Apoptosis and autoimmunity: complement deficiency and systemic lupus erythematosus revisited

New insights into complement: a mediator of injury and marker of disease activity in systemic lupus erythematosus

Studies performed during the past several decades have demonstrated a role for the complement system in both the etiology and pathogenesis of systemic lupus erythematosus (SLE). However the specifically defective molecular and cellular pathways responsible for the disease and its complications have generally not been identified. In this report, we describe two recent advances in complement pathobiology that highlight future directions for promising investigation toward enhancing our capacity to diagnose SLE, to monitor activity of the disease, and to identify molecular and cellular defects in SLE that can be targeted by therapeuticinhibitors of complement activation.In the first example, we describe recently developed assays to detect erythrocyte C4d and complement receptor1 for diagnosis and monitoring of disease activity in SLE. In the second example, we describe a recently discovered role for complement in mediating fetal loss in antiphospholipid syndrome and discuss the potential for this observation to facilitate identification and development of complement based biomarkers to predict poor fetal outcome in pregnant patients with SLE. These two examples are meant to underscore the importance of complement in the etiology and pathogenesis of SLE and its complications, and to stress the need for further investigation focused on the link between the complement system and SLE.

Association of FAS gene polymorphisms with systemic lupus erythematosus: A case-control study and meta-analysis

The association of functional polymorphisms in the promoter of the apoptosis gene FAS with systemic lupus erythematosus (SLE) susceptibility has been a controversial subject. We conducted a case-control study to investigate this association in a Chinese population and performed a meta-analysis in different populations. The single nucleotide polymorphisms (SNPs) rs2234767 (-1377G>A) and rs1800682 (-670A>G) were genotyped by TaqMan allelic discrimination assays in 552 Chinese SLE patients and 718 healthy controls. In our case-control study, we observed allelic association between the promoter SNP rs2234767 [P=0.033, odds ratio (OR)=0.836, 95% confidence interval (CI), 0.709-0.986] and SLE but not the SNP rs1800682. Haplotype analysis revealed that one haplotype of GA was significantly associated with the disease (P=0.039, OR=1.184, 95% CI, 1.009-1.391). In the meta-analysis available studies, including our data, were combined using the STATA software package v.7.0. The meta-analysis revealed a significant association between FAS polymorphisms and SLE (rs2234767 A vs. G allele; P=0.004, OR=0.819, 95% CI, 0.715-0.938, rs1800682 G vs. A allele: P=0.034, OR=0.791, 95% CI, 0.637-0.983). In conclusion, FAS gene polymorphisms may contribute to SLE susceptibility in the Chinese population, and the meta-analysis shows that FAS polymorphisms may be associated with SLE susceptibility in different populations.

Cell-Bound Complement Activation Products (CB-CAPs) as a Source of Lupus Biomarkers

Measurement of serum C3 and C4 has been used for several decades to monitor disease activity in patients with SLE. Despite the limited utility and recognized weaknesses of these assays, they have remained the gold standard during an era of unprecedented discovery in the complement field. The current urgent need for lupus biomarkers warrants efforts to mine the complement system for assays superior to serum C3 and C4. Recent studies of soluble and cell-bound complement activation products hold promise for achieving this goal.

Homozygous single nucleotide polymorphism of the complement C1QA gene is associated with decreased levels of C1q in patients with subacute cutaneous lupus erythematosus

