A high-affinity natural autoantibody from human cord blood defines a physiologically relevant epitope on the FcepsilonRIalpha.

Natural Abs represent the indigenous immune repertoire and are thus present at birth and persist throughout life. Previously, human autoantibodies to the alpha domain of the high-affinity IgE receptor (FcepsilonRIalpha) have been isolated from Ab libraries derived from normal donors and patients with chronic urticaria. To investigate whether these anti-FcepsilonRIalpha Abs are present in the germline repertoire, we constructed a phage Fab display library from human cord blood, which represents the naive immune repertoire before exposure to exogenous Ags. All isolated clones specific to the FcepsilonRIalpha had the same sequence. This single IgM Ab, named CBMalpha8, was strictly in germline configuration and had high affinity and functional in vitro anaphylactogenic activity. Inhibition experiments indicated an overlapping epitope on the FcepsilonRIalpha recognized by both CBMalpha8 and the previously isolated anti-FcepsilonRIalpha Abs from autoimmune and healthy donors. This common epitope on FcepsilonRIalpha coincides with the binding site for IgE. Affinity measurements demonstrated the presence of Abs showing CBMalpha8-like specificity, but with a significantly lower affinity in i.v. Ig, a therapeutic multidonor IgG preparation. We propose a hypothesis of escape mutants, whereby the resulting lower affinity IgG anti-FcepsilonRIalpha Abs are rendered less likely to compete with IgE for binding to FcepsilonRIalpha.

The protease inhibitor alpha-2-macroglobulin-like-1 is the p170 antigen recognized by paraneoplastic pemphigus autoantibodies in human

Paraneoplastic pemphigus (PNP) is a devastating autoimmune blistering disease, involving mucocutaneous and internal organs, and associated with underlying neoplasms. PNP is characterized by the production of autoantibodies targeting proteins of the plakin and cadherin families involved in maintenance of cell architecture and tissue cohesion. Nevertheless, the identity of an antigen of Mr 170,000 (p170), thought to be critical in PNP pathogenesis, has remained unknown.

Naturally occurring antibodies/autoantibodies in polyclonal immunoglobulin concentrates

It was a long way from the use of hyperimmune animal sera for the treatment of toxin-producing infections to the production of polyclonal, polyspecific human immunoglobulin preparations and the use of NAbs as therapeutic tools for autoimmune and inflammatory diseases. Some highlights of the development of knowledge in blood fractionation techniques, basic science and clinical wisdom are reviewed in this chapter. Proudly we mention the outstanding contribution of Swiss scientists and clinicians in the development of IVIG as clinical tool for some otherwise untreatable diseases or taking advantage of its low adverse event profile in long-term treatment of other chronic autoimmune and inflammatory diseases. This chapter summarizes some of the characteristics and the effects in humans of NAbs which are present in IgG concentrates. We call attention to the fact that the human data remain, at least in part, incomplete, among others because even with the most efficient large-scale techniques available not more than approximately 50% of the total IgG in plasma can be fractionated into an immunoglobulin G concentrate.

Immunologic and functional evidence for anti-Siglec-9 autoantibodies in intravenous immunoglobulin preparations

Human intravenous immunoglobulin (IVIg) preparations are increasingly used for the treatment of autoimmune diseases. Earlier work demonstrated the presence of autoantibodies against Fas in IVIg, suggesting that IVIg might be able to induce caspase-dependent cell death in Fas-sensitive cells. In this study, we demonstrate that sialic acid-binding Ig-like lectin 9 (Siglec) represents a surface molecule on neutrophils that is activated by IVIg, resulting in caspase-dependent and caspase-independent forms of cell death. Neutrophil death was mediated by naturally occurring anti-Siglec-9 autoantibodies present in IVIg. Moreover, the efficacy of IVIg-mediated neutrophil killing was enhanced by the proinflammatory cytokines granulocyte/macrophage colony-stimulating factor (GM-CSF) and interferon-gamma (IFN-gamma), and this additional cell death required reactive oxygen species (ROSs) but not caspases. Anti- Siglec-9 autoantibody-depleted IVIg failed to induce this caspase-independent neutrophil death. These findings contribute to our understanding of how IVIg preparations exert their immunoregulatory effects under pathologic conditions and may provide a possible explanation for the neutropenia that is sometimes seen in association with IVIg therapy.

