The role of apoptosis proteins and complement components in the etiopathogenesis of systemic lupus erythematosus

Systemic lupus erythematosus is a prototypical autoimmune disease characterized by the deregulation of T and B cells, tissue infiltration by mononuclear cells, tissue damage and the production of autoantibodies. There is a consensus that accelerated apoptosis of circulating lymphocytes and/or impaired clearance of apoptotic bodies may increase the amount of nuclear antigens presented to T lymphocytes. This process is accompanied by autoimmune responses that can lead to the development of lupus. The dysfunction of apoptosis may be a direct consequence of alterations in proteins/genes such as Fas, Bcl-2 and C1q. Increased expression of Fas antigen could intensify the exposure of hidden antigens. The overexpression of Bcl-2 protein might inhibit the removal of auto-reactive cells, and the lack of C1q could impair the clearance of self-antigens. The complete knowledge of the role of apoptosis components in the etiopathogenesis of lupus could lead to the development of new therapies targeting the apoptotic threshold, which could result in a more specific and effective disease response compared to global immunosuppression. This review summarizes the role of each component of the apoptotic process in the pathogenesis of lupus.

Anti C1q antibodies in cutaneous lupus erythematosus

Autoantibodies against C1q are strongly linked to immune-complex disorders like systemic lupus erythematosus (SLE). Although anti-C1q antibodies have received much interest in the recent years, their biological functions remain unclear. Anti-C1q antibodies are strongly associated with lupus nephritis. Recent studies describe apoptosis as a key player in LE pathogenesis and C1q is an important opsonin, playing a central role in the uptake of apoptotic blebs. The aim of this study was to evaluate serum anti C1q antibodies, C1q with circulating immune complexes and correlation between serology and cutaneous apoptosis in patients with cutaneous lupus erythematosus.

MATERIAL AND METHODS

79 subjects were recruited and divided into 4 groups-13 healthy controls, 26 with discoid chronic lupus (DLE), 23 with systemic lupus erythematosus (SLE) and 17 with subacute lupus erythematosus (SCLE). Blood samples and skin punched-biopsy specimens were performed. Serum anti-C1q antibodies and C1q associated to the immune complexes concentrations were determined by ELISA. Cutaneous caspase-3 expression was evaluated by immunohistochemistry.

RESULTS

SLE and SCLE patients had significantly higher levels of anti-C1q antibodies and serum C1q-CIC levels when compared to healthy controls (p < 0.05). Serum anti-C1q antibodies correlated with proteinuria in SLE patients (p < 0.05). Anti C1q antibodies levels also correlated with cutaneous caspase 3 expression in SLE and SCLE patients (both p < 0.05).

CONCLUSIONS

Anti C1q antibodies might play a pathogenic role in SCLE pathogenesis and being positively associated with cutaneous apoptosis markers might be associated with a negative prognosis and secondary SLE development.

C1q nephropathy in a child presenting with recurrent gross hematuria

C1q nephropathy is a rare glomerular disease characterized by mesangial immune deposits with dominant or codominant staining for C1q. The exact pathogenesis leading to the mesangial immune deposits of C1q remains unknown. C1q nephropathy often presents with proteinuria in the nephrotic range, with an unpredictable or poor response to corticosteroid therapy. It is seen more commonly in older children and young adults and is more common in African Americans compared with Caucasians. We present a 4-year-old African American girl who presented with recurrent gross hematuria in the absence of proteinuria or hypertension and whose renal biopsy demonstrated dominant mesangial deposits of C1q. We conclude that C1q nephropathy should be considered in patients who present with recurrent gross hematuria.

Homozygosity for a novel mutation in the C1q C chain gene in a Turkish family with hereditary C1q deficiency

Hereditary complete deficiency of complement component C1q is associated with a high prevalence of systemic lupus erythematosus and increased susceptibility to severe recurrent infections. An 11-year-old girl was screened for immunodeficiency due to a history of recurrent meningitis and pneumonia. Immunologic studies revealed absence of classic pathway hemolytic activity and undetectable levels of Clq. Exon-specific amplification of genomic DNA by polymerase chain reaction followed by direct sequence analysis revealed a novel homozygous missense mutation at codon 48 in the C1q C gene causing a glycine-to-arginine substitution affecting the collagen-like region of C1q. No changes were seen in the exons of the A and B chains. The mutation affected both the formation and the secretion of C1q variant molecules. We describe a novel mutation in the C1q C chain gene that leads to an interchange in amino acids resulting in absence of C1q in serum.