We report an association between a non-familial form of photosensitive Lupus-specific skin disease, subacute cutaneous lupus erythematosus (SCLE), and a new single nucleotide polymorphism (SNP) in the C1QA gene. We also describe an association between this SNP and lower levels of serum C1q. This SNP consists of adenine replacing the third guanine in the codon for aminoacid residue Gly70 (position excludes the 22 amino acid leading peptide) that is located in the second exon of the C1QA gene. We have designated this SNP C1qA-Gly70GGA (the GenBank sequence at this location is C1qA-Gly70GGG). A survey of 19 SCLE patients showed that 11 (58%) were homozygous for C1qA-Gly70GGA SNP, seven (37%) were heterozygous, and only one patient (5%) was homozygous for the GenBank sequence. In contrast, only 13 of 62 (21%) normal controls were homozygous for the C1qA-Gly70GGA SNP, 41 (66%) controls were heterozygous and eight (13%) controls were homozygous for the GenBank sequence. Thus, the C1qA-Gly70GGA SNP is strongly associated with SCLE (P-value = 0.005 by chi-square analysis with Yates correction). This SNP would traditionally be classified as clinically silent as it does not encode a different amino acid. However, our studies have suggested that this SNP appears to be associated with a functional abnormality of C1q expression since its presence correlates inversely with serum levels of C1q antigenic protein in both SCLE patients and normal controls. The mechanism by which this phenotypic change is associated with the translationally silent (synonymous) ClqA-Gly70GGA genetic variation is currently unknown.

Malaria associated apoptosis is not significantly correlated with either parasitemia or the number of previous malaria attacks

The occurrence and intensity of lymphocyte apoptosis in blood samples from 79 outclinic patients with uncomplicated Plasmodium falciparum or Plasmodium vivax malaria and 30 healthy individuals were investigated. No difference in apoptosis percentages was detected between healthy individuals and malaria patients when ex vivo lymphocytes were analyzed. However, significantly increased apoptosis levels were observed in lymphocytes from both P. falciparum- and P. vivax-infected patients when the cells were cultured for 24 h. CD4(+)and CD8(+) T cells were affected to a comparable extent in P.falciparum- and P.vivax-infected patients. However, when we compared apoptosis values in infected and non-infected individuals it appeared that CD4(+) T cells were more susceptible than CD8(+) T cells. A significant increase in the sIL-2R plasma levels was observed in malaria patients when compared with healthy individuals and a positive correlation was observed between sIL-2R levels and apoptosis rates in infected patients presenting increased rates of apoptosis. An increased expression of Fas antigen was recorded after stimulation with P. falciparum antigen or anti-CD3 monoclonal antibody. These data show that a consistent proportion of the lymphocyte population dies by apoptosis during a malaria infection and that a period of time is necessary before in vivo activated cells can express the apoptotic process in vitro.

Neutralizing interferon alpha as a therapeutic approach to autoimmune diseases

Therapeutic antibodies directed against tumor necrosis factor alpha (TNF-alpha) for the treatment of rheumatoid arthritis, and against the human EGF receptor-2 (HER2) receptor for the treatment of breast cancer have provided significant clinical benefit for the patients. The success of these antibodies has also provided strong support for the possibility that increased activity of cytokines or growth factors is causally implicated in a variety of human diseases. Interferon alpha (IFN-alpha) is induced by viruses (linked by epidemiological studies to autoimmune diseases), has significant direct effects on both epithelial cells and the immune system, and then can be further induced by the autoantibodies and apoptotic cells generated by the actions of IFN-alpha. The direct and deleterious impact on target tissues, the ability to induce an autoimmune response, and the potential for a self-sustaining cycle of induction and damage suggests that IFN-alpha could be a pivotal factor in the development of autoimmune diseases. This review will evaluate the rationale for, possible approaches to, and safety concerns associated with, targeting interferon alpha (IFN-alpha) as a therapeutic strategy for the treatment of autoimmune diseases. While the approach may be applicable to several autoimmune diseases, there will be an emphasis on systemic lupus erythematosus and insulin dependent diabetes mellitus.

Association of autoantibodies to nuclear lamin B1 with thromboprotection in systemic lupus erythematosus: lack of evidence for a direct role of lamin B1 in apoptotic blebs

OBJECTIVE

To demonstrate the association between autoantibodies to nuclear lamin B1 (aLB1) and protection against thrombosis ("thromboprotection") in patients with systemic lupus erythematosus (SLE), and to elucidate the mechanism by which aLB1 cause thromboprotection in vivo. Since a number of autoantigens in SLE have been localized specifically to the external surface of apoptotic blebs, it was hypothesized that circulating aLB1 may block the procoagulant effect of apoptotic blebs by binding to LB1 displayed at the external bleb surface.

