Complement disorders and hereditary angioedema

The complement system testing in clinical laboratory

With the advancement in research in the field of the complement system, a more comprehensive understanding developed about the complement system's role in the life process of an organism. It is a system of innate immune surveillance. This system plays a pivotal role in host defense against pathogens, inflammation, B and T cell homeostasis. Complement system analysis has a significant advantage in the assessment of the immune system status, diagnosis and prognosis of diseases, and medication guidelines. Currently, complement system testing is neither yet widely used across all clinical laboratoriesnor are the testing protocols yet systematic. Based on the current research, it is suggested that the analysis of complement activator-activated complement activity and total complement activity would be comprehensively assessed to evaluate the complement system's immunological function, and combine of the detection of its components to establish a systematic protocol for the complement system testing in the clinical laboratory. This article reviews the complement system's physiological role, disease relevance and the current testing status in clinical laboratories. Further more, some suggestions have also been provided for the preparation of complement standards i.e., the standardized preparation process for complement standards seems to be a feasible option given the easy inactivation of complement.

The relevance of complement in pemphigoid diseases: A critical appraisal

Pemphigoid diseases are autoimmune chronic inflammatory skin diseases, which are characterized by blistering of the skin and/or mucous membranes, and circulating and tissue-bound autoantibodies. The well-established pathomechanisms comprise autoantibodies targeting various structural proteins located at the dermal-epidermal junction, leading to complement factor binding and activation. Several effector cells are thus attracted and activated, which in turn inflict characteristic tissue damage and subepidermal blistering. Moreover, the detection of linear complement deposits in the skin is a diagnostic hallmark of all pemphigoid diseases. However, recent studies showed that blistering might also occur independently of complement. This review reassesses the importance of complement in pemphigoid diseases based on current research by contrasting and contextualizing data from in vitro, murine and human studies.

First Analysis of SERPING1 Gene in Patients with Hereditary Angioedema in Colombia Reveals Two Genotypic Variants in a Highly Symptomatic Individual

Hereditary angioedema (HAE) is a heterogeneous genetic disease caused by a deficit in C1 inhibitor (C1-INH) and clinically characterized by sudden events of edema, swelling, and pruritus. Here, we describe the first SERPING1 genotyping in 22 subjects from 4 non-related families, all from southern Colombia. The previously reported heterozygous gene mutations, c.1081C>T (p.Gln361*), c.1396C>G (p.Arg466Gly), c.1029+84G>A, or c.106_107del (p.Ser36Phefs*21), were found in 12 patients. Of note, a single patient clinically characterized as severe HAE type 2 expressed mutations in exon 8 and intron 6, whereas all the others have type 1 HAE and expressed one pathogenic variant. One of the subjects, a 5-year-old girl was discovered to have a pathogenic variant, and she is still asymptomatic. This is the first report focused on HAE genetic analysis in a Colombian population.

Practice parameter for the diagnosis and management of primary immunodeficiency

The American Academy of Allergy, Asthma & Immunology (AAAAI) and the American College of Allergy, Asthma & Immunology (ACAAI) have jointly accepted responsibility for establishing the "Practice parameter for the diagnosis and management of primary immunodeficiency." This is a complete and comprehensive document at the current time. The medical environment is a changing environment, and not all recommendations will be appropriate for all patients. Because this document incorporated the efforts of many participants, no single individual, including those who served on the Joint Task Force, is authorized to provide an official AAAAI or ACAAI interpretation of these practice parameters. Any request for information about or an interpretation of these practice parameters by the AAAAI or ACAAI should be directed to the Executive Offices of the AAAAI, the ACAAI, and the Joint Council of Allergy, Asthma & Immunology. These parameters are not designed for use by pharmaceutical companies in drug promotion.

Complement system in dermatological diseases - fire under the skin

The complement system plays a key role in several dermatological diseases. Overactivation, deficiency, or abnormality of the control proteins are often related to a skin disease. Autoimmune mechanisms with autoantibodies and a cytotoxic effect of the complement membrane attack complex on epidermal or vascular cells can cause direct tissue damage and inflammation, e.g., in systemic lupus erythematosus (SLE), phospholipid antibody syndrome, and bullous skin diseases like pemphigoid. By evading complement attack, some microbes like Borrelia spirochetes and staphylococci can persist in the skin and cause prolonged symptoms. In this review, we present the most important skin diseases connected to abnormalities in the function of the complement system. Drugs having an effect on the complement system are also briefly described. On one hand, drugs with free hydroxyl on amino groups (e.g., hydralazine, procainamide) could interact with C4A, C4B, or C3 and cause an SLE-like disease. On the other hand, progress in studies on complement has led to novel anti-complement drugs (recombinant C1-inhibitor and anti-C5 antibody, eculizumab) that could alleviate symptoms in diseases associated with excessive complement activation. The main theme of the manuscript is to show how relevant the complement system is as an immune effector system in contributing to tissue injury and inflammation in a broad range of skin disorders.