Complement protein C1q reduces the stoichiometric threshold for antibody-mediated neutralization of West Nile virus

Virus neutralization is governed by the number of antibodies that bind a virion during the cellular entry process. Cellular and serum factors that interact with antibodies have the potential to modulate neutralization potency. Although the addition of serum complement can increase the neutralizing activity of antiviral antibodies in vitro, the mechanism and significance of this augmented potency in vivo remain uncertain. Herein, we show that the complement component C1q increases the potency of antibodies against West Nile virus by modulating the stoichiometric requirements for neutralization. The addition of C1q does not result in virolysis but instead reduces the number of antibodies that must bind the virion to neutralize infectivity. For IgG subclasses that bind C1q avidly, this reduced stoichiometric threshold falls below the minimal number of antibodies required for antibody-dependent enhancement (ADE) of infection of cells expressing Fc-gamma receptors (CD32) and explains how C1q restricts the ADE of flavivirus infection.

Heavily isotype-dependent protective activities of human antibodies against vaccinia virus extracellular virion antigen B5

Antibodies against the extracellular virion (EV or EEV) form of vaccinia virus are an important component of protective immunity in animal models and likely contribute to the protection of immunized humans against poxviruses. Using fully human monoclonal antibodies (MAbs), we now have shown that the protective attributes of the human anti-B5 antibody response to the smallpox vaccine (vaccinia virus) are heavily dependent on effector functions. By switching Fc domains of a single MAb, we have definitively shown that neutralization in vitro--and protection in vivo in a mouse model--by the human anti-B5 immunoglobulin G MAbs is isotype dependent, thereby demonstrating that efficient protection by these antibodies is not simply dependent on binding an appropriate vaccinia virion antigen with high affinity but in fact requires antibody effector function. The complement components C3 and C1q, but not C5, were required for neutralization. We also have demonstrated that human MAbs against B5 can potently direct complement-dependent cytotoxicity of vaccinia virus-infected cells. Each of these results was then extended to the polyclonal human antibody response to the smallpox vaccine. A model is proposed to explain the mechanism of EV neutralization. Altogether these findings enhance our understanding of the central protective activities of smallpox vaccine-elicited antibodies in immunized humans.

Synergy between ficolin-2 and pentraxin 3 boosts innate immune recognition and complement deposition

The long pentraxin 3 (PTX3) is a multifunctional soluble pattern recognition molecule that is crucial in innate immune protection against opportunistic fungal pathogens such as Aspergillus fumigatus. The mechanisms that mediate downstream effects of PTX3 are largely unknown. However, PTX3 interacts with C1q from the classical pathway of the complement. The ficolins are recognition molecules of the lectin complement pathway sharing structural and functional characteristics with C1q. Thus, we investigated whether the ficolins (Ficolin-1, -2, and -3) interact with PTX3 and whether the complexes are able to modulate complement activation on A. fumigatus. Ficolin-2 could be affinity-isolated from human plasma on immobilized PTX3. In binding studies, Ficolin-1 and particularly Ficolin-2 interacted with PTX3 in a calcium-independent manner. Ficolin-2, but not Ficolin-1 and Ficolin-3, bound A. fumigatus directly, but this binding was enhanced by PTX3 and vice versa. Ficolin-2-dependent complement deposition on the surface of A. fumigatus was enhanced by PTX3. A polymorphism in the FCN2 gene causing a T236M amino acid change in the fibrinogen-like binding domain of Ficolin-2, which affects the binding to GlcNAc, reduced Ficolin-2 binding to PTX3 and A. fumigatus significantly. These results demonstrate that PTX3 and Ficolin-2 may recruit each other on pathogens. The effect was alleviated by a common amino acid change in the fibrinogen-like domain of Ficolin-2. Thus, components of the humoral innate immune system, which activate different complement pathways, cooperate and amplify microbial recognition and effector functions.