Intravenous immunoglobulin preparations contain anti-Siglec-8 autoantibodies

BACKGROUND: Human intravenous immunoglobulin (IVIg) preparations are used for the treatment of autoimmune and allergic diseases. Natural autoantibodies are believed to contribute to IVIg-mediated anti-inflammatory effects. OBJECTIVE: To address the question of whether IVIg preparations contain anti-sialic acid-binding Ig-like lectin-8 (anti-Siglec-8) autoantibodies. METHODS: The presence of possible anti-Siglec-8 autoantibodies in IVIg preparations was first examined by functional eosinophil death and apoptosis assays. Specificity of IVIg effects was shown by depleting anti-Siglec-8 autoantibodies from IVIg. Binding of purified anti-Siglec-8 autoantibodies to recombinant Siglec-8 was demonstrated by an immunodot assay. RESULTS: IVIg exerts cytotoxic effects on purified human blood eosinophils. Both potency and efficacy of the IVIg-mediated eosinophil killing effect was enhanced by IL-5, granulocyte/macrophage colony-stimulating factor, IFN-gamma, TNF-alpha, and leptin. Similarly, inflammatory eosinophils obtained from patients suffering from the hypereosinophilic syndrome (HES) demonstrated increased Siglec-8 cytotoxic responses when compared with normal blood eosinophils. Pharmacologic blocking experiments indicated that the IVIg-mediated additional eosinophil death in the presence of cytokines is largely caspase-independent, but it depends on reactive oxygen species. Anti-Siglec-8 autoantibody-depleted IVIg failed to induce caspase-independent eosinophil death. CONCLUSION: IVIg preparations contain natural anti-Siglec-8 autoantibodies. CLINICAL IMPLICATIONS: Anti-Siglec-8 autoantibodies present in IVIg preparations may have therapeutic relevance in autoimmune and allergic diseases, respectively, such as Churg-Strauss syndrome.

Autophagic-like cell death in neutrophils induced by autoantibodies

Human neutrophils undergo autophagic-like cell death following Sialic acid binding immunoglobulin-like lectin-9 (Siglec-9) ligation and concurrent stimulation with certain, but not all, neutrophil survival cytokines. Caspase inhibition by these cytokines is required, but is not sufficient, to trigger this particular form of cell death. Additional mechanisms may involve reactive oxygen species (ROS), and blocking of ROS or prevention of ROS production prevents autophagic-like neutrophil death. Interestingly, human intravenous immunoglobulin (IVIg) preparations contain natural anti-Siglec-9 autoantibodies, which are able to ligate Siglec-9 on neutrophils and induce autophagic-like cell death in the presence of granulocyte-macrophage colony-stimulating factor (GM-CSF) and some other survival cytokines. Here, we discuss the pathophysiological and therapeutic implications of these recent findings.

Natural anti-Siglec autoantibodies mediate potential immunoregulatory mechanisms: implications for the clinical use of intravenous immunoglobulins (IVIg)

Human intravenous immunoglobulins (IVIg) contain natural autoantibodies against the inhibitory lectin-receptors Siglec-8 and Siglec-9. These two members of the Siglec family are known to mediate both inhibitory and death signals. Here, we discuss recent findings regarding the cytotoxic effects of natural anti-Siglec autoantibodies on both neutrophils and eosinophils, and present the concept of a novel regulatory mechanism exhibiting anti-inflammatory properties. Consequently, IVIg may amplify this regulatory pathway by increasing the concentration of natural anti-Siglec autoantibodies in blood and tissues.