Complement deficiencies in systemic lupus erythematosus

The complement system is a major, multifunctional part of innate immunity and serves as a bridge between the innate and adaptive immune systems. It consists of more than 30 distinct proteins that interact with one another in a specific sequence. There are three pathways of complement activation: the classical, the lectin, and the alternative pathways. The three pathways are initiated by distinct mechanisms, but they all generate the same core set of effector molecules. Inherited complete deficiencies in complement components are generally very rare and predispose to infections and autoimmune disease. One of the better described associations is between deficiencies in early classical pathway components and the development of systemic lupus erythematosus. The goal of this review will be to discuss the associations between and the causal mechanisms of complement deficiencies and systemic lupus erythematosus.

Postangioedema attack skin blisters: an unusual presentation of hereditary angioedema

Hereditary angioedema (HAE) is an autosomal dominant disorder characterised by attacks of self-limited swelling affecting extremities, face and intra-abdominal organs, most often caused by mutations in the C1-inhibitor gene with secondary Bradykinin-mediated increased vascular permeability. We describe a 36-year-old man with a history of HAE who presented with painful interdigital bullae secondary to an acute oedema exacerbation. Biopsy and cultures of the lesions were negative and they resolved spontaneously. It is important to highlight and recognise the development of oedema blisters after resolution of a flare of HAE (only 1 previous case report), and hence avoid unnecessary dermatological diagnostic workup and treatment.

Modulators of complement activation: a patent review (2008 - 2013)

INTRODUCTION

The architecture of the complement system has evolved during the last 600 - 700 million years to become an amazingly efficient and highly versatile alerting and cell killing device. Under physiological conditions, this system acts as a well-regulated cascade, protecting the organism against pathogens and participating during the initial defensive steps of humoral and cellular response. The unregulated activation of this system may cause or even aggravate diseases; therefore, its modulation is currently considered of high importance.

AREAS COVERED

This review is a critical examination on patent literature published between 2008 and 2013. An insight is provided about the discovery and development of novel therapeutic agents. These include macromolecules, polysaccharides and proteins, specific antibodies, and hybrid or chimeric products. Peptides and low molecular weight organic compounds (natural products, their derivatives and fully synthetic molecules) are covered as well.

EXPERT OPINION

The search of specific inhibitors of the complement cascade has become one of the Holy Grails of Medicinal Chemistry for the last 30 - 40 years, with very few cases of success. Some highly specific macromolecules are currently available as modulators of the complement. However, there is still a marked need to find new, more specific, efficient and convenient alternatives, especially suited for chronic administration, including novel inexpensive small molecule inhibitors. Analogously, despite the initial success with specific monoclonal antibodies, a vast territory is awaiting to be explored and conquered, regarding the regulation of complement activation by antibody-mediated blockage of specific polypeptides or receptor sites.

Membrane attack by complement: the assembly and biology of terminal complement complexes

Complement system activation plays an important role in both innate and acquired immunity. Activation of the complement and the subsequent formation of C5b-9 channels (the membrane attack complex) on the cell membranes lead to cell death. However, when the number of channels assembled on the surface of nucleated cells is limited, sublytic C5b-9 can induce cell cycle progression by activating signal transduction pathways and transcription factors and inhibiting apoptosis. This induction by C5b-9 is dependent upon the activation of the phosphatidylinositol 3-kinase/Akt/FOXO1 and ERK1 pathways in a Gi protein-dependent manner. C5b-9 induces sequential activation of CDK4 and CDK2, enabling the G1/S-phase transition and cellular proliferation. In addition, it induces RGC-32, a novel gene that plays a role in cell cycle activation by interacting with Akt and the cyclin B1-CDC2 complex. C5b-9 also inhibits apoptosis by inducing the phosphorylation of Bad and blocking the activation of FLIP, caspase-8, and Bid cleavage. Thus, sublytic C5b-9 plays an important role in cell activation, proliferation, and differentiation, thereby contributing to the maintenance of cell and tissue homeostasis.

Potentiation of C1-esterase inhibitor by heparin and interactions with C1s protease as assessed by surface plasmon resonance

BACKGROUND

Human C1-esterase inhibitor (C1-INH) is a multifunctional plasma protein with a wide range of inhibitory and non-inhibitory properties, mainly recognized as a key down-regulator of the complement and contact cascades. The potentiation of C1-INH by heparin and other glycosaminoglycans (GAGs) regulates a broad spectrum of C1-INH activities in vivo both in normal and disease states. SCOPE OF RESEARCH: We have studied the potentiation of human C1-INH by heparin using Surface Plasmon Resonance (SPR), circular dichroism (CD) and a functional assay. To advance a SPR for multiple-unit interaction studies of C1-INH we have developed a novel (consecutive double capture) approach exploring different immobilization and layout.

