Decoding the Human Immunoglobulin G-Glycan Repertoire Reveals a Spectrum of Fc-Receptor- and Complement-Mediated-Effector Activities.

Glycosylation of the immunoglobulin G (IgG)-Fc tail is required for binding to Fc-gamma receptors (FcγRs) and complement-component C1q. A variety of IgG1-glycoforms is detected in human sera. Several groups have found global or antigen-specific skewing of IgG glycosylation, for example in autoimmune diseases, viral infections, and alloimmune reactions. The IgG glycoprofiles seem to correlate with disease outcome. Additionally, IgG-glycan composition contributes significantly to Ig-based therapies, as for example IVIg in autoimmune diseases and therapeutic antibodies for cancer treatment. The effect of the different glycan modifications, especially of fucosylation, has been studied before. However, the contribution of the 20 individual IgG glycoforms, in which the combined effect of all 4 modifications, to the IgG function has never been investigated. Here, we combined six glyco-engineering methods to generate all 20 major human IgG1-glycoforms and screened their functional capacity for FcγR and complement activity. Bisection had no effect on FcγR or C1q-binding, and sialylation had no- or little effect on FcγR binding. We confirmed that hypo-fucosylation of IgG1 increased binding to FcγRIIIa and FcγRIIIb by ~17-fold, but in addition we showed that this effect could be further increased to ~40-fold for FcγRIIIa upon simultaneous hypo-fucosylation and hyper-galactosylation, resulting in enhanced NK cell-mediated antibody-dependent cellular cytotoxicity. Moreover, elevated galactosylation and sialylation significantly increased (independent of fucosylation) C1q-binding, downstream complement deposition, and cytotoxicity. In conclusion, fucosylation and galactosylation are primary mediators of functional changes in IgG for FcγR- and complement-mediated effector functions, respectively, with galactose having an auxiliary role for FcγRIII-mediated functions. This knowledge could be used not only for glycan profiling of clinically important (antigen-specific) IgG but also to optimize therapeutic antibody applications.

Systemic complement activation in central serous chorioretinopathy.

PURPOSE: A clear link between several variants in genes involved in the complement system and chronic central serous chorioretinopathy (CSC) has been described. In age-related macular degeneration, a disease that shows clinical features that overlap with CSC, both genetic risk factors and systemic activation of the complement system have previously been found. In this case-control study, we assessed whether there is evidence of either systemic activation or inhibition of the complement system in patients with chronic CSC. METHODS: A prospective case-control study of 76 typical chronic CSC patients and 29 controls without ophthalmological history was conducted. Complement activity assays (classical, alternative, and mannose-binding lectin pathway), complement factors 3, 4, 4A, 4B, B, D, H, I, and P, activation products C3d, C5a, and sC5b-C9, and the C3d/C3 ratio were analysed in either serum or plasma. A correction for possible effects of gender, age, body mass index, and smoking status was performed. RESULTS: In this study, none of the tested variables, including regulation and activation products, proved to be significantly different between the groups. Moreover, no associations with either CSC disease activity or possible CSC related steroid use were observed. CONCLUSION: Despite the available literature regarding a possible relationship between chronic CSC and variants in genes involved in the complement system, we did not find evidence of an association of chronic CSC with either systemic complement activation or inhibition.

The High Prevalence of Functional Complement Defects Induced by Chemotherapy.

INTRODUCTION: To date, oncology patients are more dependent on non-cellular host defense against pathogens due to intensive (chemo)therapy-related bone marrow suppression. Since data on complement functionality in oncology patients are limited, we aimed to investigate the innate complement function in relation to the type of malignancy and therapy in a longitudinal cohort of patients. METHODS: A large single-center, prospective non-intervention study was conducted, in which blood samples were taken from patients before, during, and after treatment with chemotherapy and/or subsequent admittance for (febrile) neutropenia. RESULTS/FINDINGS: Analysis of 48 patients showed a high percentage of defects in complement activity of the alternative pathway (19.1%), the classical pathway (4.3%), or both (42.6%). Post hoc analysis of six different treatment protocols with more than three patients each showed distinct effects of specific therapies. Whereas patients treated according to the Ewing, EpSSG-rhabdomyosarcoma, or SIOP CNS germ cell tumor protocol showed no defects, patients treated according to the ALL-11 (leukemia), the EURAMOS I (osteosarcoma), or the ACNS (medulloblastoma) protocols showed an almost universal reduction in complement function. Although we could not explain the reduced complement functionality under all conditions, a strong effect was observed following high-dose methotrexate or ifosfamide. CONCLUSION: Acquired complement defects were commonly observed in more than 50% of oncology patients, some of which associated with certain chemotherapeutic drugs. Additional studies are needed to determine the clinical and therapeutic context of complement defects and their possible effect on treatment outcome or the increased risk of infection.

