In vitro comparison of the complement-scavenging capacity of different intravenous immunoglobulin preparations

Background and Objectives  Complement inhibition is considered important in the mechanism of action of intravenous immunoglobulin (IVIG) in a number of inflammatory and autoimmune disorders. The capacity of different IVIG preparations to 'scavenge' activated C3 and thereby inhibit complement activation was assessed by a new in vitro assay.
Materials and Methods  Diluted human serum as a complement source, with or without addition of different concentrations of IVIG, was incubated in microtitre plates coated with heat-aggregated human IgG. Complement scavenging was measured by detecting reduced C3 binding and determining fluid phase C3b–IgG complex formation. Complement activation induced by the IVIG preparations was measured as C5a formation.
Results  All IVIG preparations exhibited a dose-dependent inhibition of C3b deposition, correlating strongly with binding of C3b to fluid-phase IgG, but the extent of complement scavenging varied considerably between different IVIG preparations. At an IVIG concentration of 0·9 mg/ml, the inhibition of C3b deposition ranged from 72 ± 16% to 22 ± 4·1%. The reduction of C3b deposition on the complement-activating surface was not due to IVIG-induced complement activation in the fluid phase, as shown by the low C5a formation in the presence of serum.
Conclusion  In vitro analysis allows comparison of the complement-inhibitory properties of IVIG preparations. The extent of complement scavenging varies between the products.     

Accelerated autoantibody clearance by intravenous immunoglobulin therapy: studies in experimental models to determine the magnitude and time course of the effect.

Recently, it has been postulated that the beneficial effect of intravenous immunoglobulins (IVIGs) in antibody-mediated autoimmune disorders is based on accelerated catabolism of autoantibodies. In the current study, in vivo experiments were performed with mice in which autoantibody production was mimicked by continuous infusion of monoclonal antibodies. In this model, a single dose of IVIG reduced the plasma concentrations of the infused immunoglobulin (Ig)G1 monoclonal antibody (mAb) by approximately 40% after 3 days, whereas the concentration of an IgA mAb was not affected. To extrapolate these findings to humans, a computational model for IgG clearance was established that accurately predicted the time course and magnitude of the decrease in IgG plasma levels observed in mice. Adapted for humans, this model predicted a gradually occurring decrease in autoantibody levels after IVIG administration (2 g/kg), with a maximum reduction of approximately 25% after 3 to 4 weeks and a continued decrease of several months. In conclusion, a single high dose of IVIG induces a relatively small but long-lasting reduction of autoantibody levels by accelerated IgG clearance. This mechanism has clinical relevance in the sense that it can fully explain, as the sole mechanism, the gradual decrease in autoantibody levels observed in several patient studies. However, in some clinical studies, larger or more rapid effects have been observed that cannot be explained by accelerated clearance. Hence, IVIG can also reduce autoantibody levels through mechanisms such as down-regulation of antibody production or neutralization by anti-idiotypic antibodies.     

Protein synthesis in liver following infusion of the catabolic hormones corticosterone, epinephrine, and glucagon in rats

The mediator(s) and mechanism(s) of acute-phase protein synthesis in the liver following injury and sepsis are not fully known. Elevated plasma levels of the catabolic hormones cortisol, glucagon, and epinephrine have been reported in trauma and sepsis. In previous reports, when these hormones were infused simultaneously (triple hormone infusion), several, but not all, of the metabolic alterations characteristic of sepsis occurred. In the current investigation, the effect of triple hormone infusion on hepatic protein synthesis was studied. Rats were infused intravenously during 16 hours with a solution containing corticosterone (4.2 mg/kg/h), glucagon (2.5 micrograms/kg/h), and epinephrine (6 micrograms/kg/h). Control animals were infused with a corresponding volume of vehicle. Total hepatic protein synthesis in vivo was measured with a flooding dose technique using [14C]-leucine. The synthesis of total secretory proteins and of the individual proteins albumin, complement component C3, and alpha 1-acid glycoprotein was measured in isolated, perfused liver using [3H]-leucine and a recirculating technique. Urinary excretion of nitrogen and plasma concentration of glucose were higher and plasma total amino acid concentration was lower in hormone-infused than in control rats. Total hepatic protein synthesis in vivo, expressed as the proportion of the protein pool that was replaced each day, was increased from 39% +/- 2% per day to 48% +/- 3% per day (P less than .05) by hormone infusion, but synthesis of secretory proteins in perfused liver was not significantly altered. The results suggest that although total hepatic protein synthesis may be increased by catabolic hormones, other mediator(s) are probably responsible for the stimulation of acute-phase protein synthesis in sepsis.     

