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M J Walport

Publications and source records attributed to M J Walport.

At least 19 recordsLinked to original sources
PubMed2006

Identification of chromosome intervals from 129 and C57BL/6 mouse strains linked to the development of systemic lupus erythematosus.

Systemic lupus erythematosus is an autoimmune disease in which complex interactions between genes and environmental factors determine the disease phenotype. We have shown that genes from the non-autoimmune strains 129 and C57BL/6 (B6), commonly used for generating gene-targeted animals, can induce a lupus-like disease. Here, we conducted a genome-wide scan analysis of a cohort of (129 x B6)F2 C1q-deficient mice to identify loci outside the C1qa locus contributing to the autoimmune phenotype described in these mice. The results were then confirmed in a larger dataset obtained by combining the data from the C1q-deficient mice with data from previously reported wild-type mice. Both analyses showed that a 129-derived interval on distal chromosome 1 is strongly linked to autoantibody production. The B6 genome contributed to anti-nuclear autoantibody production with an interval on chromosome 3. Two regions were linked to glomerulonephritis: a 129 interval on proximal chromosome 7 and a B6 interval on chromosome 13. These findings demonstrate that interacting loci between 129 and B6 mice can cause the expression of an autoimmune phenotype in gene-targeted animals in the absence of any disrupted gene. They also indicate that some susceptibility genes can be inherited from the genome of non-autoimmune parental strains.

Animals↗
PubMed2006

Prevention of C5 activation ameliorates spontaneous and experimental glomerulonephritis in factor H-deficient mice.

Membranoproliferative glomerulonephritis (MPGN) type II (dense deposit disease) is an inflammatory renal disease characterized by electron-dense deposits and complement C3 on the glomerular basement membrane. There is no effective therapy. We investigated the role of C5 activation in a model of MPGN that develops spontaneously in complement factor H-deficient mice (Cfh(-/-)). At 12 months there was a significant reduction in mortality, glomerular cellularity, neutrophil numbers, and serum creatinine levels in Cfh(-/-) mice deficient in C5. Excessive glomerular neutrophil numbers, frequently seen in patients with MPGN during disease flares, were also observed in Cfh(-/-) mice after the administration of an antiglomerular basement membrane antibody. This exaggerated injurious phenotype was absent in Cfh(-/-) mice deficient in C5 but not in Cfh(-/-) mice deficient in C6, indicating a key role for C5 activation in the induction of renal lesions. Importantly, the renal injury was completely reversed in Cfh(-/-) mice pretreated with an anti-murine C5 antibody. These results demonstrate an important role for C5 in both spontaneous MPGN and experimentally induced nephritis in factor H-deficient mice and provide preliminary evidence that C5 inhibition therapy might be useful in human MPGN type II.

Animals↗
PubMed2006

Overlapping BXSB congenic intervals, in combination with microarray gene expression, reveal novel lupus candidate genes.

The BXSB mouse strain is an important model of glomerulonephritis observed in systemic lupus erythematosus (SLE). Linkage studies have successfully identified disease-susceptibility intervals; however, extracting the identity of the susceptibility gene(s) in such regions is the crucial next step. Congenic mouse strains present a defined genetic resource that is highly amenable to microarray analysis. We have performed microarray analysis using a series of chromosome 1 BXSB congenic mice with partially overlapping disease-susceptibility intervals. Simultaneous comparison of the four congenic lines allowed the identification of expression differences associated with both the initiation and progression of disease. Thus, we have identified a number of novel SLE disease gene candidates and have confirmed the identity of Ifi202 as a disease candidate in the BXSB strain. Sequencing of the promoter regions of Gas5 has revealed polymorphisms in the BXSB strain, which may account for the differential expression profile. Furthermore, the combination of the microarray results with the different phenotypes of these mice has allowed the identification of a number of expression differences that do not necessarily map to the congenic interval, but may be implicated in disease pathways.

Animals↗
PubMed2003

Antibody-mediated glomerulonephritis in mice: the role of endotoxin, complement and genetic background.