Nebulized C1-Esterase Inhibitor does not Reduce Pulmonary Complement Activation in Rats with Severe Streptococcus Pneumoniae Pneumonia.

Complement activation plays an important role in the pathogenesis of pneumonia. We hypothesized that inhibition of the complement system in the lungs by repeated treatment with nebulized plasma-derived human C1-esterase inhibitor reduces pulmonary complement activation and subsequently attenuates lung injury and lung inflammation. This was investigated in a rat model of severe Streptococcus pneumoniae pneumonia. Rats were intra-tracheally challenged with S. pneumoniae to induce pneumonia. Nebulized C1-esterase inhibitor or saline (control animals) was repeatedly administered to rats, 30 min before induction of pneumonia and every 6 h thereafter. Rats were sacrificed 20 or 40 h after inoculation with bacteria. Brochoalveolar lavage fluid and lung tissue were obtained for measuring levels of complement activation (C4b/c), lung injury and inflammation. Induction of pneumonia was associated with pulmonary complement activation (C4b/c at 20 h 1.24 % [0.56-2.59] and at 40 h 2.08 % [0.98-5.12], compared to 0.50 % [0.07-0.59] and 0.03 % [0.03-0.03] in the healthy control animals). The functional fraction of C1-INH was detectable in BALF, but no effect was found on pulmonary complement activation (C4b/c at 20 h 0.73 % [0.16-1.93] and at 40 h 2.38 % [0.54-4.19]). Twenty hours after inoculation, nebulized C1-esterase inhibitor treatment reduced total histology score, but this effect was no longer seen at 40 h. Nebulized C1-esterase inhibitor did not affect other markers of lung injury or lung inflammation. In this negative experimental animal study, severe S. pneumoniae pneumonia in rats is associated with pulmonary complement activation. Repeated treatment with nebulized C1-esterase inhibitor, although successfully delivered to the lungs, does not affect pulmonary complement activation, lung inflammation or lung injury.

Myocardial infarction induces atrial inflammation that can be prevented by C1-esterase inhibitor.

AIMS: Inflammation plays an important role in the pathogenesis of myocardial infarction (MI). Whether MI induces atrial inflammation is unknown however. Here, we analysed atrial inflammation in patients with MI and in rats with experimentally induced MI. The effect of the anti-inflammatory agent C1-esterase inhibitor (C1inh) on atrial inflammation in rats was also analysed. METHODS: In the hearts of patients who died at different time points after MI (total n=24, mean age=60), neutrophils (myeloperoxidase-positive cells), lymphocytes (CD45-positive cells) and macrophages (CD68-positive cells) were quantified in the myocardium of the left and right atria and the infarcted left and non-infarcted right ventricles and compared with control patients (n=5, mean age=59). For the left and right atria, inflammatory cells were also quantified in the atrial adipose tissue. MI was induced in 17 rats, of which 10 were subsequently treated with C1inh for 6 days. Forty-two days post-MI, lymphocytes, macrophages and the endothelial inflammation marker Nε-(carboxymethyl)lysine (CML) were analysed in the myocardium of both the atria and ventricles. RESULTS: In all investigated areas of the human hearts increased lymphocytes and macrophages were observed to a varying extent, especially between 6 h and 5 days following MI. Similarly, in rats MI resulted in an increase of inflammatory cells and CML in the atria. C1inh treatment decreased atrial inflammation. CONCLUSIONS: MI induces atrial inflammation in patients and in rats. C1inh treatment could counteract this MI-induced atrial inflammation in rats.

Salivary agglutinin is the major component in human saliva that modulates the lectin pathway of the complement system.

