IgM anti-GM2 antibodies in patients with multifocal motor neuropathy target Schwann cells and are associated with early onset.

BACKGROUND: Multifocal motor neuropathy (MMN) is a rare, chronic immune-mediated polyneuropathy characterized by asymmetric distal limb weakness. An important feature of MMN is the presence of IgM antibodies against gangliosides, in particular GM1 and less often GM2. Antibodies against GM1 bind to motor neurons (MNs) and cause damage through complement activation. The involvement of Schwann cells (SCs), expressing GM1 and GM2, in the pathogenesis of MMN is unknown. METHODS: Combining the data of our 2007 and 2015 combined cross-sectional and follow-up studies in Dutch patients with MMN, we evaluated the presence of IgM antibodies against GM1 and GM2 in serum from 124 patients with MMN and investigated their binding to SCs and complement-activating properties. We also assessed the relation of IgM binding and complement deposition with clinical characteristics. RESULTS: Thirteen out of 124 patients (10%) had a positive ELISA titer for IgM anti-GM2. Age at onset of symptoms was significantly lower in MMN patients with anti-GM2 IgM. IgM binding to SCs correlated with IgM anti-GM2 titers. We found no correlation between IgM anti-GM2 titers and MN binding or with IgM anti-GM1 titers. IgM binding to SCs decreased upon pre-incubation of serum with soluble GM2, but not with soluble GM1. IgM anti-GM2 binding to SCs correlated with complement activation, as reflected by increased C3 fixation on SCs and C5a formation in the supernatant. CONCLUSION: Circulating IgM anti-GM2 antibodies define a subgroup of patients with MMN that has an earlier onset of disease. These antibodies probably target SCs specifically and activate complement, similarly as IgM anti-GM1 on MNs. Our data indicate that complement activation by IgM antibodies bound to SCs and MNs underlies MMN pathology.

Cytokine receptor clustering in sensory neurons with an engineered cytokine fusion protein triggers unique pain resolution pathways.

New therapeutic approaches to resolve persistent pain are highly needed. We tested the hypothesis that manipulation of cytokine receptors on sensory neurons by clustering regulatory cytokine receptor pairs with a fusion protein of interleukin (IL)-4 and IL-10 (IL4-10 FP) would redirect signaling pathways to optimally boost pain-resolution pathways. We demonstrate that a population of mouse sensory neurons express both receptors for the regulatory cytokines IL-4 and IL-10. This population increases during persistent inflammatory pain. Triggering these receptors with IL4-10 FP has unheralded biological effects, because it resolves inflammatory pain in both male and female mice. Knockdown of both IL4 and IL10 receptors in sensory neurons in vivo ablated the IL4-10 FP-mediated inhibition of inflammatory pain. Knockdown of either one of the receptors prevented the analgesic gain-of-function of IL4-10 FP. In vitro, IL4-10 FP inhibited inflammatory mediator-induced neuronal sensitization more effectively than the combination of cytokines, confirming its superior activity. The IL4-10 FP, contrary to the combination of IL-4 and IL-10, promoted clustering of IL-4 and IL-10 receptors in sensory neurons, leading to unique signaling, that is exemplified by activation of shifts in the cellular kinome and transcriptome. Interrogation of the potentially involved signal pathways led us to identify JAK1 as a key downstream signaling element that mediates the superior analgesic effects of IL4-10 FP. Thus, IL4-10 FP constitutes an immune-biologic that clusters regulatory cytokine receptors in sensory neurons to transduce unique signaling pathways required for full resolution of persistent inflammatory pain.

ARGX-117, a therapeutic complement inhibiting antibody targeting C2.