Antibody-mediated glomerulonephritis in man may be exacerbated by infection and this effect may be mediated by bacterial endotoxin. There is evidence supporting a role for endotoxin in heterologous nephrotoxic nephritis in rats, but the role of endotoxin in this model in mice has not previously been explored. Previous data in mice on the role of complement in this model are conflicting and this may be due to the mixed genetic background of mice used in these studies. We used the model of heterologous nephrotoxic nephritis in mice and explored the role of endotoxin, complement and genetic background. In this study we show a synergy between antibody and endotoxin in causing a neutrophil influx. We also show that C1q-deficient mice have an increased susceptibility to glomerular inflammation but this is seen only on a mixed 129/Sv x C57BL/6 genetic background. On a C57BL/6 background we did not find any differences in disease susceptibility when wildtype, C1q, factor B or factor B/C2 deficient mice were compared. We also demonstrate that C57BL/6 mice are more susceptible to glomerular inflammation than 129/Sv mice. These results show that endotoxin is required in this model in mice, and that complement does not play a major role in glomerular inflammation in C57BL/6 mice. C1q may play a protective role in mixed-strain 129/Sv x C57BL/6 mice, but the data may also be explained by systematic bias in background genes, as there is a large difference in disease susceptibility between C57BL/6 and 129/Sv mice.

Animals↗
PubMed2002

Murine glomerular mesangial cell uptake of apoptotic cells is inefficient and involves serum-mediated but complement-independent mechanisms.

An increased number of apoptotic bodies have been detected in glomeruli of non-nephritic kidneys of C1q-deficient mice. In these mice an in vivo impaired uptake of apoptotic cells by peritoneal macrophages was also demonstrated. Here we investigated whether C1q plays a role in the in vitro clearance of apoptotic cells by glomerular mesangial cells. Phagocytosis was assessed using a novel flow cytometric assay that was validated by immunofluorescence studies. The uptake of apoptotic cells by mesangial cells, measured as percentage of mesangial cells ingesting apoptotic cells, was approximately 25%, 10% and 10% for a T cell lymphoma line (RMA), thymocytes and neutrophils, respectively. The uptake reached a plateau phase after 3 h, was specific for apoptotic cells and was mediated by serum but not by complement components C1q or C3. The phagocytosis of apoptotic cells was significantly inhibited by Arg-Gly-Asp-Ser (RGDS), a peptide capable of blocking the interaction of thrombospondin with CD36 or the vitronectin receptor. Pretreatment of the mesangial cells with dexamethasone (200 nm) but not with LPS increased the uptake markedly. These findings indicate that murine mesangial cells are capable of taking up syngeneic apoptotic cells, although much less efficiently than professional phagocytic cells. They also show that serum proteins other than complement components mediate the removal of apoptotic cells by murine mesangial cells in vitro.

Animals↗
PubMed2001

Reconstitution of the complement function in C1q-deficient (C1qa-/-) mice with wild-type bone marrow cells.

Besides Ab-independent and Ab-dependent activation of the complement classical pathway in host defense, C1q plays a key role in the processing of immune complexes and in the clearance of apoptotic cells. In humans, C1q deficiency leads to systemic lupus erythematosus-like symptoms in over 90% of the cases, thus making this defect a strong disease susceptibility factor. Similarly, C1q-deficient mice (C1qa-/-) develop systemic lupus erythematosus-like symptoms, such as autoantibodies and glomerulonephritis. We have previously provided evidence that C1q is produced by cells of the monocyte-macrophage lineage. In this study, we have tested whether transplantation of bone marrow cells would be sufficient to reconstitute C1q levels in C1qa-/- mice. C1qa-/- mice received a single graft of 10(7) bone marrow cells from wild-type (wt) donors after irradiation doses of 6, 7, 8, or 9 Gy. Engraftment was monitored by a Y chromosome-specific PCR and a PCR that differentiated wt from C1qa-/- genotype. Serum levels of C1q Ag and C1 function increased rapidly in the recipient mice, and titers reached normal levels within 6 wk after bone marrow transplantation. In wt mice that received C1qa-/- bone marrow, serum levels of C1q decreased constantly over time and became C1q deficient within 55 wk. These data clearly demonstrate that bone marrow-derived cells are the source of serum C1q and are competent to reconstitute normal C1q serum levels in C1q-deficient mice. Therefore, stem cell transplantation could be a therapy for patients with hereditary C1q deficiency.