METHODS

A cross-sectional study was performed using serum samples obtained at first evaluation of 259 English Canadian and French Canadian patients from SLE registries at 3 hospitals. A case-control study was performed to analyze the relationship between aLB1 and lupus anticoagulant (LAC) status and thrombotic manifestations between onset of disease and last followup. Reactivity of aLB1 with Jurkat or endothelial cells, which had been induced to undergo apoptosis, was determined by indirect immunofluorescence. Localization of LB1 in apoptotic cells and blebs was analyzed by confocal microscopy and surface labeling of cell membrane proteins.

RESULTS

High-titer aLB1 was restricted to a subset of SLE patients (46 patients), with an overall frequency of 17.8% (range 11.6-24.3% in the 3 centers). LB1 antibodies were significantly associated with LAC but not with antibodies to cardiolipin (aCL) or beta(2)-glycoprotein I (anti-beta(2)GPI). The frequency of thrombosis differed markedly depending on aLB1 and LAC status, as follows: presence of LAC and absence of aLB1 50%, presence of both LAC and aLB1 22.7%, absence of both LAC and aLB1 25.5%, absence of LAC and presence of aLB1, 20.8%. Further subclassification of patients based on aCL and anti-beta(2)GPI status revealed that, in the presence of LAC but in the absence of aCL, anti-beta(2)GPI, and aLB1, the frequency of thrombosis was 40%, whereas in the presence of aLB1, it decreased strikingly, to 9.1%. LB1 was found to be translocated into surface membrane blebs during apoptosis and to be entirely enclosed within the apoptotic bleb plasma membrane of Jurkat and endothelial cells.

CONCLUSION

The presence of aLB1 in SLE patients with LAC essentially nullifies the strong prothrombotic risk associated with LAC. Hence, aLB1 is associated with thromboprotection. Reactivity of aLB1 with apoptotic blebs does not seem to play a direct role in mediating this protection, since LB1 is buried within apoptotic blebs and inaccessible to circulating aLB1. The mechanism by which aLB1 confers thromboprotection in SLE remains to be elucidated.

Navigating the maze of complement genetics: a guide for clinicians

Genetic deficiencies of nearly all of the 30 complement system proteins have been recognized clinically. In many instances, the molecular basis for the deficiency has been elucidated. As a byproduct of these studies, we now have new insights into the pathophysiologic role of complement studies in several acquired diseases. New targets for drug development are among the practical outcomes of work on complement genetics.

Apoptosis of skeletal muscle cells and the pathogenesis of myositis: a perspective

Apoptosis is a genetically controlled form of cell death that occurs in many biologic processes including embryogenesis, immune cell development, and maintenance of peripheral immune tolerance. Recent studies have yielded evidence suggesting that apoptosis of parenchymal cells may play a role in providing self-antigens to initiate autoimmune reactions. Skeletal muscle cells are fully differentiated and multinucleated. Apoptosis has been described in developing myoblasts and, recently, in mature myotubes. However, the involvement of apoptosis in skeletal muscle pathologies is unclear. This article reviews the available data concerning the occurrence of skeletal muscle cell apoptosis in selected muscle diseases. It also discusses the potential role of muscle cell apoptosis in the development of autoimmune diseases such as idiopathic inflammatory myopathies.

Apoptosis, clearance mechanisms, and the development of systemic lupus erythematosus

Cell death by apoptosis is an integral part of many biologic processes, including embryonic development, T- and B-cell selection, the elimination of potentially autoreactive lymphocytes in the periphery, and maintenance of lymphocyte homeostasis through activation-induced cell death. There is also increasing evidence that apoptosis may maintain immune tolerance and that it may be the process that generates the self antigens responsible for the initial development of autoimmunity. This review discusses some of the biochemical steps involved in the apoptotic process, how potentially immunogenic self antigens are generated during apoptosis, and the mechanisms by which the products of apoptosis are cleared and processed to avoid breaking immune tolerance.