BACKGROUND: Activation of the classical and lectin pathway of complement may contribute to tissue damage and organ dysfunction of antibody-mediated diseases and ischemia-reperfusion conditions. Complement factors are being considered as targets for therapeutic intervention. OBJECTIVE: We sought to characterize ARGX-117, a humanized inhibitory monoclonal antibody against complement C2. METHODS: The mode-of-action and binding characteristics of ARGX-117 were investigated in detail. Furthermore, its efficacy was analyzed in in vitro complement cytotoxicity assays. Finally, a pharmacokinetic/pharmacodynamic study was conducted in cynomolgus monkeys. RESULTS: Through binding to the Sushi-2 domain of C2, ARGX-117 prevents the formation of the C3 proconvertase and inhibits classical and lectin pathway activation upstream of C3 activation. As ARGX-117 does not inhibit the alternative pathway, it is expected not to affect the antimicrobial activity of this complement pathway. ARGX-117 prevents complement-mediated cytotoxicity in in vitro models for autoimmune hemolytic anemia and antibody-mediated rejection of organ transplants. ARGX-117 exhibits pH- and calcium-dependent target binding and is Fc-engineered to increase affinity at acidic pH to the neonatal Fc receptor, and to reduce effector functions. In cynomolgus monkeys, ARGX-117 dose-dependently reduces free C2 levels and classical pathway activity. A 2-dose regimen of 80 and 20 mg/kg separated by a week, resulted in profound reduction of classical pathway activity lasting for at least 7 weeks. CONCLUSIONS: ARGX-117 is a promising new complement inhibitor that is uniquely positioned to target both the classical and lectin pathways while leaving the alternative pathway intact.

A mutation in the kringle domain of human factor XII that causes autoinflammation, disturbs zymogen quiescence, and accelerates activation.

Coagulation factor XII (FXII) drives production of the inflammatory peptide bradykinin. Pathological mutations in the F12 gene, which encodes FXII, provoke acute tissue swelling in hereditary angioedema (HAE). Interestingly, a recently identified F12 mutation, causing a W268R substitution, is not associated with HAE. Instead, FXII-W268R carriers experience cold-inducible urticarial rash, arthralgia, fever, and fatigue. Here, we aimed to investigate the molecular characteristics of the FXII-W268R variant. We expressed wild type FXII (FXII-WT), FXII-W268R, and FXII-T309R (which causes HAE), as well as other FXII variants in HEK293 freestyle cells. Using chromogenic substrate assays, immunoblotting, and ELISA, we analyzed expression media, cell lysates, and purified proteins for FXII activation. Recombinant FXII-W268R forms increased amounts of intracellular cleavage products that are also present in expression medium and display enzymatic activity. The active site-incapacitated variant FXII-W268R/S544A reveals that intracellular fragmentation is largely dependent on autoactivation. Purified FXII-W268R is highly sensitive to activation by plasma kallikrein and plasmin, compared with FXII-WT or FXII-T309R. Furthermore, binding studies indicated that the FXII-W268R variant leads to the exposure of a plasminogen-binding site that is cryptic in FXII-WT. In plasma, recombinant FXII-W268R spontaneously triggers high-molecular-weight kininogen cleavage. Our findings suggest that the W268R substitution influences FXII protein conformation and exposure of the activation loop, which is concealed in FXII-WT. This results in intracellular autoactivation and constitutive low-grade secretion of activated FXII. These findings help to explain the chronically increased contact activation in carriers of the FXII-W268R variant.

Evidence for bradykinin release in chronic spontaneous urticaria.

BACKGROUND: Chronic spontaneous urticaria (CSU) is characterized by recurrent itchy weals and/or angioedema and is believed to be driven by mast cell activation. It was shown that excessive mast cell activation during anaphylaxis initiates contact activation, resulting in bradykinin release. Evidence for bradykinin release was never demonstrated in CSU. OBJECTIVE: To study biomarkers of bradykinin release in CSU. METHODS: Plasma samples of CSU patients were collected during routine visits at the outpatient clinic. Cleaved high molecular weight kininogen (cHK) was used as a biomarker for bradykinin release. cHK, factor XIIa-C1-inhibitor (FXIIa-C1-INH), kallikrein-C1-INH, plasmin-antiplasmin (PAP) complexes and soluble urokinase-type plasminogen activator receptor (suPAR) levels were determined by ELISA. Clinical data and data on tryptase levels were collected from medical records. cHK levels were compared to previously determined levels in hereditary angioedema (HAE). RESULTS: One hundred seventeen samples from 88 CSU patients and 28 samples from healthy controls were analysed. Median cHK level in CSU was 9.1% (range: 1.4%-21.5%), significantly increased compared to healthy controls (median 6.0% range: 0%-19.9%; P = .0005) and comparable to HAE (n = 46, median 10.3%, range 0%-44.3%, P > .9999). cHK levels normalized in patients during disease remission (median 6.5% range 1.5%-20.8%) but were not dependent on the presence of angioedema, acute angioedema attacks or response to antihistamines. Surprisingly, cHK levels were inversely correlated to serum tryptase (r = -0.65 P = .0137). C1-INH complexes and suPAR levels were not elevated in patients compared to healthy controls. PAP-complex levels in patients were elevated compared to healthy controls but there was no correlation between PAP-complex and cHK levels. CONCLUSIONS: cHK levels are elevated in symptomatic CSU patients compared to healthy controls, indicating increased bradykinin production. Increased cHK levels are not limited to patients with angioedema. CLINICAL RELEVANCE: If elevated bradykinin generation has clinical implications in the pathology of CSU is open to debate.

