The immunoglobulin, IgG Fc receptor and complement triangle in autoimmune diseases

Analysis of heavy and light chain sequences of conventional camelid antibodies from Camelus dromedarius and Camelus bactrianus species

Camel antibodies have been widely investigated, but work has focused upon the unique heavy chain antibodies found across camelid species. These are homodimers, devoid of light chains and the first constant heavy chain domain. Camelid species also display conventional hetero-tetrameric antibodies with identical pairs of heavy and light chains; in Camelus dromedarius these constitute 25% of circulating antibodies. Few investigations have been made on this subset of antibodies and complete conventional camel IgG sequences have not been reported. Here we study the sequence diversity of functional variable and constant regions observed in 57 conventional heavy, 18 kappa and 35 lambda light chains of C. dromedarius and Camelus bactrianus. We detail sequences of the full kappa and lambda light chain, variable and CH1 region for IgG1a and IgG1b and the CH2 and CH3 region for IgG1a. The majority (60%) of IgG1 variable region sequences aligned with the human IgHV3 family (clan III) and had leader sequences beginning with MELG whereas the remaining sequences aligned with the IgHV4 (clan II) and had leader sequences beginning with MRLL. Distinct differences in CDR length were observed between the two; where CDR1 was typically 5 and 7 residues and CDR2 at 17 and 16 residues, respectively. CDR3 length of IgHV4 (range 11 to 20) was closer to that typical of VHH antibodies than that of IgHV3 (range 3 to 18 residues). Designed oligonucleotide primers have enabled identification of paired heavy and light chains of conventional camel antibodies from individual B cell clones.

Recombinant IgG2a Fc (M045) multimers effectively suppress experimental autoimmune myasthenia gravis

Myasthenia gravis (MG) is an autoimmune disorder caused by target-specific pathogenic antibodies directed toward postsynaptic neuromuscular junction (NMJ) proteins, most commonly the skeletal muscle nicotinic acetylcholine receptor (AChR). In MG, high-affinity anti-AChR Abs binding to the NMJ lead to loss of functional AChRs, culminating in neuromuscular transmission failure and myasthenic symptoms. Intravenous immune globulin (IVIg) has broad therapeutic application in the treatment of a range of autoimmune diseases, including MG, although its mechanism of action is not clear. Recently, the anti-inflammatory and anti-autoimmune activities of IVIg have been attributed to the IgG Fc domains. Soluble immune aggregates bearing intact Fc fragments have been shown to be effective treatment for a number of autoimmune disorders in mice, and fully recombinant multimeric Fc molecules have been shown to be effective in treating collagen-induced arthritis, murine immune thrombocytopenic purpura, and experimental inflammatory neuritis. In this study, a murine model of MG (EAMG) was used to study the effectiveness of this novel recombinant polyvalent IgG2a Fc (M045) in treating established myasthenia, with a direct comparison to treatment with IVIg. M045 treatment had profound effects on the clinical course of EAMG, accompanied by down-modulation of pathogenic antibody responses. These effects were associated with reduced B cell activation and T cell proliferative responses to AChR, an expansion in the population of FoxP3(+) regulatory T cells, and enhanced production of suppressive cytokines, such as IL-10. Treatment was at least as effective as IVIg in suppressing EAMG, even at doses 25-30 fold lower. Multimeric Fc molecules offer the advantages of being recombinant, homogenous, available in unlimited quantity, free of risk from infection and effective at significantly reduced protein loads, and may represent a viable therapeutic alternative to polyclonal IVIg.

Measurement and prevalence of circulating ADAMTS13-specific immune complexes in autoimmune thrombotic thrombocytopenic purpura

BACKGROUND

The formation of ADAMTS13-specific circulating immune complexes (CICs) may be a pathophysiologic mechanism in autoimmune thrombotic thrombocytopenic purpura (TTP), but has not been systematically investigated.

OBJECTIVES

(a) To develop an assay for ADAMTS13-specific CICs; (b) to evaluate their prevalence in autoimmune TTP; and (c) to assess their association with ADAMTS13-related measurements and clinical features in autoimmune TTP patients.

PATIENTS/METHODS

We developed and validated an ELISA method for ADAMTS13-specific CICs. ADAMTS13-specific CICs were searched for in 55 patients with autoimmune TTP from the Milan TTP Registry (URL:http://www.ttpdatabase.org/) and 28 controls. The associations between ADAMTS13-specific CIC levels and ADAMTS13 activity, antigen, anti-ADAMTS13 IgGs and acute TTP clinical features were assessed by multivariate linear regression.

RESULTS

Intra- and inter-assay coefficients of variation of the new test were 5.3 and 9.6%. In 36 patients with severe ADAMTS13 deficiency and anti-ADAMTS13 autoantibodies, the prevalence of ADAMTS13-specific CICs was 47% (n = 17; 95% confidence interval [CI], 32-63%). ADAMTS13-specific CICs were detected also in seven of 19 (37%; 95% CI, 19-59%) patients with reduced ADAMTS13 activity, but apparently negative anti-ADAMTS13 autoantibodies. ADAMTS13-specific CICs were not associated with ADAMTS13 activity, antigen or anti-ADAMTS13 IgGs. In patients with acute TTP, increasing levels of ADAMTS13-specific CICs were associated with a higher number of plasma-exchange procedures required to attain remission (per 0.1 increase in normalized OD values, beta, 2.9; 95% CI, -0.7 to 6.5).

CONCLUSIONS

Approximately one to two-thirds of patients with autoimmune TTP display ADAMTS13-specific CICs. A thorough investigation of the prognostic relevance of ADAMTS13-specific CIC levels in autoimmune TTP is warranted.