High-dose intravenous immunoglobulin modifies complement-mediated in vivo clearance

The mechanism of effect of high-dose intravenous immunoglobulin (IVIG) therapy in immune cytopenias is incompletely known. One of the leading theories ascribes the short-term effects of IVIG to the competition of infused IVIG for Fc receptors, thereby inhibiting IgG-mediated clearance. Using a system independent of IgG-Fc receptor interactions, we examined another potential mechanism of IVIG action. Guinea pigs were infused with a human IVIG preparation at 600 mg/kg/day for two consecutive days. Parallel groups of animals were treated with the same volume and/or concentration of saline and albumin. Clearance of IgM- sensitized guinea pig erythrocytes, which is wholly complement dependent, was significantly retarded in animals treated with high-dose IVIG. The effect was specific for IVIG, since human albumin (as a second foreign protein) failed to change the clearance of IgM- sensitized guinea pig erythrocytes. Experiments in which IVIG-treated animals were subjected to pre- and posttreatment clearance studies revealed heterogeneity among individual animals in respect to their response to IVIG infusions. Decrease of available plasma complement components did not account for the effect, since both C3 and CH50 values remained unchanged after IVIG treatment, despite rising levels of IVIG in sera of treated animals. The results of in vitro C3 uptake studies and the effect of IVIG on clearance of preopsonized cells suggest that IVIG produces a kinetic depression of C3 uptake and modifies the process of complement fragment deposition on erythrocytes. A generalized effect on mononuclear phagocytes is less likely but cannot be wholly ruled out. These studies establish another potential mechanism of IVIG action and suggest extension of its use to other complement-mediated diseases.     

IVIG Adverse Reactions: Potential Role of Cytokines and Vasoactive Substances

Background and Objectives : A clinical study was conducted to determine the effect of IVIG infusion rates on adverse experiences (AE) and on serum levels of cytokines and vasoactive substances. Materials and Methods : Forty-two healthy volunteers were randomized into 3 groups with maximum IVIG infusion rates of 0.04, 0.06, and 0.08 ml/kg/min, and a final dose of 0.5 g IgG/kg body weight. Results : Adverse reactions were noted only at the highest infusion rate of 0.08 ml/kg/min, except in 1 subject infused at 0.06 ml/kg/min. There were significant increases in IL-6 (p = 0.011) and thromboxane B₂ (p = 0.007) in AE subjects as compared to non-AE subjects. Conclusion : IVIG-induced adverse reactions occur more often with rapid infusion rates and may be mediated by elevated levels of inflammatory cytokines and vasoactive substances.     

Prospective study of high-dose intravenous immunoglobulin for the treatment of steroid-resistant polymyositis and dermatomyositis

Abstract

High-dose intravenous immunoglobulin (IVIG) therapy has been effective in treating many autoimmune and systemic inflammatory diseases. In the present prospective study, we evaluated the efficacy of IVIG for patients with polymyositis (PM) and dermatomyositis (DM) refractory to treatment with high-dose corticosteroids. PM/DM was defined as steroid-resistant when the muscle strength of a patient did not improve despite the administration of more than 50?mg prednisolone per day for more than 4 weeks. A total of 12 patients with biopsy-proven, steroid-resistant PM/DM received one infusion of polyethylene glycol-treated human IgG at a dose of 0.4?g per kg per day for five successive days. Three of the patients received a second infusion. All patients were followed for up to 3 months after the infusion. Finally, 8 patients (6 PM and 2 DM; 5 men and 3 women) aged 29–67 years (mean 48 years) were analyzed. Their clinical response was assessed by changes in (a) subjective signs, i.e., fatigue (visual analog scale, VAS), muscle pain (VAS), activities of daily living (ADL), (b) objective signs, i.e., manual muscle strength (MMT) and serum level of creatine kinase (CK). At 12 weeks after the infusion, the patients showed significant improvement in their scores of muscle strength (from a mean of 67.0 to 81.0) and their ADL scores (from a mean of 27.1 to 39.1). The mean serum CK level decreased significantly from 1287.4 to 612.6?IU/l. In addition, the mean VAS of fatigue decreased significantly from 5.5 to 1.3?cm. The physicians’ assessment showed that 87.5% of patients had improved. The average reduced dose of prednisolone was 47.1?mg/day at 12 weeks after infusion in 7 patients who exhibited improvement. Adverse effects, i.e., asymptomatic myocardial infarction and increased blood urea nitrogen (BUN), were noted with two of the 15 infusion (13%). Overall, IVIG was found to be safe and effective for refractory PM and DM.     