Sensitization to wasp venom does not induce autoantibodies leading to infertility

Antigenic cross-reactivity has been described between the venom allergen (antigen 5) and mammalian testis proteins. Based on an allergen database we have previously shown that allergens can be represented by allergen motifs. A motif group was found containing venom antigen 5 sequences from different vespids. Using an optimized amino acid profile based on antigen 5 sequences for searching cross-reactive proteins, three human semen proteins belonging to the family of cysteine-rich secretory proteins (hCRISP) were found in the Swiss Protein database. To analyze antigenic cross-reactivity between antigen 5 and hCRISPs, antigen 5 from yellow jacket venom (Ves v 5) and two hCRISPs (CRISP-2 and -3) were chosen and produced as recombinant proteins in E. coli. A correlation was found between antibodies reacting with rVes v 5 and rhCRISP-2, -3 in a small human sera population indicating the presence of cross-reactive antibodies in human serum. Using intravenous immunoglobulin (IVIg), a therapeutic multidonor IgG preparation, cross-reactive antibodies were isolated that recognize rVes v 5, hCRISP-2 and -3 suggesting the presence of common epitopes between Ves v 5 and hCRISPs. However this cross-reactivity seems not to be linked to allergy to wasp venom as we could show no correlation between increasing CAP-class IgE level to wasp venom and IgG to sperm extract and hCRISPs. These data suggest that higher sensitization to wasp venom does not induce more antibodies against autoantigens and might not represent a higher risk to develop autoantibodies leading to infertility.

Anti-Alpha-2-Macroglobulin-Like-1 Autoantibodies Are Detected Frequently and May Be Pathogenic in Paraneoplastic Pemphigus

Paraneoplastic pemphigus (PNP) shows autoantibodies mainly to plakin and desmosomal cadherin family proteins. We have recently identified alpha-2-macroglobulin-like-1 (A2ML1), a broad range protease inhibitor, as a unique PNP antigen. In this study, we tested a large number of PNP sera by various methods. Forty (69.0%) of 58 PNP sera recognized A2ML1 recombinant protein expressed in COS7 cells by immunofluorescence (IF) and/or immunoprecipitation (IP)/immunoblotting (IB). IP/IB showed higher sensitivity than IF. In addition, 22 (37.9%) PNP sera reacted with A2ML1 by IB of cultured normal human keratinocytes (NHKs) under non-reducing conditions. Statistical analyses using various clinical and immunological data showed that the presence of anti-A2ML1 autoantibodies was associated with early disease onset and absence of ocular lesions. Next, to investigate the pathogenic role of anti-A2ML1 antibody, we performed additional functional studies. Addition of anti-A2ML1 polyclonal antibody to culture media decreased NHK cell adhesion examined by dissociation assay, and increased plasmin activity detected by casein zymography, suggesting that anti-A2ML1 antibody may decrease NHK cell adhesion through plasmin activation by inhibition of A2ML1. This study demonstrates that autoantibodies to A2ML1 are frequently and specifically detected and may have a pathogenic role in PNP.

Microbiota Promotes Chronic Pulmonary Inflammation by Enhancing IL-17A and Autoantibodies

RATIONALE Changes in the pulmonary microbiota are associated with progressive respiratory diseases including chronic obstructive pulmonary disease. Whether there is a causal relationship between these changes and disease progression remains unknown. OBJECTIVE To investigate the link between an altered microbiota and disease, we utilized a model of chronic lung inflammation in specific pathogen free (SPF) mice and mice depleted of microbiota by antibiotic treatment or devoid of a microbiota (axenic). METHODS Mice were challenged with LPS/elastase intranasally over 4 weeks, resulting in a chronically inflamed and damaged lung. The ensuing cellular infiltration, histological damage and decline in lung function were quantified. MEASUREMENTS AND MAIN RESULTS Similar to human disease, the composition of the pulmonary microbiota was altered in disease animals. We found that the microbiota richness and diversity were decreased in LPS/Elastase-treated mice, with an increased representation of the genera Pseudomonas, Lactobacillus and a reduction in Prevotella. Moreover, the microbiota was implicated in disease development as mice depleted of microbiota exhibited an improvement in lung function, reduction in airway inflammation, decrease in lymphoid neogenesis and auto-reactive antibody responses. The absence of microbial cues also markedly decreased the production of IL-17A, whilst intranasal transfer of fluid enriched with the pulmonary microbiota isolated from diseased mice enhanced IL-17A production in the lungs of antibiotic treated or axenic recipients. Finally, in mice harboring a microbiota, neutralizing IL-17A dampened inflammation and restored lung function. CONCLUSIONS Collectively, our data indicate that host-microbial cross-talk promotes inflammation and could underlie the chronicity of inflammatory lung diseases.