Animals↗
PubMed2001

Continual low-level activation of the classical complement pathway.

There is evidence that the classical complement pathway may be activated via a "C1-tickover" mechanism, analogous to the C3-tickover of the alternative pathway. We have quantitated and characterized this pathway of complement activation. Analysis of freshly collected mouse and human plasma revealed that spontaneous C3 activation rapidly occurred with the generation of C3 fragments in the plasma. By the use of complement- and Ig-deficient mice it was found that C1q, C4, C2, and plasma Ig were all required for this spontaneous C3 activation, with the alternative complement pathway further amplifying C3 fragment generation. Study of plasma from a human with C1q deficiency before and after therapeutic C1q infusion confirmed the existence of a similar pathway for complement activation in humans. Elevated levels of plasma C3 were detected in mice deficient in complement components required for activation of either the classical or alternative complement pathways, supporting the hypothesis that there is continuous complement activation and C3 consumption through both these pathways in vivo. Blood stasis was found to stimulate C3 activation by classical pathway tick-over. This antigen-independent mechanism for classical pathway activation may augment activation of the complement system at sites of inflammation and infarction.

Animals↗
PubMed2001

Autoantigen glycoprotein 70 expression is regulated by a single locus, which acts as a checkpoint for pathogenic anti-glycoprotein 70 autoantibody production and hence for the corresponding development of severe nephritis, in lupus-prone PXSB mice.

Retroviral envelope glycoprotein gp70 is present in the sera of immunologically normal and autoimmune-prone strains of mice. However, only lupus-prone mice spontaneously develop gp70-anti-gp70 immune complexes (gp70IC), and these have been implicated in the development of nephritis. We investigated the genetic factors that affect the production of both free serum gp70 and gp70IC in the lupus-prone BXSB mouse strain by analyzing (BXSB x (C57BL/10 x BXSB)F(1))- and (C57BL/10 x (C57BL/10 x BXSB)F(1))-backcrossed male mice. Production of gp70 mapped to a single major locus located on chromosome 13 (Bxs6) with a maximum log likelihood of the odds of 36.7 (p = 1.6 x 10(-38)). The level of gp70IC was highly dependent on Bxs6-related gp70 production, and high titer autoantibody production only occurred when serum gp70 levels were greater than a threshold value of approximately 4.0 microg/ml. The subdivision of the (BXSB x (C57BL/10 x BXSB)F(1))-backcrossed mice into those homozygous or heterozygous for Bxs6 enabled a remarkable association to be observed between high levels of gp70IC and severe nephritis in the Bxs6 homozygote population. A further mapping study in these two subgroups identified a previously unrecognized interval associated with the production of autoantibodies.

Animals↗
PubMed2001

Targeted deletion of the CD59 gene causes spontaneous intravascular hemolysis and hemoglobinuria.

The glycolipid-anchored glycoprotein CD59 inhibits assembly of the lytic membrane attack complex of complement by incorporation into the forming complex. Absence of CD59 and other glycolipid-anchored molecules on circulating cells in the human hemolytic disorder paroxysmal nocturnal hemoglobinuria is associated with intravascular hemolysis and thrombosis. To examine the role of CD59 in protecting host tissues in health and disease, CD59-deficient (CD59(-/-)) mice were produced by gene targeting in embryonic stem cells. Absence of CD59 was confirmed by staining cells and tissues with specific antibody. Despite the complete absence of CD59, mice were healthy and fertile. Erythrocytes in vitro displayed increased susceptibility to complement and were positive in an acidified serum lysis test. Despite this, CD59(-/-) mice were not anemic but had elevated reticulocyte counts, indicating accelerated erythrocyte turnover. Fresh plasma and urine from CD59(-/-) mice contained increased amounts of hemoglobin when compared with littermate controls, providing further evidence for spontaneous intravascular hemolysis. Intravascular hemolysis was increased following administration of cobra venom factor to trigger complement activation. CD59(-/-) mice will provide a tool for characterizing the importance of CD59 in protection of self tissues from membrane attack complex damage in health and during diseases in which complement is activated.