Saliva interacts with blood after mucosal damage or leakage of gingival crevicular fluid. Surface-adsorbed salivary agglutinin (SAG) activates the lectin pathway (LP) of the complement system via mannose-binding lectin, while SAG in solution inhibits complement activation. In the present study we investigated if, next to SAG, whole and glandular saliva itself and other salivary glycoproteins activate or inhibit the LP. Complement activation was measured by detecting C4 deposition on microtiter plates coated with saliva or purified proteins. Complement inhibition was measured after incubating serum with saliva or proteins in microtiter plates coated with mannan, an LP activator. Adsorbed whole, sublingual and submandibular saliva showed LP-dependent complement activation. Blood group secretors, but not non-secretors, activated the LP. Saliva of both secretors and non-secretors inhibited C4 deposition on mannan. After depletion of SAG, saliva no longer inhibited the LP. Other salivary proteins, including amylase, MUC5B and histatin 2, did not activate or inhibit the LP. Surface-adsorbed whole saliva and glandular saliva samples activate the LP of complement, depending on the presence of SAG and the secretor status of the donor. In solution, saliva inhibits the LP, depending on the presence of SAG, but independent of the secretor status.

Activated protein C inhibits neutrophil migration in allergic asthma: a randomised trial.

Asthma patients show evidence of a procoagulant state in their airways, accompanied by an impaired function of the anticoagulant protein C system. We aimed to study the effect of recombinant human activated protein C (rhAPC) in allergic asthma patients.We conducted a randomised, double-blind, placebo-controlled, proof-of-concept study in house dust mite (HDM) allergic asthma patients. Patients were randomised to receive intravenous rhAPC (24 µg·kg(-1)·h(-1); n=12) or placebo (n=12) for 11 h. 4 h after the start of infusion, a first bronchoscopy was performed to challenge one lung segment with saline (control) and a contralateral segment with a combination of HDM extract and lipopolysaccharide (HDM+LPS), thereby mimicking environmental house dust exposure. A second bronchoscopy was conducted 8 h after intrabronchial challenge to obtain bronchoalveolar lavage fluid (BALF).rhAPC did not influence HDM+LPS induced procoagulant changes in the lung. In contrast, rhAPC reduced BALF leukocyte counts by 43% relative to placebo, caused by an inhibitory effect on neutrophil influx (64% reduction), while leaving eosinophil influx unaltered. rhAPC also reduced neutrophil degranulation products in the airways.Intravenous rhAPC attenuates HDM+LPS-induced neutrophil migration and protein release in allergic asthma patients by an effect that does not rely on coagulation inhibition.

An improved monocyte activation test using cryopreserved pooled human mononuclear cells.

The monocyte activation test (MAT) is a promising replacement of the currently used rabbit pyrogen test to detect the presence of pyrogens in injectable drugs. In the MAT, drugs are incubated with a source of human monocytes and production of pyrogenic cytokines used as readout. The best results are obtained with human mononuclear cells (MNC). However, donor variation requires testing on four different donors, and for most laboratories access to fresh MNCs is a problem. The current study shows how to overcome these problems using frozen pooled MNCs. The MAT is performed by thawing pooled MNC and co-culture overnight with a test substance, LPS or non-endotoxin pyrogens, with IL-6 production as the readout. The study demonstrates that fresh and frozen pooled MNC have comparable sensitivity. The reproducibility of the MAT performed with different batches of frozen pooled MNC was excellent. Different non-endotoxin pyrogens induce IL-6, confirming the ability of the MAT to detect a variety of pyrogens. In conclusion, the MAT using frozen pooled MNC is a highly sensitive, specific and reproducible pyrogen test, able to detect and quantify endotoxin and non-endotoxin pyrogenic contaminations in parenteral pharmaceuticals.

Complement activation by salivary agglutinin is secretor status dependent.