Use of high-dose intravenous immunoglobulin in systemic lupus erythematosus: report of three cases

Three patients with life-threatening manifestations of systemic lupus erythematosus (SLE), unresponsive to conventional high-dose corticosteroid and/or immunosuppressive therapy were treated with intravenous polyspecific IgG (IVIG). Following IVIG infusion, lupus encephalitis in the first patient quickly resolved and the impressive improvement of the clinical status was associated with a transient increase in C1q-binding activity. The daily infusion of IgG had to be suspended after three days in the second patient with encephalitis and nephritis, because the renal function rapidly deteriorated; subsequently, six plasma exchanges led to an almost complete recovery. Finally, leukocyte and platelet counts increased and remained within normal range following IgG therapy in the third patient having SLE-associated leuko- and thrombocytopenia. In all three patients a decrease in anti-DNA antibody levels and an increase in total complement hemolytic activity were detected after therapy.     

Prostaglandin E2 affects both insulin secretion and peripheral insulin sensitivity

The effect of prostaglandin E2 (PGE2) on plasma C-peptide (CP) level and peripheral insulin effectiveness was studied in twenty-five healthy volunteers. Plasma CP levels were studied in 14 volunteers (group C) during a three-hours PGE2 infusion. The same experiment was repeated a week later, with saline infusion. Plasma CP level were measured 15 minutes before the infusion, at the beginning of the experiment (0 min) as well as 15, 30, 60, 120 and 180 minutes after the start of the infusion. Peripheral insulin sensitivity was studied in vivo by means of the artificial endocrine pancreas (Biostator), using the euglycaemic hyperinsulinaemic clamp technique. The healthy volunteers underwent a three-hour experiment with saline (group A) or with saline and PGE2-10 micrograms/min during the third hour of clamping (group B). There was a significant decrease in plasma CP level at the 15 th and 30 th minute of PGE2 infusion in the subjects from group C (p less than 0.05). In the group A there was an increase of 14.2% in the amount of glucose infused during the third hour of clamping as compared to the second (2nd-9.673 +/- 1.680 mg/kg/min, 3rd-11.051 +/- 1.802 mg/kg/min). The amount of glucose infused in the subjects of group B remained the same in the course of clamping (2nd hour-7.938 +/- 2.180 mg/kg/min, 3rd hour-7.932 +/- 2.284 mg/kg/min). The difference in the dynamic changes of the amount of glucose infused between the two groups of volunteers (group A and group B) was significant (F = 5.68, p less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)     

Tolerability and Kinetics of a Solvent-Detergent-Treated Intravenous Immunoglobulin Preparation in Hypogammaglobulinaemia Patients

The tolerability and kinetics of a solvent-detergent-treated 6% intravenous immunoglobulin (IVIG) preparation were studied in 15 hypogammaglobulinaemia patients during 3–4 regular substitution infusions of 9–18 g, the mean dose being 359 mg/kg. The infusions were well tolerated, and the trough serum IgG levels achieved were comparable to two commercial IVIG preparations. The stepwise increase of the infusion rate up to 5 mg/kg/min and the use of this IVIG as a 12% solution were possible without serious adverse events in all the 6 studied hypogammaglobulinaemia patients. This greatly reduced the time needed for the infusions.     