Increased intra-articular granzyme M may trigger local IFN-λ1/IL-29 response in rheumatoid arthritis.

OBJECTIVES: Granzymes are serine proteases involved in eliminating tumour cells and virally infected cells. In addition, extracellular granzyme levels are elevated in inflammatory conditions, including several types of infection and autoimmune diseases, such as rheumatoid arthritis (RA). While GrA and GrB have been associated with RA, a role for the other three granzymes (GrH, GrK, and GrM) in this disease remains unclear. Here, we aimed to investigate the presence and role of GrM and GrK in serum and synovial fluid of patients with RA, psoriatic arthritis, and osteoarthritis. METHODS: Granzyme levels were determined in serum, synovial fluid, peripheral blood mononuclear cells (PBMCs) and synovial fluid mononuclear cells (SFMCs) of RA patients and relevant control groups. In addition, the link between GrM and inflammatory cytokines in synovial fluid was investigated. RESULTS: Serum GrM and GrK levels were not affected in RA. GrM, but not GrK, levels were elevated in synovial fluid of RA patients. GrM was mainly expressed by cytotoxic lymphocytes in SFMCs with a similar expression pattern as compared with PBMCs. Intra-articular GrM expression correlated with IL-25, IL-29, XCL1, and TNFα levels. Intriguingly, purified GrM triggered the release of IL-29 (IFN-λ1) from human fibroblasts in vitro. CONCLUSIONS: These data indicate that GrM levels are increased in RA synovial fluid and that GrM can stimulate proinflammatory IL-29 release from fibroblasts, suggesting a role of GrM in the pathogenesis of RA.

Sialic Acid-Engineered IL4-10 Fusion Protein is Bioactive and Rapidly Cleared from the Circulation.

PURPOSE: Modulating sialylation of therapeutic glycoproteins may be used to influence their clearance and systemic exposure. We studied the effect of low and high sialylated IL4-10 fusion protein (IL4-10 FP) on in vitro and in vivo bioactivity and evaluated the effect of differential sialylation on pharmacokinetic parameters. METHODS: CHO cell lines producing low (IL4-10 FP lowSA) and high sialylated (IL4-10 FP highSA) fusion protein were generated. Bioactivity of the proteins was evaluated in an LPS-stimulated whole blood assay. Pharmacokinetics were studied in rats, analyzing plasma levels of IL4-10 FP upon intravenous injection. In vivo activity was assessed in an inflammatory pain mice model upon intrathecal injection. RESULTS: IL4-10 FP lowSA and IL4-10 FP highSA had similar potency in vitro. The pharmacokinetics study showed a 4-fold higher initial systemic clearance of IL4-10 FP lowSA, whereas the calculated half-life of both IL4-10 FP lowSA and IL4-10 FP highSA was 20.7 min. Finally, both IL4-10 FP glycoforms inhibited persistent inflammatory pain in mice to the same extent. CONCLUSIONS: Differential sialylation of IL4-10 fusion protein does not affect the in vitro and in vivo activity, but clearly results in a difference in systemic exposure. The rapid systemic clearance of low sialylated IL4-10 FP could be a favorable characteristic to minimize systemic exposure after administration in a local compartment.