After mucosal damage or gingival inflammation, complement proteins leak into the oral cavity and mix with salivary proteins such as salivary agglutinin (SAG/gp-340/DMBT1). This protein is encoded by the gene Deleted in Malignant Brain Tumors 1 (DMBT1), and it aggregates bacteria, viruses and fungi, and activates the lectin pathway of the complement system. In the lectin pathway, carbohydrate structures on pathogens or altered self cells are recognized. SAG is highly glycosylated, partly on the basis of the donor's blood group status. Whereas secretors express Lewis b, Lewis y, and antigens from the ABO-blood group system on SAG, non-secretors do not. Through mannose-binding lectin (MBL) binding and C4 deposition assays, we aimed to identify the chemical structures on SAG that are responsible for complement activation. The complement-activating properties of SAG were completely abolished by oxidation of its carbohydrate moiety. SAG-mediated activation of complement was also inhibited in the presence of saccharides such as fucose and Lewis b carbohydrates, and also after pretreatment with the fucose-binding lectin, Anguilla anguilla agglutinin. Complement activation was significantly (p<0.01) higher in secretors than in non-secretors. Our results suggest that fucose-rich oligosaccharide sidechains, such as Lewis b antigens, are involved in the activation of complement by SAG.

Lymphocytes infiltrate the quadriceps muscle in lymphocytic myocarditis patients: a potential new diagnostic tool.

BACKGROUND: Diagnosing lymphocytic myocarditis (LM) is challenging because of the large variation in clinical presentation and the limitations inherent in current diagnostic tools. The objective of this study was to analyze infiltration of inflammatory cells in quadriceps skeletal muscle of LM patients and investigate the potential diagnostic value of assaying infiltrating inflammatory cells. METHODS: Quadriceps muscle tissue, obtained at autopsy from control patients (n = 9) and LM patients (n = 21), was analyzed using immunohistochemistry for infiltration of lymphocytes (CD45), macrophages (CD68), neutrophilic granulocytes (myeloperoxidase), and several lymphocyte subtypes (CD3, CD4, CD8, CD20) and using polymerase chain reaction for a panel of myocarditis-associated viruses. Additionally, quadriceps muscle from mice with acute coxsackievirus B3-induced myocarditis and control mice was analyzed for presence of lymphocytes and virus. RESULTS: In quadriceps muscle of LM patients the number of infiltrating lymphocytes were significantly increased and LM was diagnosed with specificity of 100% and sensitivity of 71%. Parvovirus B19 was the primary virus found in our patient groups, found in quadriceps tissue of 3 LM patients (although it was also found in 1 control patient). In the mice, enteroviral RNA was present in the quadriceps muscle, although enteroviral capsid proteins and lymphocyte infiltration were found primarily in the adipose tissue within and directly adjacent to the myocyte tissue, rather than in the myocyte tissue itself. CONCLUSIONS: LM is associated with lymphocyte infiltration and viral presence in quadriceps muscle. This indicates that skeletal muscle biopsy/lymphocyte quantification might be a potential diagnostic tool for LM patients.

Functional analysis of the anti-adalimumab response using patient-derived monoclonal antibodies.

The production of antibodies to adalimumab in autoimmune patients treated with adalimumab is shown to diminish treatment efficacy. We previously showed that these antibodies are almost exclusively neutralizing, indicating a restricted response. Here, we investigated the characteristics of a panel of patient-derived monoclonal antibodies for binding to adalimumab. Single B-cells were isolated from two patients, cultured, and screened for adalimumab specificity. Analysis of variable region sequences of 16 clones suggests that the immune response against adalimumab is broad, involving multiple B-cell clones each using different combinations of V(D)J segments. A strong bias for replacement mutations in the complementarity determining regions was found, indicating an antigen-driven response. We recombinantly expressed 11 different monoclonal antibodies and investigated their affinity and specificity. All clones except one are of high affinity (Kd between 0.6 and 233 pm) and compete with TNF as well as each other for binding to adalimumab. However, binding to a panel of single-point mutants of adalimumab indicates markedly different fine specificities that also result in a differential tendency of each clone to form dimeric and multimeric immune complexes. We conclude that although all anti-adalimumab antibodies compete for binding to TNF, the response is clonally diverse and involves multiple epitopes on adalimumab. These results are important for understanding the relationship between self and non-self or idiotypic determinants on therapeutic antibodies and their potential immunogenicity.

The minipig as an alternative non-rodent model for immunogenicity testing using the TNFα blockers adalimumab and infliximab.