Intravenous immunoglobulin preparations induce mild activation of neutrophils in vivo via triggering of macrophages--studies in a rat model

Despite widespread use in various immune disorders, the in vivo mechanisms of action of intravenous immunoglobulin (IVIG) preparations are not well known. We previously reported that human neutrophils degranulate after incubation with IVIG in vitro as a result of interaction with FcgammaRII. The purpose of this study was to determine whether IVIG might stimulate neutrophils in vivo. Anaesthetized rats received a bolus intravenous injection of IVIG preparations, containing either high (aged IVIG) or low (fresh IVIG) amounts or IgG dimers at a dose of 250 mg/kg. Administration of aged IVIG induced neutrophil activation in vivo, whereas no effect was observed after infusion of fresh IVIG. Histological examination of lung tissue demonstrated mild influx of neutrophils into the pulmonary tissue after aged IVIG administration, though gross damage did not occur. Macrophage-depleted rats no longer showed activation of neutrophils after infusion of aged IVIG, suggesting that neutrophils become activated via an indirect macrophage dependent way. We conclude that IVIG induces a mild activation of neutrophils in vivo via triggering of macrophages depending on the amount of IgG dimers. For this reason, IVIG preparations with a high content of dimers may not always be as harmless as generally believed and may be responsible for some of the side-effects observed during IVIG infusions.     

C3 activation products, C3 containing immune complexes, the terminal complement complex and native C9 in patients with rheumatoid arthritis

Complement activation products, C9 and C3-containing circulating immune complexes (CIC), were evaluated in plasma and synovial fluid (SF) from patients with rheumatoid arthritis (RA) and osteoarthritis. C3 activation products and the fluid phase terminal complement complex were considerably elevated in SF from RA patients reaching levels five- to eighttimes that in plasma, consistant with a local activation of the whole cascade in the joints. The results emphazise the importance of detecting C3 activation by neoepitope expression instead of single fragment determinations. The concentration of native C9 was lower in synovial fluid compared with plasma, consistant with the excessive local complement activation. Increased CIC levels which correlated with the degree of complement activation were also found in the SF from the RA patients.     

High doses of immunoglobulin G attenuate immune aggregate-mediated complement activation by enhancing physiologic cleavage of C3b in C3bn- IgG complexes

Intravenously applied human IgG has beneficial effects in treating inflammatory diseases, presumably because it has a complement attenuating role. This role of IgG was studied in vitro by following C3 activation and inactivation in sera that were supplemented with exogenous human IgG and incubated with immune aggregates. IgG added at 2 to 10 mg/mL stimulated the physiologic inactivation of C3b-containing complexes twofold to threefold in 20% sera. This, in turn, lowered the overall C3 activation by 28%, as new C3 convertases primarily assembled on C3b-containing complexes. Exogenous IgG (5 mg/mL) also stimulated inactivation of purified C3b2-IgG complexes, whereby their half-life dropped from 3-4 to 1.5 minutes in 20% serum. IgG appeared to act like a modulator of factor H and I because it did not stimulate inactivation of C3b-containing complexes in factor I-deficient serum. Thus, the known partial protection of C3bn-IgG complexes from inactivation by factor H and I was downregulated by high concentrations of IgG. The ability of high doses of IgG to stimulate complement inactivation is a novel regulatory role of IgG. This may be one of the molecular principles for its therapeutic efficacy in treating complement-mediated inflammations.     

Serum concentrations of immunoglobulins and of antibody isotypes in bone marrow transplant recipients treated with high doses of polyspecific immunoglobulin or with cytomegalovirus hyperimmune globulin.

The kinetics of immunoglobulins (Ig) and antibodies were followed in 10 bone marrow transplant recipients who received either high doses (0.5 g/kg body weight) of polyspecific intravenous Ig (HD-IVIG) weekly or cytomegalovirus hyper-Ig (CMV-IVIG, 0.1 g/kg body weight) every 3 weeks. In the HD-IVIG group, the mean total IgG concentration more than tripled and similar significant increases were seen for IgG1 and IgG2. IgG antibodies to CMV showed a marked increase in the HD-IVIG and a less pronounced rise in the CMV-IVIG group. IgM antibodies to CMV were present initially or became detectable in five patients, unrelated to the IVIG preparation. HD-IVIG induced a significant increase of IgG antibodies to streptococcal group A carbohydrate (A-CHO) and to smooth strain lipopolysaccharides (LPS) but not of antibodies against lipid-A. When the Ig treatment was discontinued, levels of total IgG and of IgG antibody to CMV decreased with an apparent half-life of 30 days. Both IVIG preparations were well tolerated and had no negative feedback on total Ig and on specific antibody production or other antimicrobial defence mechanisms. In patient nos. 4 and 10 who developed severe graft-versus-host-disease, transient serum Ig peaks including several Ig isotypes appeared after day 14. In patient no. 10 this peak contained an IgG antibody to H. influenzae type b (Hib), and IgM antibodies to CMV, Hib, A-CHO and LPS. This study clearly shows that serum concentrations of Ig isotypes, subtypes and specific antibodies, depend on at least four factors: total amount and composition of Ig infused, consumption, catabolism and endogenous production.     

