Complement deficiency

Systemic Lupus Erythematosus and Deficiencies of Early Components of the Complement Classical Pathway

The complement system plays an important role in the innate and acquired immune response against pathogens. It consists of more than 30 proteins found in soluble form or attached to cell membranes. Most complement proteins circulate in inactive forms and can be sequentially activated by the classical, alternative, or lectin pathways. Biological functions, such as opsonization, removal of apoptotic cells, adjuvant function, activation of B lymphocytes, degranulation of mast cells and basophils, and solubilization and clearance of immune complex and cell lysis, are dependent on complement activation. Although the activation of the complement system is important to avoid infections, it also can contribute to the inflammatory response triggered by immune complex deposition in tissues in autoimmune diseases. Paradoxically, the deficiency of early complement proteins from the classical pathway (CP) is strongly associated with development of systemic lupus erythematous (SLE) - mainly C1q deficiency (93%) and C4 deficiency (75%). The aim of this review is to focus on the deficiencies of early components of the CP (C1q, C1r, C1s, C4, and C2) proteins in SLE patients.

Hereditary angioedema and lupus: A French retrospective study and literature review

Hereditary angioedema (HAE) is a rare genetic disorder that is primarily caused by a defect in the C1 inhibitor (C1-INH). The recurrent symptoms are subcutaneous edema and abdominal pain. Laryngeal edema, which can also occur, is life threatening if it goes untreated. HAE can be associated with some inflammatory and autoimmune disorders, particularly lupus. The aim of this study was to describe cases of lupus among HAE patients in France and to perform a literature review of lupus and HAE studies. Case detection and data collection (a standardized form) were performed, thanks to the French Reference Center for Kinin-related angioedema. Data were collected from 6 patients with type 1 HAE and lupus in France; no cases of systemic lupus erythematosus were reported. In the literature review, 32 cases of lupus combined with HAE were identified, including 26 female patients. The median patient age at the time of first reported HAE symptoms and at diagnosis were 17.5 years (range, 9-41 years) and 19 years (range, 9-64 years), respectively for our 6 patients and 14 years (range, 3-30 years) and 17 years (range, 7-48 years), respectively, for the literature review. The clinical manifestations of HAE were mainly abdominal pain (83% in our patients vs 47% in the literature) and edema of the limbs (83% vs 38%). The C4 levels were low (for 100% of our cases vs 93% in the literature). Eighteen patients in the literature demonstrated HAE symptoms prior to the lupus onset vs 5 for our patients. The mean patient age at lupus onset was 20 years (range, 13-76 years) for our patients and 19.5 years (range, 1-78 years) in the literature, respectively. In the literature, 81% of the patients had skin manifestations, 25% had renal involvement and 28% received systemic steroids to treat lupus. Treatment with danazol did not modify the clinical expression of lupus. The association between lupus and HAE is a rare but not unanticipated event. Patients are often symptomatic for HAE before developing lupus. Lupus cases associated with HAE share some characteristics of lupus cases related to other complement deficiencies, such as the absence of severity and the predominance of cutaneous symptoms.

The complement system in pediatric systemic lupus erythematosus, atypical hemolytic uremic syndrome, and complocentric membranoglomerulopathies

PURPOSE OF REVIEW

This review summarizes the recent advances in complement biology and the evolving understanding of these contributions to the pathophysiology and treatment of predominantly pediatric disease syndromes.

RECENT FINDINGS

Identification of lupus patients with complete deficiencies of one of the plasma complement proteins enabled the field to move beyond the notion of complement as a laboratory curiosity. Clinical investigation of the manifestations observed in deficient patients has further defined the biology of the system in normal individuals. Definition of the assembly of the C3 convertases, particularly that of the alternative pathway and its regulation, has led to the appreciation that the complement system includes membrane inhibitors that are every bit as important as those in plasma. The exploration of disease states in which significant complement deposition occurs has moved the field away from consideration of this finding as a bystander effect. Dissection of these syndromes has led to the unanticipated finding of a central role for function-altering mutations in the complement proteins that form or regulate the alternative pathway C3 convertase and has opened the door to new therapeutic approaches. The disease states discussed in the review - pediatric systemic lupus erythematosus, atypical hemolytic uremic syndrome, and the complocentric membranoglomerulopathies - illustrate this evolutionary history of complement biology.

SUMMARY

This review emphasizes that both the lack of classical pathway complement activation and excessive activation of the alternative pathway contribute to distinct disease pathogenesis, and emphasizes the critical importance of homeostatic regulation, in both plasma and in tissues, of the system as a whole.

Disseminated intravascular coagulation, meningococcal infection, and ischemic changes affecting the lower extremities: a case study

A middle-aged woman presented from an outside hospital with a diagnosis of Neisseria meningitidis and meningococcemia. A nonpalpable purpuric skin rash evolved into multiple wounds, with gradual necrosis of bilateral lower and upper extremities. Throughout the course of hospitalization, the patient developed ventricular tachycardia, normocytic anemia, thrombocytosis, Clostridium difficile infection, depression, and transient right eye blindness. The finding of decreased CH50 in the complement cascade was considered as the potential cause of the meningococcemia. The subsequent ischemia and necrosis of extremities were attributed to the systemic effect and trauma ensuing from N. meningitidis.