Animals↗
PubMed2001

Accelerated nephrotoxic nephritis is exacerbated in C1q-deficient mice.

C1q deficiency strongly predisposes to the development of systemic lupus erythematosus in humans and mice. We used the model of accelerated nephrotoxic nephritis in C1q-deficient mice to explore the mechanisms behind these associations. C1q-deficient mice developed severe glomerular thrombosis within 4 days of induction of disease, whereas wild-type mice developed mild injury. These findings suggest that C1q protects from immune-mediated glomerular injury. This exacerbated thrombosis was also seen in mice triply deficient in C1q, factor B, and C2, excluding a major pathogenic role for the alternative pathway of complement in this phenomenon. However, these mice did not develop elevated creatinine levels. No exacerbation of accelerated nephrotoxic nephritis was observed in mice doubly deficient in factor B and C2, suggesting a protective role for C1q against renal inflammation that is proximal to C2 activation. There were increased murine IgG deposits, neutrophil numbers, and apoptotic cells in the glomeruli of C1q-deficient mice compared with wild-type mice. Renal expression of genes encoding procoagulant proteins was also enhanced in C1q-deficient mice. The increased IgG deposits and apoptotic cells in the glomeruli of C1q-deficient mice suggest that the exacerbation of disease may be due to a defect in the clearance of immune complexes and/or apoptotic cells from their kidneys.

Animals↗
PubMed2001

Intact B cell tolerance in the absence of the first component of the classical complement pathway.

A critical role for complement in the regulation of self tolerance has been proposed to explain the strong association between complement deficiency and autoimmunity. To elucidate the role of the classical pathway of complement in the maintenance of B cell tolerance, C1q-deficient (C1qa-/-) mice were bred with anti-hen egg lysozyme (HEL) immunoglobulin (Ig(HEL)) and soluble HEL (sHEL) transgenic mice. B cell tolerance was intact in C1qa-/- mice. In vivo, double-transgenic (Ig(HEL)/sHEL) C1qa-/- and wild-type control mice down-regulated surface immunoglobulin expression on splenocytes and equivalent numbers of HEL-binding B cells accumulated in the periphery. Maturation of B cells, evidenced by CD21 expression, was retarded to the same extent and at a similar time point. The frequency of anti-HEL-producing plasma cells and serum levels of anti-HEL immunoglobulin were comparably reduced in control and C1qa-/- double-transgenic mice compared to control Ig(HEL) and C1qa-/- Ig(HEL) mice. Furthermore, splenocytes from double-transgenic C1qa-/- or wild-type mice did not modulate intracellular calcium levels after stimulation with HEL in vitro. These data demonstrate that a stable form of B cell anergy persists in the periphery of C1qa-/- mice, suggesting that activation of the classical pathway by C1q is not essential for the maintenance of B cell tolerance in this transgenic model.

Animals↗
PubMed2001

Temporary depletion of complement component C3 or genetic deficiency of C1q significantly delays onset of scrapie.

Following peripheral exposure to transmissible spongiform encephalopathies (TSEs), infectivity usually accumulates in lymphoid tissues before neuroinvasion. The host prion protein (PrPc) is critical for TSE agent replication and accumulates as an abnormal, detergent insoluble, relatively proteinase-resistant isoform (PrPSc) in diseased tissues. Early PrPSc accumulation takes place on follicular dendritic cells (FDCs) within germinal centers in lymphoid tissues of patients with variant Creutzfeldt-Jakob disease (vCJD), sheep with natural scrapie or rodents following experimental peripheral infection with scrapie. In mouse scrapie models, the absence of FDCs blocks scrapie replication and PrPSc accumulation in the spleen, and neuroinvasion is significantly impaired. The mechanisms by which the TSE agent initially localizes to lymphoid follicles and interacts with FDCs are unknown. Antigens are trapped and retained on the surface of FDCs through interactions between complement and cellular complement receptors. Here we show that in mice, both temporary depletion of complement component C3 or genetic deficiency of C1q significantly delays the onset of disease following peripheral infection, and reduces the early accumulation of PrPSc in the spleen. Thus, in the early stages of infection, C3 and perhaps C1q contribute to the localization of TSE infectivity in lymphoid tissue and may be therapeutic targets.