Platelet associated complement components (PAC3c and PAC3d) in patients with autoimmune thrombocytopenia

Platelet associated C3c and C3d (PAC3c and PAC3d) were quantitated by enzyme linked assay in 105 patients with idiopathic autoimmune thrombocytopenia (AITP) in whom elevated platelet associated immunoglobulins (IgG and IgM) had previously been documented. Increased levels of complement components were demonstrated in 46 of 105 patients (43.8%). In 11 of these patients, PAC3d alone was abnormal implying that C3b had been inactivated after cleavage by C3 inactivator in vivo. Complement binding was seen in two of 16 patients (12.5%) with raised PAIgG alone, four of 19 patients (21.0%) with raised PAIgM alone and in 40 of 70 patients (57.1%) in whom PAIgG and PAIgM were raised together. This difference was highly significant (P = 0.01). The clinical implication of these findings are discussed.     

Autologous IgM, IgA, and complement binding to sickle erythrocytes in vivo. Evidence for the existence of dense sickle cell subsets

We have previously reported that sickle erythrocytes sedimenting at high specific density after gradient centrifugation exhibit increased IgG binding in vivo as compared with low-density paired samples. We have performed the present study to determine whether the opsonization of dense sickle cells in vivo could also involve autologous IgM, IgA, and complement. IgA, IgM, and complement binding in vivo to the surface of density-separated sickle erythrocytes was detected by flow cytometric analyses. IgM and complement C3 fragment binding was detected primarily on high-density sickle erythrocytes. With the exception outlined below, IgA binding was detected for all sickle cell fractions that sediment at densities > 1.085 g/mL. IgM, IgA, and complement C3 fragment binding was increased on high-density sickle erythrocytes as compared with low-density paired samples and exceeded that binding to normal erythrocytes by 30% +/- 10% (mean +/- range), 50% +/- 10%, and 41% +/- 5%, respectively. Two-color flow cytometry indicates that high-density sickle cell fractions contain at least two heterogeneous RBC subsets. One is an RBC subset that binds IgA in combination with IgM and C3, and the second subset is devoid of IgA yet binds IgM and C3. These findings indicate that high-density sickle cells exhibit a greater heterogeneity than has been reported in previous studies, which is based on autologous Ig binding in vivo; and suggest that RBC components of this most severely dehydrated sickle cell subpopulation could have heterogeneous origin and pathophysiologic significance. Although the functional role of IgA binding to human RBCs is unclear, our findings that IgM and complement bind to the same high- density sickle cell fractions suggest that both the IgM and the sickle erythrocyte-bound IgG determined in previous studies could mediate the deposition of complement on dense sickle cells in vivo. These findings support the hypotheses that irreversibly sickled cell-enriched high- density sickle RBC subpopulations could be removed from the circulation by erythrocyte phagocytosis that is enhanced by the presence of complement.     

Mononuclear cell complement receptor blockade in primary biliary cirrhosis.