Multiple routes of complement activation by Mycobacterium bovis BCG

Mycobacterium tuberculosis is the leading cause of infectious disease in humans in the world. It evades the host immune system by being phagocytosed by macrophages and residing intracellularly. Complement-dependent opsonisation of extracellular mycobacteria may assist them to enter macrophages. This work examines in detail the mechanisms of complement activation by whole mycobacteria using Mycobacterium bovis BCG as a model organism. M. bovis BCG directly activates the classical, lectin and alternative pathways, resulting in fixation of C3b onto macromolecules of the mycobacterial surface. Investigation into the classical pathway has shown direct binding of human C1q to whole mycobacteria in the absence of antibodies. Most human sera contain IgG and IgM-anti-(M. bovis BCG), and pre-incubation with human immunoglobulin enhances C1q binding to the bacteria. Therefore classical pathway activation is both antibody-independent and dependent. The bacteria also activate the alternative pathway in an antibody-independent manner, but Factor H also binds, suggesting some regulation of amplification by this pathway. For the lectin pathway we have demonstrated direct binding of both MBL and L-ficolin from human serum to whole mycobacteria and subsequent MASP2 activation. H-ficolin binding was not observed. No M. bovis BCG cell surface or secreted protease appears likely to influence complement activation. Together, these data provide a more detailed analysis of the mechanisms by which M. bovis BCG interacts with the complement system.

The design and characterization of oligospecific antibodies for simultaneous targeting of multiple disease mediators

Monoclonal antibodies are traditionally used to block the function of a specific target in a given disease. However, some diseases are the consequence of multiple components or pathways and not the result of a single mediator; thus, blocking at a single point may not optimally control disease. Antibodies that simultaneously block the functions of two or more disease-associated targets are now being developed. Herein, we describe the design, expression, and characterization of several oligospecific antibody formats that are capable of binding simultaneously to two or three different antigens. These constructs were generated by genetically linking single-chain Fv fragments to the N-terminus of the antibody heavy and light chains and to the C-terminus of the antibody C(H)3 domain. The oligospecific antibodies were expressed in mammalian cells, purified to homogeneity, and characterized for binding to antigens, Fcgamma receptors, FcRn, and C1q. In addition, the oligospecific antibodies were assayed for effector function, protease susceptibility, thermal stability, and size distribution. We demonstrate that these oligospecific antibody formats maintain high expression level, thermostability, and protease resistance. The in vivo half-life, antibody-dependent cellular cytotoxicity function, and binding ability to Fcgamma receptors and C1q of the test oligospecific antibodies remain similar to the corresponding properties of their parental IgG antibodies. The excellent expression, biophysical stability, and potential manufacturing feasibility of these multispecific antibody formats suggest that they will provide a scaffold template for the construction of similar molecules to target multiple antigens in complex diseases.

Immunoglobulin M is required for protection against atherosclerosis in low-density lipoprotein receptor-deficient mice

BACKGROUND

Immunoglobulin M (IgM) natural antibodies bind oxidatively-modified low-density lipoprotein (LDL) and apoptotic cells and have been implicated as being important for protection against atherosclerosis. We have directly investigated the requirement for IgM by studying the effects of IgM deficiency in LDL receptor-deficient (Ldlr(-/-)) mice.

METHODS AND RESULTS

Mice deficient in serum IgM (sIgM) or complement C1q were crossed with Ldlr(-/-) mice and studied on both low-fat and high-fat semisynthetic diets. On both diets, en face and aortic root atherosclerotic lesions in sIgM.Ldlr(-/-) mice were substantially larger and more complex, with accelerated cholesterol crystal formation and increased smooth muscle cell content in aortic root lesions. Combined C1q and IgM deficiency had the same effect as IgM deficiency alone. Increased apoptosis was observed in aortic root lesions of both sIgM.Ldlr(-/-) and C1qa.Ldlr(-/-) mice. Because lesions were significantly larger in IgM-deficient mice than in the absence of C1q, IgM protective mechanisms appear to be partially independent of classical pathway activation and apoptotic cell clearance. Levels of IgG antibodies against copper-oxidized LDL were lower in sIgM.Ldlr(-/-) mice fed a high-fat diet, suggesting compensatory consumption of IgG in the absence of IgM.

CONCLUSIONS

This study provides direct evidence that IgM antibodies play a central role in protection against atherosclerosis. The mechanism appears to be at least partly independent of classical pathway complement activation by C1q.