Simultaneous Quantification of Free Adalimumab and Infliximab in Human Plasma Using a Target-Based Sample Purification and Liquid Chromatography-Tandem Mass Spectrometry.

BACKGROUND: Therapeutic drug monitoring of tumor necrosis factor alpha (TNF-α) inhibitors such as adalimumab (ADM) and infliximab (IFX) is considered of added value for patients with systemic inflammatory diseases. In contrast to enzyme-linked immunosorbent assay methods, liquid chromatography-tandem mass spectrometry methods allow for simultaneous quantification of multiple target antibodies in 1 run and thus providing a higher sample throughput. We describe a fast sample work-up strategy for the absolute and simultaneous quantification of ADM and IFX therapeutic monoclonal antibodies in human plasma samples using a target-specific sample purification in combination with liquid chromatography-tandem mass spectrometry. METHODS: The sample purification was based on the selective capture of ADM and IFX in human plasma or serum using biotinylated TNF-α (b-TNF-α), which was coated on a streptavidin 96-well plate. After elution, analytes were heat denatured and trypsin digested to obtain signature peptides for quantification. Stable isotopically labeled ADM and IFX were introduced as internal standard before sample purification. RESULTS: The method was successfully validated following current European medicines agency guidelines. The linear dynamic rage for both analytes were 1-32 mcg/mL with an excellent mean coefficient of determination, R = 0.9994 for ADM and 0.9996 for IFX. Within-run and between-run imprecision and accuracy were within acceptance criteria. Cross-validation against enzyme-linked immunosorbent assay method showed a high between-method correlation R = 0.962 for ADM and R = 0.982 for IFX. CONCLUSIONS: This method provides an easy, efficient, and cost-effective workflow for therapeutic drug monitoring patients treated with ADM or IFX.

Quantification of total dinutuximab concentrations in neuroblastoma patients with liquid chromatography tandem mass spectrometry.

Neuroblastoma is one of the most commonly found solid tumors in children. The monoclonal antibody dinutuximab (DNX) targets the sialic acid-containing glycosphingolipid GD2 expressed on almost all neuroblastoma tumor cells and induces cell lysis. However, the expression of GD2 is not limited to tumor cells only, but is also present on central nerve tissue and peripheral nerve cells explaining dinutuximab toxicity. The most common adverse reactions are pain and discomfort, which may lead to discontinuation of the treatment. Furthermore, there is little to no data available on exposure and effect relationships of dinutuximab. We, therefore, developed an easy method in order to quantify dinutuximab levels in human plasma. Ammonium sulfate (AS) was used to precipitate all immunoglobulins (IgGs) in human plasma. After centrifugation, supernatant containing albumin was decanted and the precipitated IgG fraction was re-dissolved in a buffer containing 0.5% sodium dodecyl sulfate (SDS). Samples were then reduced, alkylated, and digested with trypsin. Finally, a signature peptide in complementarity determining region 1 of DNX heavy chain was quantified on LC-MS/MS using a stable isotopically labeled peptide as internal standard. AS purification efficiently removed 97.5% of the albumin fraction in the supernatant layer. The validation performed on DNX showed that within-run and between-run coefficients of variation (CV) for lower limit of quantification (LLOQ) were 5.5 and 1.4%, respectively. The overall CVs for quality control (QC) low, QC med, and QC high levels were < 5%. Linearity in the range 1-32 mg/L was excellent (r2 > 0.999). Selectivity, stability, and matrix effect were in concordance with EMA guidelines. In conclusion, a method to quantify DNX in human plasma was successfully developed. In addition, the high and robust process efficiency enabled the utilization of a stable isotopically labeled (SIL) peptide instead of SIL DNX, which was commercially unavailable. Graphical abstract.

Effect of cytomegalovirus reactivation on the time course of systemic host response biomarkers in previously immunocompetent critically ill patients with sepsis: a matched cohort study.