Peripheral blood monocyte and lymphocyte receptors for Fc and C3b fragments were examined in vitro in patients with primary biliary cirrhosis and other chronic liver diseases using sheep red blood cells coated with anti-SRBC IgG1 (to detect Fc receptors) and with anti-SRBC IgM and complement (to detect C3b receptors). The number of C3b receptors detected on 100 monocytes was significantly lower in patients with primary biliary cirrhosis (23.0 +/- 12.0, mean +/- 1 SD) compared with normal controls (57.4 +/- 16.9) and other chronic liver disease (HBsAg negative chronic active hepatitis 62.0 +/- 17.0, alcoholic cirrhosis 50.9 +/- 4.0), while the number of Fc receptors detected on 100 monocytes was not significantly different in all the groups (primary biliary cirrhosis 72.8 +/- 28.6, chronic active hepatitis 74.7 +/- 14.0, alcoholic cirrhosis 58.0 +/- 13.5 and normal controls 69.6 +/- 19.9). When mononuclear cells isolated from normal individuals were pre-incubated with serum from patients with primary biliary cirrhosis before testing their receptor function there was a significant reduction in the number of C3b receptors detected per 100 monocytes (27.6 +/- 10.8) compared with pre-incubation with normal serum (72.0 +/- 18.0). This reduction in C3b-receptor function was again observed when the serum used for pre-incubation was depleted of circulating immune complexes; but when complement was further depleted from these sera, the number of C3b-receptors detected after pre-incubation was similar to normal values (64.0 +/- 11.8). Lymphocyte receptors showed a similar pattern of results. This implies a specific C3b receptor blockade on monocytes and lymphocytes from patients with primary biliary cirrhosis which appears to be because of blocking by serum factor(s) including complement fragments.     

Identification of an Fc gamma receptor-independent mechanism by which intravenous immunoglobulin ameliorates antiphospholipid antibody-induced thrombogenic phenotype

OBJECTIVE: Patients with the antiphospholipid antibody syndrome (APS) often experience recurrent arterial and venous thrombosis and pregnancy losses. Intravenous immunoglobulin (IVIG) therapy has prevented pregnancy loss in some women with APS and has reversed fetal resorption rates in murine models of pregnancy loss. Although the basis for these effects is unknown, effector mechanisms of pathogenic antibodies often involve receptors for IgG (Fc gamma receptors [Fc gammaR]). We examined the potential mechanisms of action of WIG in an in vivo murine model of antiphospholipid antibody (aPL)-induced thrombosis and endothelial cell activation. METHODS: Mice infused with IgG containing human anticardiolipin antibodies (aCL) were treated with IVIG (36 microg i.v.), saline, or ovalbumin. Surgically induced thrombus formation and in vivo leukocyte adhesion to endothelial cells were measured. Circulating levels of aCL were measured by enzyme-linked immunosorbent assay. To determine whether Fc gammaR are required for the effects of IVIG, we treated mice deficient in stimulatory Fc gammaR. To examine the effects of IVIG on endogenously generated antibody, we treated mice immunized with beta2-glycoprotein I (beta2GPI). RESULTS: IVIG treatment inhibited aPL-induced endothelial cell activation and enhancement of thrombosis in mice passively infused with human aPL-containing IgG, and this was associated with a decrease in aPL levels. Similarly, IVIG lowered aPL levels and inhibited thrombogenesis in mice immunized with beta2GPI. The thrombophilic effects of aPL were evident in Fc gammaR-deficient mice. CONCLUSION: Treatment with IVIG inhibits the thrombogenic effects of aPL in vivo and reduces the levels of aCL in the circulation. Blockade of stimulatory Fc gammaR on inflammatory cells is not necessary for this effect. The mechanism of action of IVIG is more likely saturation of the IgG transport receptor, leading to accelerated catabolism of pathogenic aPL. These results have implications in the management of thrombosis in APS and may have applications for pregnant patients with a history of APS.     

Circulating immune complexes in hypertrophic cardiomyopathy and ischemic heart disease]

In 32 patients (pts) with hypertrophic cardiomyopathy (HC), 20 pts with ischaemic heart disease (IHD) and 30 healthy controls, the levels of circulating immune complexes (CIC), immunoglobulins A, G and M, C3c and C4 components of the complement, as well as haemolytic activity of the complement were measured. CIC were assessed using two different methods: a) precipitation with 3% polyethylene glycol with subsequent spectrophotometric measurement of protein content in the precipitate, and b) binding with J-125 labelled staphylococcal +protein ++ A. Pts with HC showed a statistically significant increase in concentration of IgM and the immune complexes (shown with both methods) together with a decrease in C4 and hemolytic activity of the complement. In addition an analysis carried out for each individual patient showed that in some cases an increase in immune complexes concentration was paralleled by a decrease in IgG, C4 and haemolytic activity of the complement. This may suggest that in these pts activation of the complement through the classical pathway can occur. In pts with IHD an increase in immune complexes concentration was demonstrated by precipitation method only. Immune globulines and complement components were within limits for the control group. This suggests that in IHD the complement system is not engaged. Our findings indicate that in HC mechanisms other than those present in myocardial ischaemia must be engaged in inducing changes in the immune system.     