[Structure and function of complement protein C1q and its role in the development of autoimmune diseases]

Complement plays an important role in the immune system. Three different pathways of complement activation are known: the classical, alternative, and lectin dependent. They involve more than 30 serum peptides. C1q is the fi rst subcomponent of the classical pathway of complement activation.It is composed of three types of chains, A, B, and C, which form a molecule containing 18 peptides. Each of the chains has a short amino-terminal region followed by a collagen-like region(playing a role in the activation of C1r2C1s2) and a carboxy-terminal head, which binds to immune complexes. Recent studies have shown a great number of ligands for C1q, including aggregated IgG, IgM, human T-cell lymphotropic virus-I (HTLV-I), gp21 peptide, human immunodeficiency virus-1 (HIV-1) gp21 peptide, beta-amyloid, fragments of bacterial walls, apoptotic cells, and many others. However, the role of C1q is not only associated with complement activation.It also helps in the removal of immune complexes and necrotic cells, stimulates the production of some cytokines, and modulates the function of lymphocytes. Complete C1q deficiency is a rare genetic disorder. The C1q gene is located on the short arm of chromosome 1. So far, only a few mutations in C1q gene have been reported. The presence of these mutations is strongly associated with recurrent bacterial infections and the development of systemic lupus erythematosus(SLE). Recent clinical studies point to the significance of anti-C1q antibodies in the diagnosis and assessment of lupus nephritis activity.

Interpain A, a cysteine proteinase from Prevotella intermedia, inhibits complement by degrading complement factor C3

Periodontitis is an inflammatory disease of the supporting structures of the teeth caused by, among other pathogens, Prevotella intermedia. Many strains of P. intermedia are resistant to killing by the human complement system, which is present at up to 70% of serum concentration in gingival crevicular fluid. Incubation of human serum with recombinant cysteine protease of P. intermedia (interpain A) resulted in a drastic decrease in bactericidal activity of the serum. Furthermore, a clinical strain 59 expressing interpain A was more serum-resistant than another clinical strain 57, which did not express interpain A, as determined by Western blotting. Moreover, in the presence of the cysteine protease inhibitor E64, the killing of strain 59 by human serum was enhanced. Importantly, we found that the majority of P. intermedia strains isolated from chronic and aggressive periodontitis carry and express the interpain A gene. The protective effect of interpain A against serum bactericidal activity was found to be attributable to its ability to inhibit all three complement pathways through the efficient degradation of the alpha-chain of C3 -- the major complement factor common to all three pathways. P. intermedia has been known to co-aggregate with P. gingivalis, which produce gingipains to efficiently degrade complement factors. Here, interpain A was found to have a synergistic effect with gingipains on complement degradation. In addition, interpain A was able to activate the C1 complex in serum, causing deposition of C1q on inert and bacterial surfaces, which may be important at initial stages of infection when local inflammatory reaction may be beneficial for a pathogen. Taken together, the newly characterized interpain A proteinase appears to be an important virulence factor of P. intermedia.

Complex interactions with several arms of the complement system dictate innate and humoral immunity to adenoviral vectors

The complement system is known to play critical roles in pathogen identification, initiation of innate immune responses and facilitation of adaptive immune responses. Several studies have suggested that recombinant adenoviruses (rAds) interact with proteins of the complement system within minutes of administration. In this study, we assessed the roles of the alternative (Factor B), classical (C1q and C4) and common (C3) arms of the complement system in the innate and humoral response to systemic rAd administration using mice genetically deficient for each of these functions. Although most plasma cytokines and chemokines induced by Ads appeared to be elicited in a C3-dependent manner, we found that rAd-induced thrombocytopenia was dependent on Factor B and C3, implicating the alternative pathway as responsible for this response. Alteration of the complement-dependent transcriptome response after rAd-induced liver gene expression was also found to be Factor B- and C3-dependent. Ad interactions with the classical and alternative arms of the complement system can also be redundant, as many complement-dependent, Ad-induced innate immune responses appeared to be primarily C3-dependent. We also identified a C3 dependence of Ad-mediated induction of the nuclear factor-kappaB (NF-kappaB) activation pathway. Finally, we confirmed that humoral immune responses to the vector capsid, and the transgene it encodes, are also complement-dependent.