MAJOR CONCLUSIONS

Our SPR experiments conducted in three different design versions showed marked acceleration in C1-INH interactions with complement protease C1s as a result of potentiation of C1-INH by heparin (from 5- to 11-fold increase of the association rate). Far-UV CD studies suggested that heparin binding did not alter C1-INH secondary structure. Functional assay using chromogenic substrate confirmed that heparin does not affect the amidolytic activity of C1s, but does accelerate its consumption due to C1-INH potentiation.

GENERAL SIGNIFICANCE

This is the first report that directly demonstrates a significant acceleration of the C1-INH interactions with C1s due to heparin by using a consecutive double capture SPR approach. The results of this study may be useful for further C-INH therapeutic development, ultimately for the enhancement of current C1-INH replacement therapies.

A single nucleotide deletion at the C1 inhibitor gene as the cause of hereditary angioedema: insights from a Brazilian family

BACKGROUND

Hereditary angioedema is an autosomal dominant disease characterized by episodes of subcutaneous and submucosal edema. It is caused by deficiency of the C1 inhibitor protein, leading to elevated levels of bradykinin. More than 200 mutations in C1 inhibitor gene have been reported. The aim of this study was to analyze clinical features of a large family with an index case of hereditary angioedema and to determine the disease-causing mutation in this family.

METHODS

Family pedigree was constructed with 275 individuals distributed in five generations. One hundred and sixty-five subjects were interviewed and investigated for mutation at the C1 inhibitor gene. Subjects reporting a history of recurrent episodes of angioedema and/or abdominal pain attacks underwent evaluation for hereditary angioedema.

RESULTS

We have identified a novel mutation at the C1 inhibitor gene, c.351delC, which is a single-nucleotide deletion of a cytosine on exon 3, resulting in frameshift with premature stop codon. Sequencing analysis of the hypothetical truncated C1 inhibitor protein allowed us to conclude that, if transcription occurs, this protein has no biological activity. Twenty-eight members of the family fulfilled diagnostic criteria for hereditary angioedema and all of them presented the c.351delC mutation. Variation in clinical presentation and severity of disease was observed among these patients. One hundred and thirty-seven subjects without hereditary angioedema did not have the c.351delC mutation.

CONCLUSION

The present study provides definitive evidence to link a novel genetic mutation to the development of hereditary angioedema in patients from a Brazilian family.

Disease-causing mutations in genes of the complement system

Recent studies have revealed profound developmental consequences of mutations in genes encoding proteins of the lectin pathway of complement activation, a central component of the innate immune system. Apart from impairment of immunity against microorganisms, it is known that hereditary deficiencies of this system predispose one to autoimmune conditions. Polymorphisms in complement genes are linked to, for example, atypical hemolytic uremia and age-dependent macular degeneration. The complement system comprises three convergent pathways of activation: the classical, the alternative, and the lectin pathway. The recently discovered lectin pathway is less studied, but polymorphisms in the plasma pattern-recognition molecule mannan-binding lectin (MBL) are known to impact its level, and polymorphisms in the MBL-associated serine protease-2 (MASP-2) result in defects of complement activation. Recent studies have described roles outside complement and immunity of another MBL-associated serine protease, MASP-3, in the etiology of 3MC syndrome, an autosomal-recessive disorder involving a spectrum of developmental features, including characteristic facial dysmorphism. Syndrome-causing mutations were identified in MASP1, encoding MASP-3 and two additional proteins, MASP-1 and MAp44. Furthermore, an association was discovered between 3MC syndrome and mutations in COLEC11, encoding CL-K1, another molecule of the lectin pathway. The findings were confirmed in zebrafish, indicating that MASP-3 and CL-K1 underlie an evolutionarily conserved pathway of embryonic development. Along with the discovery of a role of C1q in pruning synapses in mice, these recent advances point toward a broader role of complement in development. Here, we compare the functional immunologic consequences of "conventional" complement deficiencies with these newly described developmental roles.

Innate immunity

Recent years have witnessed an explosion of interest in the innate immune system. Questions about how the innate immune system senses infection and empowers a protective immune response are being answered at the molecular level. These basic science discoveries are being translated into a more complete understanding of the central role innate immunity plays in the pathogenesis of many human infectious and inflammatory diseases. It is particularly exciting that we are already seeing a return on these scientific investments with the emergence of novel therapies to harness the power of the innate immune system. In this review we explore the defining characteristics of the innate immune system, and through more detailed examples, we highlight recent breakthroughs that have advanced our understanding of the role of innate immunity in human health and disease.