Clinical significance of complement deficiencies

The complement system is composed of more than 30 serum and membrane-bound proteins, all of which are needed for normal function of complement in innate and adaptive immunity. Historically, deficiencies within the complement system have been suspected when young children have had recurrent and difficult-to-control infections. As our understanding of the complement system has increased, many other diseases have been attributed to deficiencies within the complement system. Generally, complement deficiencies within the classical pathway lead to increased susceptibility to encapsulated bacterial infections as well as a syndrome resembling systemic lupus erythematosus. Complement deficiencies within the mannose-binding lectin pathway generally lead to increased bacterial infections, and deficiencies within the alternative pathway usually lead to an increased frequency of Neisseria infections. However, factor H deficiency can lead to membranoproliferative glomerulonephritis and hemolytic uremic syndrome. Finally, deficiencies within the terminal complement pathway lead to an increased incidence of Neisseria infections. Two other notable complement-associated deficiencies are complement receptor 3 and 4 deficiency, which result from a deficiency of CD18, a disease known as leukocyte adhesion deficiency type 1, and CD59 deficiency, which causes paroxysmal nocturnal hemoglobinuria. Most inherited deficiencies of the complement system are autosomal recessive, but properidin deficiency is X-linked recessive, deficiency of C1 inhibitor is autosomal dominant, and mannose-binding lectin and factor I deficiencies are autosomal co-dominant. The diversity of clinical manifestations of complement deficiencies reflects the complexity of the complement system.

Risk of non-Hodgkin lymphoma in association with germline variation in complement genes

Germline mutations in complement genes have been associated with susceptibility to infections and autoimmune diseases, conditions that are associated with non-Hodgkin lymphoma (NHL) risk. To test the hypothesis that common genetic variation in complement genes affect risk of NHL, we genotyped 167 single nucleotide polymorphisms (SNPs) from 31 genes in 441 NHL cases and 475 controls. Principal components (PC) and haplotype analyses were used for gene-level tests of NHL risk, while individual SNPs were modelled as having a log-additive effect. In gene level PC analyses, C2 (P = 0.023), C5 (P = 0.0032) and C9 (P = 0.020) were associated with NHL risk; haplotype analyses showed similar results, as well as a haplotype association for C7 (P = 0.046). When all four genes were considered simultaneously, only C5 and C9 remained significant (P < 0.05). In SNP level results from these genes, 10 SNPs had a P < 0.05. However, after correcting for multiple testing, only the C5 SNPs rs7026551 (q = 0.015; OR = 1.54, 95% CI 1.21-1.95) and rs2416810 (q = 0.015; OR = 1.57; 95% CI 1.22-2.01), and the C9 SNP rs187875 (q = 0.015; OR = 0.68; 95% 0.56-0.84) remained noteworthy. Associations were similar for the common NHL subtypes. In summary, we provide evidence for a role of genetic variation in complement genes, particularly C5 and C9, and NHL risk.

12. Primary immunodeficiency diseases

Although primary immunodeficiency disorders are relatively rare, intensive investigation of these disorders has yielded a great wealth of understanding of basic immunologic mechanisms in host defense, inflammation, and autoimmunity. These advances have led to important developments for the treatment not only of the primary immunodeficiencies but also for patients with secondary immunocompromised states, autoimmune disorders, hypersensitivity, graft rejection, and graft versus host disease. Correction of a form of severe combined immunodeficiency represents the first true success of human gene therapy. This review introduces the major clinical manifestations of primary immunodeficiency disorders, along with descriptions of essential elements of the pathophysiology of those disorders that have been defined at the molecular level. Key concepts in treatment are also presented. It is critical for the practicing primary care provider and allergist to maintain an index of suspicion for immunodeficiency. Early diagnosis offers the best opportunity for reduced morbidity and survival and is critical for accurate genetic counseling.

Rheumatic syndromes associated with complement deficiency

Deficiency of an early component of the classical complement pathway, C1q, C1r/C1s, C4, or C2, regularly produces autoimmunity in man, especially systemic lupus erythematosus. It has long been suggested that disruption of this pathway would lead to the inappropriate handling of immune complexes. An intriguing hypothesis that builds on this idea relates to a defect in clearance of one's own cellular debris, namely apoptotic cells. An attractive feature of this emerging concept is that blebs on apoptotic cells are decorated with antigens to which much of the autoantibody specificity is directed in systemic lupus erythematosus. A second hypothesis, generated primarily from complement deficiencies, relates to an impairment in the humoral immune response or in the regulation of autoreactive B cells. This review begins by summarizing the recognized autoimmune manifestations of complement deficiency and then describes new data derived from targeted gene deletions of complement proteins.