Kevin A. Davies

Immune complex processing in patients with systemic lupus erythematosus. In vivo imaging and clearance studies.

Abnormal processing of immune complexes (IC) may be important in the pathogenesis of systemic lupus erythematosus (SLE). The clearance of large soluble IC (comprising hepatitis B surface antigen (HBsAg)/anti-HBsAg) radiolabeled with 123I was examined in 12 normal subjects and 10 patients with SLE. IC localization was analyzed by static and dynamic gamma-scintigraphy. Initial IC clearance from blood was more rapid in patients (median t1/2 = 2.15 min) than normals (median t1/2 = 5.15 min) due to more rapid uptake in the liver. However, in the SLE group, up to 12% of complexes were released from the liver after 30-50 min. Splenic uptake of immune complexes was reduced in the patients and there was reduced ability to retain IC in this organ. Plasma complement levels and erythrocyte complement receptor type 1 numbers were reduced in the patients, resulting in defective opsonization of IC and reduced red cell binding in vivo. These observations support the hypothesis that IC handling is abnormal in SLE.

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.

Identification of intervals on chromosomes 1, 3, and 13 linked to the development of lupus in BXSB mice

OBJECTIVE To identify intervals containing systemic lupus erythematosus (SLE) susceptibility alleles in the BXSB strain of mice. METHODS We analyzed 286 (B10 x [B10 x BXSB]F1) backcross mice for a range of phenotypic traits associated with the development of SLE in BXSB mice. The mice were genotyped using 93 microsatellite markers, and the linkage of these markers to disease was studied by extreme-phenotype and quantitative trait locus analysis. RESULTS The disease phenotype in these backcross mice was less severe than that in BXSB mice. However, antinuclear antibody production was increased compared with the parental strain. We identified 4 areas of genetic linkage to disease on chromosome 1 (Bxs1-4), 1 on chromosome 3 (Bxs5), and another interval on chromosome 13 which were associated with various aspects of the phenotype. Bxs4 and Bxs5 are located in regions not previously linked to disease in other models of SLE. CONCLUSION SLE in the BXSB mouse model has a complex genetic basis and involves at least 5 distinct intervals located on chromosomes 1 and 3. There is evidence that different intervals affect particular aspects of the SLE phenotype.

Overrepresentation of the FCγ receptor type IIA R131/R131 genotype in caucasoid systemic lupus erythematosus patients with autoantibodies to C1q and glomerulonephritis

OBJECTIVE To test the hypothesis that there is an association between the Fcgamma receptor type IIA (FcgammaRIIA)-H/R131 polymorphism and autoantibodies to the collagenous region (CLR) of C1q in patients with systemic lupus erythematosus (SLE). METHODS One hundred ninety-five Caucasoid lupus patients were studied. Anti-C1q(CLR) antibodies in serum were measured by enzyme-linked immunosorbent assay (ELISA) and FcgammaRIIA genotype analysis was performed by polymerase chain reaction. Immunoglobulin subclass of the autoantibodies was measured by ELISA. RESULTS Fifty-six patients were anti-C1q antibody positive, and Ig subclass analysis indicated a predominance of IgG2 anti-C1q antibodies. Analysis of the SLE population as a whole revealed no significant difference in the allele frequencies of R131 and H131 compared with controls. There was, however, a significantly increased frequency of the R131 allele both in the anti-C1q-positive subgroup of patients (chi2 = 7.66, P<0.01) and in the 71 patients with nephritis (chi2 = 7.76, P< 0.01), compared with controls. CONCLUSION FcgammaRIIA-R131 constitutes a heritable susceptibility factor for the development of SLE with manifestations in the kidney in Caucasoid patients. The close associations demonstrated between this FcgammaRII variant, antibodies to C1q(CLR), and glomerulonephritis may be due to a failure of clearance of the potentially pathogenic IgG2 autoantibody.

The molecular basis of hereditary complement factor I deficiency

The molecular basis of hereditary complement factor I deficiency is described in two pedigrees. In one pedigree, there were two factor I-deficient siblings, one of whom was asymptomatic and the other suffered from recurrent pyogenic infections. Their factor I mRNA was analyzed by reverse transcription of fibroblast RNA followed by amplification using the polymerase chain reaction. Both siblings were homozygous for the same transversion (adenine to thymine) at nucleotide 1282 in the cDNA. This mutation causes histidine-400 to be replaced by leucine. The altered histidine is a semi-conserved residue within the serine proteinase family, although no function has been ascribed to it. The proband of the second pedigree studied was found to be a compound heterozygote. One allele had the same mutation as the first family, the second allele had a donor splice site mutation that resulted in the deletion of the mRNA encoded in the fifth exon (a low-density lipoprotein receptor domain) from its transcript.