Short leucine-rich glycoproteins of the extracellular matrix display diverse patterns of complement interaction and activation

The extracellular matrix consists of structural macromolecules and other proteins with regulatory functions. An important family of the latter class of molecules found in most tissues is the small leucine-rich repeat proteins (SLRPs). We have previously shown that the SLRP fibromodulin binds directly to C1q and activates the classical pathway of complement. In the present study we further examine the interactions between SLRPs and complement. Osteoadherin, like fibromodulin, binds C1q and activates the classical pathway strongly while moderate activation is seen in the terminal pathway. This can be explained by the interaction of fibromodulin and osteoadherin with factor H, a major soluble inhibitor of complement. Also, chondroadherin was found to bind C1q and activate complement, albeit to a lesser extent. Chondroadherin also binds factor H. We confirm published data showing that biglycan and decorin bind C1q but do not activate complement. In this study a similar pattern is seen for lumican although its affinity for C1q is lower than for biglycan and decorin. Furthermore, using electron microscopy and radiolabeled SLRPs, we demonstrate two different classes of SLRP binding sites on C1q, to head and stalk respectively, where only binding to the head appears to be activating. We propose a role for SLRPs in the regulation of complement activation in diseases involving the extracellular matrix, particularly those characterized by chronic inflammation such as rheumatoid arthritis, atherosclerosis, osteoarthritis and chronic obstructive lung disease.

Cbln and C1q family proteins: new transneuronal cytokines

The C1q family is characterized by a C-terminal conserved global C1q domain, which is structurally very similar to the tumor necrosis factor homology domain. Although some C1q family members are expressed in the central nervous system, their functions have not been well characterized. Cbln1, a member of the Cbln subfamily of the C1q family, is predominantly expressed in cerebellar granule cells. Interestingly, Cbln1 was recently shown to play two unique roles at excitatory synapses formed between cerebellar granule cells and Purkinje cells: the formation and stabilization of synaptic contact, and the control of functional synaptic plasticity by regulating the postsynaptic endocytosis pathway. Since other Cbln subfamily members, Cbln2-Cbln4, are expressed in various regions of developing and mature brains, Cbln subfamily proteins may generally serve as a new class of transneuronal regulators of synapse development and synaptic plasticity in various brain regions.

[The association of complement with common connective tissue diseases - a review]

A strong association has been found between complement and common connective tissue diseases, such as systemic lupus erythema and Henoch Schoenlein Purpura. This has led to the notion that the pathogenesis of such diseases may involve a defect in the safe disposal of immune complexes, which is mediated by complement. To bring further light on this subject, a sensitive assay was developed to measure the ability of serum to prevent immune precipitation. This assay was then employed to study various Icelandic patient groups, and a defect in this function of complement was found to be common in patients with systemic lupus erythematosus and systemic sclerosis. Partial deficiency in complement C4A (C4A Q0) can not account for this defect, as it was not observed in patients with diabetes, gluten-sensitive enteropathy or autoimmune thyroiditis, in which C4A Q0 is common. The defect is strongly correlated with anti-C1q antibodies. Further studies are needed to test the possible role of anti-C1q antibodies in the pathogenesis of immune complex disease.

Complement protein C1q inhibits antibody-dependent enhancement of flavivirus infection in an IgG subclass-specific manner

Severe dengue virus infection can occur in humans with pre-existing antibodies against the virus. This observation led to the hypothesis that a subneutralizing antibody level in vivo can increase viral burden and cause more severe disease. Indeed, antibody-dependent enhancement of infection (ADE) in vitro has been described for multiple viruses, including the flaviviruses dengue virus and West Nile virus. Here, we demonstrate that the complement component C1q restricts ADE by anti-flavivirus IgG antibodies in an IgG subclass-specific manner in cell culture and in mice. IgG subclasses that avidly bind C1q induced minimal ADE in the presence of C1q. These findings add a layer of complexity for the analysis of humoral immunity and flavivirus infection.

Targeting classical complement pathway to treat complement mediated autoimmune diseases

Mice deficient for classical complement pathway (CCP) factor C4 are resistant to antibody and complement mediated experimental autoimmune myasthenia gravis (EAMG). Anti-C1q antibody administration before or following acetylcholine receptor immunization suppresses EAMG development by reducing lymph node cell IL-6 production and neuromuscular junction IgG, C3 and C5b-C9 deposition. This effect is achieved by treating mice with 10 microg of anti-C1q antibody, twice weekly for 4 weeks. Treatment with a higher amount of anti-C1q antibody gives rise to increased serum anti-acetylcholine receptor antibody, immune complex and C3 levels, facilitates kidney C3 and IgG deposits and thus reduces the treatment efficacy. C4 KO and anti-C1q antibody treated mice display normal immune system functions and intact antibody production capacity. Furthermore, CCP inhibition preserves alternative complement pathway activation, which is required for host defense against microorganisms. Therefore, CCP inhibition might constitute a specific treatment approach for not only myasthenia gravis but also other complement mediated autoimmune diseases.