Immunogenicity is a major issue of concern for monoclonal antibodies used in human diseases and is by default mainly determined in non-human primates (NHP), as target molecules are considered most similar in NHP compared to human. In this manuscript the predictive value of immunogenicity testing in minipigs for human safety is evaluated, as the immune system of the pig is functionally similar to that in other mammalian species. Adalimumab and infliximab (both monoclonal antibodies blocking TNFα) were used as model substances. Female Göttingen minipigs (4/group) were treated every other week with low (0.1 mg/kg), mid (1.0 mg/kg), or high dose (5 mg/kg) adalimumab or 5 mg/kg infliximab subcutaneous (SC) over a period of 8 weeks. After first and last dosing, pharmacokinetic analysis was performed. Anti-drug antibodies (ADAs) were measured on several time points. Furthermore, hematology, clinical chemistry, body weight, clinical signs, and histopathology of several organs were evaluated. No signs of toxicity of the treatments were observed in the limited organs and tissues collected. Eleven out of 12 minipigs treated with adalimumab elicited a detectable ADA response. Induction of ADA was correlated with decreased plasma levels of adalimumab. Infliximab clearance was comparable after first and last dose. Therefore, the presence of ADA directed to infliximab was considered highly unlikely. It was concluded that the minipig and NHP showed comparable suitability for immunogenicity prediction in humans. More studies with other biopharmaceutical products are needed to strengthen the status of the minipig as an alternative model for immunotoxicity testing including immunogenicity.

Plasma-derived mannose-binding lectin shows a direct interaction with C1-inhibitor.

MBL-deficiency has been associated with an increased frequency and severity of infection, in particular in children and under immunocompromized conditions. In an open uncontrolled safety and pharmacokinetic MBL-substitution study using plasma-derived MBL (pdMBL) in MBL-deficient pediatric oncology patients, we found that despite MBL trough levels above 1.0µg/ml MBL functionality was not efficiently restored upon ex vivo testing. PdMBL showed C4-converting activity by itself, indicating the presence of MASPs. Upon incubation of pdMBL with MBL-deficient sera this C4-converting activity was significantly reduced. Depletion of the MASPs from pdMBL, paradoxically, restored the C4-converting activity. Subsequent depletion or inhibition of C1-inh, the major inhibitor of the lectin pathway, in the recipient serum restored the C4-converting activity as well. Complexes between MBL/MASPs and C1-inh (MMC-complexes) were detected after ex vivo substitution of MBL-deficient serum with pdMBL. These MMC-complexes could also be detected in the sera of the patients included in the MBL-substitution study shortly after pdMBL infusion. Altogether, we concluded that active MBL-MASP complexes in pdMBL directly interact with C1-inh in the recipient, leading to the formation of a multimolecular complex between C1-inh and MBL/MASPs, in contrast to the classical pathway where C1r and C1s are dissociated from C1q by C1-inh. Because of the presence of activated MASPs in the current pdMBL products efficient MBL-mediated host protection cannot be expected because of the neutralizing capacity by C1-inh.

Blood plasma inflammation markers during epileptogenesis in post-status epilepticus rat model for temporal lobe epilepsy.

PURPOSE: Brain inflammation occurs during epileptogenesis and may contribute to the development and progression of temporal lobe epilepsy. Recently, several studies have indicated that seizures may also increase specific blood plasma cytokine levels in animal models as well as in human patients with epilepsy, suggesting that peripheral inflammation may serve as a biomarker for epilepsy. Moreover, studies in epilepsy animal models have shown that peripheral inflammation may play either a pathogenic or neuroprotective role. METHODS: We evaluated the inflammatory response in blood plasma after electrically induced status epilepticus (SE) in a rat model for temporal lobe epilepsy. We measured blood plasma levels of the inflammation markers interleukin 1ß (IL-1ß), interleukin 6 (IL-6), by enzyme-linked immunosorbent assays (ELISAs) and C-reactive protein (CRP) by immunoturbidimetry, at 1 day after SE (acute period), at 1 week (during the latent period), and at 2 months after SE, which is the chronic epileptic phase when spontaneous seizures occur. Plasma levels were also measured during pilocarpine-induced SE. These were compared with plasma levels after lipopolysaccharide injection, which causes sepsis. KEY FINDINGS: Although sepsis induced a huge surge in IL-1ß and IL-6 levels, we did not detect a change in IL-1ß, IL-6, or CRP plasma levels at any time point after electrically induced SE compared to control animals. SE induced by pilocarpine produced a rise in IL-6 and CRP but not IL-1ß levels. SIGNIFICANCE: These findings suggest that plasma levels of these inflammatory proteins cannot be used as biomarkers for temporal lobe epileptogenesis.