Clinical significance of IgA anticardiolipin and anti-β2-GP1 antibodies in patients with systemic lupus erythematosus and primary antiphospholipid syndrome

The objectives of this study were to estimate the prevalence of IgA anticardiolipin antibodies (aCL) and anti-β2-glycoprotein 1 antibodies (aβ2-GPl) in a large number of patients with systemic lupus erythematosus (SLE) and primary antiphospholipid syndrome (PAPS) and to examine possible associations between the clinical manifestations of the APS and the levels of IgA aCL and aβ2-GPl. We also assessed the operative characteristics of IgA aCL and aβ2-GP1. We retrospectively studied 130 patients with SLE and 35 patients with PAPS. In all patients we measured IgG, IgM, and IgA aCL and aβ2-GP1 and recorded any of the clinical manifestations of the APS. IgA aCL were positive in 8.5% of patients with SLE and in 40% of patients with PAPS. Positive IgA aβ2-GP1 were found in 17.7% of patients with SLE and in 25.7% of patients with PAPS. IgA aCL were associated with a history of venous thrombosis, thrombocytopenia, and recurrent fetal loss. In contrast, we could not establish significant associations between IgA aβ2-GP1 and any of the clinical manifestations of the APS. Measurement of the IgA in addition to IgG and IgM aCL hardly changed the operative characteristics of aCL testing, while measurement of the IgA in addition to IgG and IgM aβ2-GP1 increased sensitivity but with a greater loss in specificity. IgA aCL is significantly associated with more than one of the clinical manifestations of the APS in contrast to the IgA aβ2-GP1. Routine measurement of the IgA isotype of both aCL and aβ2-GP1 does not improve the operative characteristics of aCL and aβ2-GP1 and therefore is not recommended at present.

Immune complex processing in C1q-deficient mice

Complement and Fcγ 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.

Both Fcγ Receptor I and Fcγ Receptor III Mediate Disease in Accelerated Nephrotoxic Nephritis

Recognition of immune complexes in glomeruli by activator Fcγ receptors (FcγRI and FcγRIII) is an important step in the development of glomerulonephritis. The low-affinity receptor (FcγRIII) has previously been shown to be important in passive heterologous immune complex glomerulonephritis. However, most forms of human glomerulonephritis involve an active immune response, and the relative importance of FcγRI (high-affinity receptor) and FcγRIII in an active model of glomerulonephritis is not known. We have now studied accelerated nephrotoxic nephritis in FcγRIII−/− mice and FcγRI/III double-deficient mice, and compared them with matched wild-type controls and FcRγ chain-deficient (FcRγ−/−) mice. Mice were immunized against sheep IgG and injected with sheep anti-mouse glomerular basement membrane antibody 5 days later. Both FcγRI/III double-deficient mice and FcRγ−/− mice were strongly protected from renal injury. In contrast, FcγRIII−/− mice developed substantial nephritis, although there was a dose-dependent partial protection from glomerular crescents and thrombosis. Despite this histological protection from injury, the macrophage infiltrate was not reduced, implying a dissociation of macrophage accumulation from activation in the absence of activatory FcγRIII. Therefore, both FcγRI and FcγRIII play a role in this active model of glomerulonephritis, because both had to be deficient to protect markedly from disease.

Both Fcγ and complement receptors mediate transfer of immune complexes from erythrocytes to human macrophages under physiological flow conditions in vitro

Abnormal clearance by the mononuclear phagocytic system of immune complexes (IC) is important in the pathogenesis of systemic lupus erythematosus (SLE). We have developed an in vitro model to investigate the cellular mechanisms involved in the transfer of soluble IC from erythrocytes to human macrophages under physiological flow conditions. In this assay, erythrocytes bearing fluorescently labelled IC are perfused over monolayers of human monocytes or monocyte‐derived macrophages in a parallel‐plate flow chamber, and transfer quantified using confocal microscopy and flow cytometry. Using aggregated human IgG as a model IC, we have been able to demonstrate transfer of IC from erythrocytes to macrophages. Blocking studies with specific neutralizing antibodies have shown that both complement and Fcγ receptors are required for IC transfer. Blockade of CR4 (αxβ2 integrin), FcγRIIa or FcγRIII reduced transfer, while anti‐CR3 (αmβ2 integrin) had no effect. Blockade of CR3, FcγRIIa or FcγRIII also reduced the number of adhesive interactions between fluorescently labelled IC‐bearing erythrocytes and macrophage monolayers. Taken together with the transfer data, this suggests differing roles for these receptors in the human IC transfer reaction that includes an adhesive function which facilitates IC processing by mononuclear phagocytes. Finally, a functional effect of the FcγRIIa R131/H131 polymorphism, important in susceptibility to SLE, has also been demonstrated using this model. Uptake of IgG2 but not IgG1‐containing soluble IC was reduced by macrophages from individuals homozygous for the R131 allelic variant of the receptor.

Randomized controlled trial of rituximab and cost-effectiveness analysis in treating fatigue and oral dryness in primary Sjogren's Syndrome

To investigate whether rituximab, an anti–B cell therapy, improves symptoms of fatigue and oral dryness in patients with primary Sjögrens syndrome (SS).