6-week-old MRL/lpr mice. Of interest was the finding that IEL from lpr/lpr homozygous mice did not contain B220+ T cells in any age group tested. In this regard, the IEL of MRL/lpr mice comprised an identical pattern and frequency of CD4-/CD8+, CD4+/CD8-, DN and CD4+/CD8+ (double positive, DP) T cell subsets as their normal counterparts (i.e. MRL +/+, BALB/c and C3H/HeN mice) which consisted of approximately 75%, approximately 7.5%, approximately 7.5% and approximately 10%, respectively. Further, Thy-1, gamma/delta TcR and alpha/beta TcR expression in these four subsets of MRL/lpr IEL were very similar to normal mice. These results suggest that the intestinal IEL compartment is minimally affected by the lpr/lpr mutation which induces T cell abnormalities and indicate that B220+ T cells do not preferentially home to IEL. Further, our results support the concept that IEL T cells develop as a separate T cell lineage from thymus-derived cells.     

Defective DNA methylation and CD70 overexpression in CD4+ T cells in MRL/lpr lupus-prone mice

We have determined that abnormal DNA methylation in T cells coincides with the development of autoimmunity, using a mouse model that exhibits an age-dependent lupus-like disease (MRL/lpr mice). Splenic CD4(+) T cells were isolated from these mice at 5 and 16 wk of age (before and after autoimmunity is established) and the expression of DNA methyltransferase 1 (Dnmt1) and the methylation-sensitive gene Tnfsf7 (CD70) was measured. Bisulfite DNA sequencing was used to monitor the methylation status of the Tnfsf7 gene. We found that Dnmt1 steady-state mRNA levels were significantly lower in 16-wk-old MRL/lpr mice, which had established autoimmunity, compared to the 5-wk-old MRL/lpr mice. Furthermore, the expression of CD70 was higher in MRL/lpr mice at 16 wk. CD70 was overexpressed in MRL/lpr mice compared to age- and sex-matched MRL(+/+) controls. Bisulfite DNA sequencing of the Tnfsf7 gene in MRL/lpr mice revealed that at 16 wk, CG pairs were hypomethylated compared to 5-wk-old mice, and that Tnfsf7 from MRL/lpr mice was hypomethylated at 16 wk relative to age-matched MRL(+/+) controls. Our data indicate that decreased expression of Dnmt1 and the corresponding T cell DNA hypomethylation correlate with the development of age-dependent autoimmunity in MRL/lpr mice.     

Southern blot analysis of major histocompatibility genes of lpr mice

Several recent functional and immunofluorescent studies have suggested that abnormal major histocompatibility genes may be expressed in mice homozygous for the autoimmune disease-accelerating lpr (lymphoproliferation) gene. In an effort to establish the molecular basis of the expression of abnormal MHC molecules in these mice, we used MHC class I- and class II-specific cDNAs to probe endonuclease-digested genomic DNA from strains expressing lpr to look for restriction fragment length polymorphisms (RFLPs). The RFLP pattern of MRL/Mp-lpr/lpr (MRL/lpr) DNA, as determined using five restriction enzymes, was identical to that of MRL/MP-+/+ and typical of the H-2k haplotype exhibited by C3H/HeSnJ and AKR/J, which are the two H-2k haplotype strains from which MRL was derived. DNA from C57BL/6-lpr/lpr (B6/lpr) exhibited a pattern similar to C57BL/6, again indicating that the lpr gene did not alter MHC genes, within the limitations of this approach. Because macrophages derived from lpr mice had been specifically reported to express altered MHC haplotypes, DNA was prepared from MRL/lpr peritoneal macrophages and Southern blotting was performed using probes for I-A beta and I-E beta. The patterns observed were typical of H-2k DNA. The data thus indicate that the abnormalities of MHC genes previously observed in lpr mice may be due to the influence of other genes on MHC gene products, but are probably not due to alterations in MHC genes themselves.