Human astrovirus coat protein: a novel C1 inhibitor

C1 is a multimolecular complex that initiates the classical pathway of complement. It is composed of the pattern recognition component C1q and the serine proteases C1r and C1s. Activation of C1 elicits a series of potent effector mechanisms directed at limiting infection by invading pathogens as well as participating in other biological functions such as immune tolerance. While many molecules in addition to antibody have been demonstrated to activate C1, only a handful of C1 inhibitors have been described. Disregulated control of complement activation is associated with numerous autoimmune and inflammatory disease processes, thus tight regulation of C1 activation is highly desirable. We have recently discovered a novel inhibitor of C1, the coat protein of the human astroviruses, a family of enteric pathogens that infect young children. The astrovirus coat protein binds to the A-chain of C1q and inhibits spontaneous as well as antibody-mediated activation of the C1 complex resulting in suppression of classical pathway activation and complement-mediated terminal effector functions. This is the first description of a non-enveloped icosahedral virus inhibiting complement activation and the first description of a viral inhibitor of C1. The known inhibitors of C1 are reviewed and then discussed in the context of this novel viral C1 inhibitor. Additionally, the properties of this compound are elucidated highlighting its potential as an anti-complement therapeutic for the many diseases associated with inappropriate complement activation.

Anti-chromatin and anti-C1q antibodies in systemic lupus erythematosus compared to other systemic autoimmune diseases

OBJECTIVE

To evaluate the prevalence, sensitivity, and specificity of anti-chromatin and anti-C1q antibodies in systemic lupus erythematosus (SLE) and lupus nephritis compared to small vessel vasculitis and other connective tissue diseases. To provide long-term follow-up data for anti-chromatin antibodies in lupus nephritis.

METHODS

We determined the significance of anti-nuclear antibodies (ANA), anti- double-stranded DNA (anti-dsDNA), anti-chromatin, and anti-C1q antibodies, as well as complement factors C3 and C4, in relation to disease activity in SLE patients with (n = 47; long-term follow-up data for 33 patients) and without (n = 31) biopsy-confirmed lupus nephritis, microscopic polyangiitis (n = 37), Wegener's granulomatosis (n = 66), primary Sjögren's syndrome (n = 17), limited scleroderma (CREST syndrome) (n = 6), and progressive systemic scleroderma (PSS) (n = 11).

RESULTS

Anti-chromatin antibodies were more specific and sensitive than anti-C1q antibodies in distinguishing SLE patients from those with other systemic autoimmune diseases [anti-chromatin: sensitivity 64.1%, specificity 99.2%, odds ratio (OR) 219.6; anti-C1q: sensitivity 50%, specificity 72.6%, OR 2.65]. Anti-C1q antibodies were present in 75% of patients with Sjögren's syndrome and 35.1% of patients with microscopic polyangiitis. Anti-chromatin antibodies could identify SLE in patients with positive ANA but negative anti-dsDNA antibodies. Persisting anti-chromatin antibodies indicated SLE disease activity, even if anti-dsDNA antibodies had become negative. In long-term follow-up, those SLE patients with negative anti-dsDNA antibodies but persisting ANA and anti-chromatin antibodies relapsed if immunosuppression had been tapered. Anti-chromatin antibodies correlated with the SLE disease activity index (SLEDAI) as a marker of disease activity.

CONCLUSIONS

The measurement of anti-chromatin, but not anti-C1q, antibodies in patients with systemic autoimmune diseases increases diagnostic sensitivity and specificity for SLE and assists in treatment decisions in anti-dsDNA-negative patients.