BACKGROUND: Cytomegalovirus (CMV) reactivation in previously immunocompetent critically ill patients is associated with increased mortality, which has been hypothesized to result from virus-induced immunomodulation. Therefore, we studied the effects of CMV reactivation on the temporal course of host response biomarkers in patients with sepsis. METHODS: In this matched cohort study, each sepsis patient developing CMV reactivation between day 3 and 17 (CMV+) was compared with one CMV seropositive patient without reactivation (CMVs+) and one CMV seronegative patient (CMVs-). CMV serostatus and plasma loads were determined by enzyme-linked immunoassays and real-time polymerase chain reaction, respectively. Systemic interleukin-6 (IL-6), IL-8, IL-18, interferon-gamma-induced protein-10 (IP-10), neutrophilic elastase, IL-1 receptor antagonist (RA), and IL-10 were measured at five time points by multiplex immunoassay. The effects of CMV reactivation on sequential concentrations of these biomarkers were assessed in multivariable mixed models. RESULTS: Among 64 CMV+ patients, 45 could be matched to CMVs+ or CMVs- controls or both. The two baseline characteristics and host response biomarker levels at viremia onset were similar between groups. CMV+ patients had increased IP-10 on day 7 after viremia onset (symmetric percentage difference +44% versus -15% when compared with CMVs+ and +37% versus +4% when compared with CMVs-) and decreased IL-1RA (-41% versus 0% and -49% versus +10%, respectively). However, multivariable analyses did not show an independent association between CMV reactivation and time trends of IL-6, IP-10, IL-10, or IL-1RA. CONCLUSION: CMV reactivation was not independently associated with changes in the temporal trends of host response biomarkers in comparison with non-reactivating patients. Therefore, these markers should not be used as surrogate clinical endpoints for interventional studies evaluating anti-CMV therapy.

CD8+ T Cells and Endogenous IL-10 Are Required for Resolution of Chemotherapy-Induced Neuropathic Pain.

Chemotherapy-induced peripheral neuropathy (CIPN), characterized by pain and numbness in hands and feet, is a common side effect of cancer treatment. In most patients, symptoms of CIPN subside after treatment completion. However, in a substantial subgroup, CIPN persists long into survivorship. Impairment in pain resolution pathways may explain persistent CIPN. We investigated the contribution of T cells and endogenous interleukin (IL)-10 to resolution of CIPN. Paclitaxel-induced mechanical allodynia was prolonged in T-cell-deficient (Rag1-/-) mice compared with wild-type (WT) mice. There were no differences between WT and Rag1-/- mice in severity of paclitaxel-induced mechanical allodynia. Adoptive transfer of either CD3+ or CD8+, but not CD4+, T cells to Rag1-/- mice normalized resolution of CIPN. Paclitaxel treatment increased the number of T cells in lumbar dorsal root ganglia (DRG), where CD8+ T cells were the major subset. Inhibition of endogenous IL-10 signaling by intrathecal injection of anti-IL-10 to WT mice or Rag1-/- mice reconstituted with CD8+ T cells delayed recovery from paclitaxel-induced mechanical allodynia. Recovery was also delayed in IL-10 knock-out mice. Conversely, administration of exogenous IL-10 attenuated paclitaxel-induced allodynia. In vitro, IL-10 suppressed abnormal paclitaxel-induced spontaneous discharges in DRG neurons. Paclitaxel increased DRG IL-10 receptor expression and this effect requires CD8+ T cells. In conclusion, we identified a novel mechanism for resolution of CIPN that requires CD8+ T cells and endogenous IL-10. We propose that CD8+ T cells increase DRG IL-10 receptor expression and that IL-10 suppresses the abnormal paclitaxel-induced spontaneous discharges by DRG neurons to promote recovery from CIPN. SIGNIFICANCE STATEMENT: Chemotherapy-induced peripheral neuropathy persists after completion of cancer treatment in a significant subset of patients, whereas others recover. Persistent neuropathy after completion of cancer treatment severely affects quality of life. We propose that understanding how neuropathy resolves will identify novel avenues for treatment. We identified a novel and critical role for CD8+ T cells and for endogenous IL-10 in recovery from paclitaxel-induced neuropathy in mice. Enhancing the capacity of CD8+ T cells to promote resolution or increasing IL-10 signaling are promising targets for novel interventions. Clinically, peripheral blood CD8+ T-cell function and/or the capacity of individuals to produce IL-10 may represent biomarkers of risk for developing persistent peripheral neuropathy after completion of cancer treatment.