Adalimumab elicits a restricted anti-idiotypic antibody response in autoimmune patients resulting in functional neutralisation.

OBJECTIVES: Millions of patients worldwide are treated with therapeutic monoclonal antibodies. These biological therapeutics can be immunogenic, resulting in anti-drug antibody formation which leads to loss of response. Fully human biological agents, such as the anti-tumour necrosis factor α (anti-TNFα) antibody adalimumab, are considered to be weakly immunogenic, but anti-adalimumab antibodies (AAA) were recently detected in more than half of treated patients with rheumatoid arthritis (RA) within 28 weeks of treatment. A study was undertaken to determine the mechanism by which AAA lead to loss of response. METHODS: The specificity of the repertoire of AAA was investigated in a cohort of 50 AAA-positive RA patients. Inhibition experiments using TNFα and patient-derived anti-adalimumab monoclonal antibodies were performed. RESULTS: The antibody response against adalimumab is highly restricted: Fab fragments of a single monoclonal antibody specific for the idiotype of adalimumab inhibited 98.65% (25th-75th percentiles: 98.25-99.90) of the total anti-adalimumab reactivity in serum from 50 AAA-positive patients. The anti-adalimumab response was confined to the TNFα binding region of adalimumab, thereby neutralising its therapeutic efficacy. In line with this restricted specificity, small immune complexes were found in the circulation of AAA-forming patients. CONCLUSIONS: The humoral immune response against adalimumab is highly restricted and limited to the idiotype of the therapeutic antibody. All antibodies result in functional neutralisation of the drug, thereby providing a mechanism by which AAA formation leads to clinical non-response.

C1-esterase inhibitor protects against early vein graft remodeling under arterial blood pressure.

OBJECTIVES: Arterial pressure induced vein graft injury can result in endothelial loss, accelerated atherosclerosis and vein graft failure. Inflammation, including complement activation, is assumed to play a pivotal role herein. Here, we analyzed the effects of C1-esterase inhibitor (C1inh) on early vein graft remodeling. METHODS: Human saphenous vein graft segments (n=8) were perfused in vitro with autologous blood either supplemented or not with purified human C1inh at arterial pressure for 6h. The vein segments and perfusion blood were analyzed for cell damage and complement activation. In addition, the effect of purified C1inh on vein graft remodeling was analyzed in vivo in atherosclerotic C57Bl6/ApoE3 Leiden mice, wherein donor caval veins were interpositioned in the common carotid artery. RESULTS: Application of C1inh in the in vitro perfusion model resulted in significantly higher blood levels and significantly more depositions of C1inh in the vein wall. This coincided with a significant reduction in endothelial loss and deposition of C3d and C4d in the vein wall, especially in the circular layer, compared to vein segments perfused without supplemented C1inh. Administration of purified C1inh significantly inhibited vein graft intimal thickening in vivo in atherosclerotic C57Bl6/ApoE3 Leiden mice, wherein donor caval veins were interpositioned in the common carotid artery. CONCLUSION: C1inh significantly protects against early vein graft remodeling, including loss of endothelium and intimal thickening. These data suggest that it may be worth considering its use in patients undergoing coronary artery bypass grafting.

The bacteria binding glycoprotein salivary agglutinin (SAG/gp340) activates complement via the lectin pathway.

Salivary agglutinin (SAG), also known as gp-340 and Deleted in Malignant Brain Tumours 1, is a glycoprotein that is present in tears, lung fluid and mucosal surfaces along the gastrointestinal tract. It is encoded by the Deleted in Malignant Brain Tumours 1 gene, a member of the Scavenger Receptor Cysteine Rich group B protein superfamily. SAG aggregates bacteria thus promoting their clearance from the oral cavity and activates the complement system. Complement proteins may enter the oral cavity in case of serum leakage, which occurs after mucosal damage. The purpose of this study was to investigate the mode of complement activation. We showed a dose-dependent C4 deposition on SAG-coated microplates showing that either the classical or lectin pathway of complement was activated. Antibodies against mannose binding lectin inhibited C4 deposition and SAG induced no C4 deposition in MBL deficient sera showing SAG activated complement through the MBL pathway. Periodate treatment of SAG abolished MBL pathway activation consistent with an involvement of SAG glycans in complement activation. This provides the first evidence for a role of SAG in complement activation through the MBL pathway and suggests a potential role of SAG as a complement activating factor at the mucosal epithelia.