Fc receptor but not complement binding is important in antibody protection against HIV

Most successful vaccines elicit neutralizing antibodies and this property is a high priority when developing an HIV vaccine. Indeed, passively administered neutralizing antibodies have been shown to protect against HIV challenge in some of the best available animal models. For example, antibodies given intravenously can protect macaques against intravenous or mucosal SHIV (an HIV/SIV chimaera) challenge and topically applied antibodies can protect macaques against vaginal SHIV challenge. However, the mechanism(s) by which neutralizing antibodies afford protection against HIV is not understood and, in particular, the role of antibody Fc-mediated effector functions is unclear. Here we report that there is a dramatic decrease in the ability of a broadly neutralizing antibody to protect macaques against SHIV challenge when Fc receptor and complement-binding activities are engineered out of the antibody. No loss of antibody protective activity is associated with the elimination of complement binding alone. Our in vivo results are consistent with in vitro assays indicating that interaction of Fc-receptor-bearing effector cells with antibody-complexed infected cells is important in reducing virus yield from infected cells. Overall, the data suggest the potential importance of activity against both infected cells and free virus for effective protection against HIV.

C1q nephropathy in a 2-year-old boy presenting with steroid resistant nephrotic syndrome

We experienced a case of a 2-year-old boy, who presented with steroid resistant nephrotic syndrome, which developed insidiously. Renal biopsy revealed that he had focal and segmental glomerulosclerosis on light microscopy, dominant mesangial deposition of C1q by immunofluorescent staining, and electron dense deposits on electron microscopy, which are all compatible with C1q nephropathy. He had no clinical sign of any collagen diseases, including systemic lupus erythematodes. So, the diagnosis of C1q nephropathy was made. An intensive treatment by a combination of cyclosporine, prednisolone and methylprednisolone pulse therapy was successful in achieving remission and disappearance of proteinuria in this patient. Although he developed hypertension requiring calcium blocker and angiotensin converting enzyme inhibitor, his renal function stayed within normal limit for 3 years after the initiation of the treatment. The growth was well preserved during the 3 years of treatment with almost unchanged SD scores for height. He has delay in speech, which may not be associated with the etiology of his nephropathy, based on the absence of such association in the previous reports. C1q nephropathy is still a controversial clinical entity, so accumulation of the cases may help further understand the pathogenesis and clinical manifestation of C1q nephropathy.

Urticarial vasculitis

Urticarial vasculitis can present in a variety of ways, ranging from a primarily cutaneous disease consisting of chronic urticaria to a lupus-like disease with severe cardiopulmonary disease. Low complement levels and positive anti-C1q antibodies are markers of more severe disease. Care must be taken to look for an underlying condition. The mainstay of therapy is treatment of any underlying condition. Therapies most often employed include corticosteroids, antihistamine, and dapsone, but many others have been utilized.

A novel role of complement factor C1q in augmenting the presentation of antigen captured in immune complexes to CD8+ T lymphocytes

Ag-IgG immune complexes (IC) are efficiently taken up, and Ag-derived peptides are subsequently processed and presented by APC. In vitro experiments indicate that IgG Fc Receptors (FcgammaR) facilitate the efficient uptake of IC by dendritic cells. Previous experiments showed that the cross-presentation of Ag-derived peptides after s.c. administration of IC is FcgammaR-dependent. To study the role of different FcgammaR and complement in MHC class I Ag presentation after i.v. administration, we used mice deficient for FcgammaRs and complement components. These mice were injected with CFSE-labeled OVA-specific CD8+ T cells followed by administration of IC composed of OVA and rabbit anti-OVA IgG i.v. to measure MHC class I presentation of OVA-derived peptides. The Ag presentation was partly reduced in FcRgamma-chain-deficient mice, but not affected in FcgammaRI/II/III-deficient mice, complement factor C3-deficient mice, or FcgammaRI/II/III x C3-deficient mice. Importantly, CD8+ T cell proliferation was significantly reduced in mice deficient for C1q. This proliferation could be restored when IC were incubated with purified human C1q before injection. Likewise, purified C1q could strongly enhance the uptake and presentation of IC by dendritic cells in vitro. Heat inactivation abrogated the C1q-mediated uptake of IC. In addition, in vivo uptake of OVA-IC in the spleen was significantly reduced in C1q-deficient mice compared with wild-type mice. Together, these results indicate a novel function of C1q, which is present in high levels in the bloodstream, by directly enhancing the uptake and MHC class I presentation of Ag captured in IC by APC to CD8+ T cells.