Granzymes regulate proinflammatory cytokine responses.

Granzymes (Grs) are serine proteases mainly produced by cytotoxic lymphocytes and are traditionally considered to cause apoptosis in tumor cells and virally infected cells. However, the cytotoxicity of several Grs is currently being debated, and additional, predominantly extracellular, functions of Grs in inflammation are emerging. Extracellular soluble Grs are elevated in the circulation of patients with autoimmune diseases and infections. Additionally, Grs are expressed by several types of immune cells other than cytotoxic lymphocytes. Recent research has revealed novel immunomodulatory functions of Grs. In this review, we provide a comprehensive overview on the role of Grs in inflammation, highlighting their role in cytokine induction and processing.

Granzyme K synergistically potentiates LPS-induced cytokine responses in human monocytes.

Granzymes are serine proteases released by cytotoxic lymphocytes to induce apoptosis in virus-infected cells and tumor cells. Evidence is emerging that granzymes also play a role in controlling inflammation. Granzyme serum levels are elevated in patients with autoimmune diseases and infections, including sepsis. However, the function of extracellular granzymes in inflammation largely remains unknown. Here, we show that granzyme K (GrK) binds to Gram-negative bacteria and their cell-wall component lipopolysaccharide (LPS). GrK synergistically enhances LPS-induced cytokine release in vitro from primary human monocytes and in vivo in a mouse model of LPS challenge. Intriguingly, these extracellular effects are independent of GrK catalytic activity. GrK disaggregates LPS from micelles and augments LPS-CD14 complex formation, thereby likely boosting monocyte activation by LPS. We conclude that extracellular GrK is an unexpected direct modulator of LPS-TLR4 signaling during the antimicrobial innate immune response.

Angioedema attacks in patients with hereditary angioedema: Local manifestations of a systemic activation process.

Hereditary angioedema (HAE) caused by a deficiency of functional C1-inhibitor (C1INH) becomes clinically manifest as attacks of angioedema. C1INH is the main inhibitor of the contact system. Poor control of a local activation process of this system at the site of the attack is believed to lead to the formation of bradykinin (BK), which increases local vasopermeability and mediates angioedema on interaction with BK receptor 2 on the endothelium. However, several observations in patients with HAE are difficult to explain from a pathogenic model claiming a local activation process at the site of the angioedema attack. Therefore we postulate an alternative model for angioedema attacks in patients with HAE, which assumes a systemic, fluid-phase activation of the contact system to generate BK and its breakdown products. Interaction of these peptides with endothelial receptors that are locally expressed in the affected tissues rather than with receptors constitutively expressed by the endothelium throughout the whole body explains that such a systemic activation process results in local manifestations of an attack. In particular, BK receptor 1, which is induced on the endothelium by inflammatory stimuli, such as kinins and cytokines, meets the specifications of the involved receptor. The pathogenic model discussed here also provides an explanation for why angioedema can occur at multiple sites during an attack and why HAE attacks respond well to modest increases of circulating C1INH activity levels because inhibition of fluid-phase Factor XIIa and kallikrein requires lower C1INH levels than inhibition of activator-bound factors.

Allergenicity and safety of recombinant human C1 esterase inhibitor in patients with allergy to rabbit or cow's milk.