The multifaceted functions of neutrophils

Neutrophils and neutrophil-like cells are the major pathogen-fighting immune cells in organisms ranging from slime molds to mammals. Central to their function is their ability to be recruited to sites of infection, to recognize and phagocytose microbes, and then to kill pathogens through a combination of cytotoxic mechanisms. These include the production of reactive oxygen species, the release of antimicrobial peptides, and the recently discovered expulsion of their nuclear contents to form neutrophil extracellular traps. Here we discuss these primordial neutrophil functions, which also play key roles in tissue injury, by providing details of neutrophil cytotoxic functions and congenital disorders of neutrophils. In addition, we present more recent evidence that interactions between neutrophils and adaptive immune cells establish a feed-forward mechanism that amplifies pathologic inflammation. These newly appreciated contributions of neutrophils are described in the setting of several inflammatory and autoimmune diseases.

Michael F, Stupak J, Lewis LA, Ram S, Rice PA. Immunization against a saccharide epitope accelerates clearance of experimental gonococcal infection

The emergence of ceftriaxone-resistant strains of Neisseria gonorrhoeae may herald an era of untreatable gonorrhea. Vaccines against this infection are urgently needed. The 2C7 epitope is a conserved oligosaccharide (OS) structure, a part of lipooligosaccharide (LOS) on N gonorrhoeae. The epitope is expressed by 94% of gonococci that reside in the human genital tract (in vivo) and by 95% of first passaged isolates. Absence of the 2C7 epitope shortens the time of gonococcal carriage in a mouse model of genital infection. To circumvent the limitations of saccharide immunogens in producing long lived immune responses, previously we developed a peptide mimic (called PEP1) as an immunologic surrogate of the 2C7-OS epitope and reconfigured it into a multi-antigenic peptide, (MAP1). To test vaccine efficacy of MAP1, female BALB/c mice were passively immunized with a complement-dependent bactericidal monoclonal antibody specific for the 2C7 epitope or were actively immunized with MAP1. Mice immunized with MAP1 developed a TH1-biased anti-LOS IgG antibody response that was also bactericidal. Length of carriage was shortened in immune mice; clearance occurred in 4 days in mice passively administered 2C7 antibody vs. 6 days in mice administered control IgG3λ mAb in one experiment (p = 0.03) and 6 vs. 9 days in a replicate experiment (p = 0.008). Mice vaccinated with MAP1 cleared infection in 5 days vs. 9 days in mice immunized with control peptide (p = 0.0001 and p = 0.0002, respectively in two replicate experiments). Bacterial burden was lower over the course of infection in passively immunized vs. control mice in both experiments (p = 0.008 and p = 0.0005); burdens were also lower in MAP1 immunized mice vs. controls (p<0.0001) and were inversely related to vaccine antibodies induced in the vagina (p = 0.043). The OS epitope defined by mAb 2C7 may represent an effective vaccine target against gonorrhea, which is rapidly becoming incurable with currently available antibiotics.

Dominant suppression of inflammation by glycan-hydrolyzed IgG

A unique anti-inflammatory property of IgG, independent of antigen specificity, is described. IgG with modification of the heavy-chain glycan on asparagine 297 by the streptococcal enzyme endo-β-N-acetylglucosaminidase (EndoS) induced a dominant suppression of immune complex (IC)-mediated inflammation, such as arthritis, through destabilization of local ICs by fragment crystallizable-fragment crystallizable (Fc-Fc) interactions. Small amounts (250 µg) of EndoS-hydrolyzed IgG were sufficient to inhibit arthritis in mice and most effective during the formation of ICs in the target tissue. The presence of EndoS-hydrolyzed IgG disrupted larger IC lattice formation both in vitro and in vivo, as visualized with anti-C3b staining. Neither complement binding in vitro nor antigen-antibody binding per se was affected.

Complement in immune and inflammatory disorders: pathophysiological mechanisms

Although acute or chronic inflammation is a common component of many clinical disorders, the underlying processes can be highly distinct. In recent years, the complement system has been associated with a growing number of immunological and inflammatory conditions that include degenerative diseases, cancer, and transplant rejection. It becomes evident that excessive activation or insufficient control of complement activation on host cells can cause an immune imbalance that may fuel a vicious cycle between complement, inflammatory cells, and tissue damage that exacerbates clinical complications. Although the exact involvement of complement needs to be carefully investigated for each disease, therapeutic modulation of complement activity emerges as an attractive target for upstream inhibition of inflammatory processes. This review provides an update about the functional and collaborative capabilities of complement, highlights major disease areas with known complement contribution, and indicates the potential for complement as a focal point in immunomodulatory strategies for treating inflammatory diseases.

Epidermolysis bullosa acquisita

Epidermolysis bullosa acquisita (EBA) is a chronic autoimmune subepidermal bullous disease with clinical features similar to the genetic form of dystrophic epidermolysis bullosa. EBA is characterized by the presence of autoantibodies against type VII collagen which is a major component of the anchoring fibrils at the dermal-epidermal junction. EBA can be divided into two main clinical types; mechanobullous and inflammatory EBA. Mechanobullous EBA, referred to as classic EBA, presents with skin fragility, blisters and dystrophic changes on trauma-prone areas. Inflammatory EBA resembles other autoimmune subepidermal bullous diseases. Compelling evidence from mouse models supports a pathogenic role of autoantibodies against type VII collagen in EBA. Treatment of EBA is often unsatisfactory. The most widely used systemic treatment is corticosteroids. Colchicine and dapsone have been reported to be good treatment modalities when combined with corticosteroids. Some intractable cases of EBA have successfully been treated with intravenous immunoglobulin or rituximab.