Immunological variables and acute-phase reactants in patients with ankylosing spondylitis (Bechterew's syndrome) and their relatives

Summary Serum and EDTA blood from 120 patients with ankylosing spondylitis (Bechterew's syndrome) and serum from 138 first-degree relatives of patients and from 42 adult blood donors were investigated. Increased serum concentrations of IgA and IgG and complement factors C3 and C4 were found in total groups of HLA B27-positive male or female patients compared with controls or relatives. The men had higher serum concentration of IgA and complement factors than the women, whereas IgM concentration was higher in the women. These patterns were found in controls, in relatives and in patients. Increased concentrations of IgA and of C4 were characteristic of all patients whereas IgG and IgM and C3 concentrations were likewise elevated in patients with peripheral joint arthritis/arthropathy. Increased levels of circulating immune complexes (CIC) were associated with peripheral joint arthritis and were strongly correlated with IgG or CRP concentrations in serum. Total haemolytic complement activity in serum was negatively correlated with concentrations of CIC or CRP indicating complement activation in patients with such complexes. No differences in serum concentrations of Ig or complement factor concentrations were seen between HLA B27-positive and negative relatives with normal sacro-iliac joints or between relatives and controls. Strong mutual correlations were seen among IgG, IgM, complement factors, CRP, SAA, sedimentation rate and alpha₂-macroglobulin. When the present findings were combined with our previous results it turned out that AS, and psoriasis with or without arthropathy, and acute anterior uveitis (AAU) in combination with sacro-iliitis, may be described as IgA-related conditions and that increased serum C4 was related to sacro-iliitis in all these disorders.     

Identification of an Fcγ receptor–independent mechanism by which intravenous immunoglobulin ameliorates antiphospholipid antibody–induced thrombogenic phenotype

Objective

Patients with the antiphospholipid antibody syndrome (APS) often experience recurrent arterial and venous thrombosis and pregnancy losses. Intravenous immunoglobulin (IVIG) therapy has prevented pregnancy loss in some women with APS and has reversed fetal resorption rates in murine models of pregnancy loss. Although the basis for these effects is unknown, effector mechanisms of pathogenic antibodies often involve receptors for IgG (Fcγ receptors [FcγR]). We examined the potential mechanisms of action of IVIG in an in vivo murine model of antiphospholipid antibody (aPL)–induced thrombosis and endothelial cell activation.

Methods

Mice infused with IgG containing human anticardiolipin antibodies (aCL) were treated with IVIG (36 μg IV), saline, or ovalbumin. Surgically induced thrombus formation and in vivo leukocyte adhesion to endothelial cells were measured. Circulating levels of aCL were measured by enzyme‐linked immunosorbent assay. To determine whether FcγR are required for the effects of IVIG, we treated mice deficient in stimulatory FcγR. To examine the effects of IVIG on endogenously generated antibody, we treated mice immunized with β₂‐glycoprotein I (β₂GPI).

Results

IVIG treatment inhibited aPL‐induced endothelial cell activation and enhancement of thrombosis in mice passively infused with human aPL–containing IgG, and this was associated with a decrease in aPL levels. Similarly, IVIG lowered aPL levels and inhibited thrombogenesis in mice immunized with β₂GPI. The thrombophilic effects of aPL were evident in FcγR‐deficient mice.

Conclusion

Treatment with IVIG inhibits the thrombogenic effects of aPL in vivo and reduces the levels of aCL in the circulation. Blockade of stimulatory FcγR on inflammatory cells is not necessary for this effect. The mechanism of action of IVIG is more likely saturation of the IgG transport receptor, leading to accelerated catabolism of pathogenic aPL. These results have implications in the management of thrombosis in APS and may have applications for pregnant patients with a history of APS.