Animals↗
PubMed2001

Complement facilitates early prion pathogenesis.

New-variant Creutzfeldt-Jakob disease and scrapie are typically initiated by extracerebral exposure to the causative agent, and exhibit early prion replication in lymphoid organs. In mouse scrapie, depletion of B-lymphocytes prevents neuropathogenesis after intraperitoneal inoculation, probably due to impaired lymphotoxin-dependent maturation of follicular dendritic cells (FDCs), which are a major extracerebral prion reservoir. FDCs trap immune complexes with Fc-gamma receptors and C3d/C4b-opsonized antigens with CD21/CD35 complement receptors. We examined whether these mechanisms participate in peripheral prion pathogenesis. Depletion of circulating immunoglobulins or of individual Fc-gamma receptors had no effect on scrapie pathogenesis if B-cell maturation was unaffected. However, mice deficient in C3, C1q, Bf/C2, combinations thereof or complement receptors were partially or fully protected against spongiform encephalopathy upon intraperitoneal exposure to limiting amounts of prions. Splenic accumulation of prion infectivity and PrPSc was delayed, indicating that activation of specific complement components is involved in the initial trapping of prions in lymphoreticular organs early after infection.

Animals↗
PubMed2001

Ultraviolet-radiation-induced keratinocyte apoptosis in C1q-deficient mice.

Exposure to ultraviolet B radiation is an important trigger of both systemic and cutaneous disease flares in individuals with systemic lupus erythematosus. More than 90% of individuals with homozygous C1q deficiency develop a systemic-lupus-erythematosus-like illness, which is typically associated with a severe photosensitive rash. Apoptotic, human keratinocytes have been shown in vitro to bind C1q, in the absence of antibody. These observations, together with the hypothesis that a major source of the autoantigens driving the immune response in systemic lupus erythematosus comes from apoptotic cells, led us to investigate the effects of murine C1q deficiency on ultraviolet-radiation-induced keratinocyte apoptosis in vivo. In this work, we demonstrated C1q binding to apoptotic murine keratinocytes in vitro and showed for the first time that C1q is also present on sunburn cells in vivo. In addition to C1q, we detected C3 deposition on sunburn cells in both wild-type and C1q-deficient mice, suggesting activation of the alternative pathway. Following acute ultraviolet exposure in vivo, no difference in the rate of clearance of sunburn cells was found in C1q-deficient mice from three different genetic backgrounds, compared with strain-matched wild-type controls. Furthermore, chronic ultraviolet exposure did not result in the production of autoantibodies or the development of glomerulonephritis. Our findings suggest that C1q does not play a critical role in the physiologic clearance of apoptotic murine keratinocytes in vivo.

Acute Disease↗
PubMed2001

Immune complex processing in C1q-deficient mice.

Complement and Fcgamma receptors are known to mediate the processing of immune complexes (IC), and abnormalities in these mechanisms may predispose to the development of lupus. We explored the processing of IC in mice deficient in complement component C1q. 125I-labelled IC comprising Hepatitis B surface antigen (HBsAg)/human anti-HBsAg (HBsAg/Ab) were injected intravenously and the sites of IC clearance determined by direct counting of organ uptake at various time points. The liver and spleen were the main sites of IC uptake in all mice. The splenic uptake of IC was significantly reduced in the C1q-deficient mice compared with the control mice. C1q-deficient mice also exhibited an initial accelerated hepatic uptake of IC similar to that seen in human subjects with hypocomplementaemia. The hepatic localization of IC at later time points was similar in both groups of mice. These data in mice are consistent with previous observations in humans that confirm that the classical pathway of complement plays an important role in the appropriate processing of IC in vivo.

Animals↗