BACKGROUND: Recombinant human C1 inhibitor (rhC1INH) for on-demand treatment of hereditary angioedema is purified from milk of transgenic rabbits. It contains low amounts (<0.002%) of host-related impurities, which could trigger hypersensitivity reactions in patients with rabbit allergy (RA) and/or cow's milk allergy (CMA). OBJECTIVE: This study is an assessment of allergenicity and safety of rhC1INH in patients with RA and/or CMA. METHODS: Patients with CMA and/or RA underwent skin prick test (SPT), intracutaneous test (ICT), and, when results for both were negative, subcutaneous (SC) challenge with up to 2100U (14 mL) rhC1INH. The negative predictive value of the skin test protocol was calculated, defined as the ratio of patients without systemic symptoms of hypersensitivity following SC challenge, over the number of patients having tested negative for both the SPT and the ICT. Adverse events after exposure to rhC1INH were recorded. RESULTS: Twenty-six patients with RA and/or CMA were enrolled. Twenty-four had negative SPT and ICT results for rhC1INH, whereas 2 had negative SPT result but positive ICT result to rhC1INH (only the highest concentration). Twenty-two patients with negative SPT and ICT results underwent SC challenge. None developed allergic symptoms. Local treatment-emergent adverse events occurred in 7 patients (32%) after SC challenge. In 5 these were considered drug related. All were mild. CONCLUSIONS: None of the patients with negative SPT and ICT results for rhC1INH had allergic symptoms during rhC1INH challenge. The negative predictive value of the combination of SPT and ICT for the outcome of the SC challenge was 100% (95% CI, 84.6%-100%). SC administration of rhC1INH was well tolerated.

IgG antibodies in food allergy influence allergen-antibody complex formation and binding to B cells: a role for complement receptors.

Allergen-IgE complexes are more efficiently internalized and presented by B cells than allergens alone. It has been suggested that IgG Abs induced by immunotherapy inhibit these processes. Food-allergic patients have high allergen-specific IgG levels. However, the role of these Abs in complex formation and binding to B cells is unknown. To investigate this, we incubated sera of peanut- or cow's milk-allergic patients with their major allergens to form complexes and added them to EBV-transformed or peripheral blood B cells (PBBCs). Samples of birch pollen-allergic patients were used as control. Complex binding to B cells in presence or absence of blocking Abs to CD23, CD32, complement receptor 1 (CR1, CD35), and/or CR2 (CD21) was determined by flow cytometry. Furthermore, intact and IgG-depleted sera were compared. These experiments showed that allergen-Ab complexes formed in birch pollen, as well as food allergy, contained IgE, IgG1, and IgG4 Abs and bound to B cells. Binding of these complexes to EBV-transformed B cells was completely mediated by CD23, whereas binding to PBBCs was dependent on both CD23 and CR2. This reflected differential receptor expression. Upon IgG depletion, allergen-Ab complexes bound to PBBCs exclusively via CD23. These data indicated that IgG Abs are involved in complex formation. The presence of IgG in allergen-IgE complexes results in binding to B cells via CR2 in addition to CD23. The binding to both CR2 and CD23 may affect Ag processing and presentation, and (may) thereby influence the allergic response.

Population pharmacokinetics of recombinant human C1 inhibitor in patients with hereditary angioedema.

AIMS: To characterize the pharmacokinetics (PK) of recombinant human C1 inhibitor (rhC1INH) in healthy volunteers and hereditary angioedema (HAE) patients. METHODS: Plasma levels of C1INH following 294 administrations of rhC1INH in 133 subjects were fitted using nonlinear mixed-effects modelling. The model was used to simulate maximal C1INH levels for the proposed dosing scheme. RESULTS: A one-compartment model with Michaelis-Menten elimination kinetics described the data. Baseline C1INH levels were 0.901 [95% confidence interval (CI): 0.839-0.968] and 0.176 U ml(-1) (95% CI: 0.154-0.200) in healthy volunteers and HAE patients, respectively. The volume of distribution of rhC1INH was 2.86 l (95% CI: 2.68-3.03). The maximal rate of elimination and the concentration corresponding to half this maximal rate were 1.63 U ml(-1) h(-1) (95% CI: 1.41-1.88) and 1.60 U ml(-1) (95% CI: 1.14-2.24), respectively, for healthy volunteers and symptomatic HAE patients. The maximal elimination rate was 36% lower in asymptomatic HAE patients. Peak C1INH levels did not change upon repeated administration of rhC1INH. Bodyweight was found to be an important predictor of the volume of distribution. Simulations of the proposed dosing scheme predicted peak C1INH concentrations above the lower level of the normal range (0.7 U ml(-1)) for at least 94% of all patients. CONCLUSIONS: The population PK model for C1INH supports a dosing scheme on a 50 U kg(-1) basis up to 84 kg, with a fixed dose of 4200 U above 84 kg. The PK of rhC1INH following repeat administration are consistent with the PK following the first administration.