Analysis of apoptosis in peripheral blood and synovial tissue very early after initiation of infliximab treatment in rheumatoid arthritis patients.

OBJECTIVE: Infliximab treatment results in a decrease in synovial cellularity as early as 48 hours after initiation of therapy in patients with rheumatoid arthritis (RA). This study was undertaken to investigate whether infliximab induces apoptosis within the first 24 hours after infusion. METHODS: The percentage of apoptotic cells was determined by flow cytometry in blood drawn from 21 patients directly before, 1 hour after, and 24 hours after infliximab infusion. Synovial tissue samples obtained before, 1 hour after (n = 5), or 24 hours after (n = 5) initiation of therapy were subjected to immunohistochemistry to detect active caspase 3 and to TUNEL assay and electron microscopy to detect apoptosis. In addition, plasma levels of nucleosomes (generated during apoptosis) and C4b/c (an indicator of complement activation) were measured. RESULTS: There were no signs of apoptosis induction in peripheral blood monocytes or lymphocytes after infliximab treatment. Circulating lymphocyte counts were increased within 1 hour after infusion (P < 0.05). There was no definite evidence of apoptosis induction in the synovium, except in 1 patient 24 hours after the infliximab infusion. Consistent with these results, there was no increase in nucleosome levels nor were there signs of complement activation. CONCLUSION: Our findings indicate that the rapid decrease in synovial cellularity observed after initiation of anti-tumor necrosis factor antibody therapy cannot be explained by apoptosis induction at the site of inflammation. It is tempting to speculate that the striking effects on synovial inflammation may be explained by other mechanisms, such as decreased migration toward the synovial compartment and reduced retention in the inflamed synovium.

C1 inhibitor: just a serine protease inhibitor? New and old considerations on therapeutic applications of C1 inhibitor.

C1 inhibitor is a potent anti-inflammatory protein as it is the major inhibitor of proteases of the contact and the complement systems. C1-inhibitor administration is an effective therapy in the treatment of patients with hereditary angioedema (HAE) who are genetically deficient in C1 inhibitor. Owing to its ability to modulate the contact and complement systems and the convincing safety profile, plasma-derived C1 inhibitor is an attractive therapeutic protein to treat inflammatory diseases other than HAE. In the present review we give an overview of the biology of C1 inhibitor and its use in HAE. Furthermore, we discuss C1 inhibitor as an experimental therapy in diseases such as sepsis and myocardial infarction.

Complexes between C1q and C3 or C4: novel and specific markers for classical complement pathway activation.

Classical pathway activation is often assessed by measuring circulating levels of activated C4. However, this parameter does not discriminate between activation through the classical or the lectin pathway. We hypothesized that during classical pathway activation, complexes are formed between C1q and activated C4 or C3. Using ELISA, we investigated whether such complexes constitute specific markers for classical pathway activation. In vitro, C1q-C3d/C4d complexes were generated upon incubation of normal recalcified plasma with aggregated IgG or an anti-C1q mAb that activates C1 (mAb anti-C1q-130). In contrast, during incubation with C1s or trypsin, C1q-C3d/C4d complexes were not generated, which excludes an innocent bystander effect. Additionally, C1q-C3d/C4d complexes were not generated during activation of the alternative or the lectin pathway. Repeated freezing and thawing did not influence levels of C1q-C3d/C4d complexes in recalcified plasma. To measure C1q-complement complexes in plasma samples, we separated unbound complement proteins from C1q-C3d/C4d complexes in the samples prior to testing with ELISA. In samples from patients undergoing cardiopulmonary bypass surgery or suffering from rheumatoid arthritis, we found higher levels of C1q-C4 complexes than in samples from healthy individuals. We conclude that complexes between C1q and C4 or C3 are specific markers of classical complement pathway activation.