Epidemiology of hypocomplementaemic urticarial vasculitis (anti-C1q vasculitis).

Objectives: The aim was to describe the clinical characteristics and epidemiology of hypocomplementaemic urticarial vasculitis (HUV; anti-C1q vasculitis) in two geographically defined areas of Sweden. Methods: In the health-care districts surrounding Skåne University Hospital (mean population 950 560) and Linköping University Hospital (mean population 428 503), all incident cases of HUV residing within the study areas at the onset of disease were identified during the years 2000-15. The diagnosis of HUV was confirmed by review of medical records. Only patients meeting the proposed diagnostic HUV criteria and/or the 2012 Chapel Hill consensus definitions in combination with an ever-positive anti-C1q antibody test were included. Results: Sixteen patients (14 females) were identified during the study period. The median (interquartile range) age at diagnosis was 51 (40.7-56.7) years. Median (interquartile range) time of follow-up from diagnosis to 31 December 2015, or death, was 94 (46.5-136.2) months. The most frequent manifestations at diagnosis were urticaria (100%), arthritis (88%), followed by biopsy-proven glomerulonephritis (19%), episcleritis/scleritis (19%) and recurrent abdominal pain (13%). The annual incidence rate per million inhabitants was estimated as 0.7 (95% CI: 0.4, 1.1). Sixty-three per cent suffered from pulmonary disease at the last follow-up. Two patients died during the follow-up period. One patient underwent lung transplantation, and two patients proceeded to end-stage renal disease. The point prevalence on 31 December 2015 was 9.5/million (95% CI: 4.5, 14.5). Conclusion: Hypocomplementaemic urticarial vasculitis constitutes a rare, but not always benign condition. Renal and lung manifestations were severe in some cases, highlighting the need for careful screening and monitoring of this potentially serious condition.

Immunogenicity and safety of pneumococcal vaccination in patients with systemic sclerosis.

Objective: To study the impact of disease and treatment with DMARDs on antibody response elicited by either pneumococcal conjugate vaccine (PCV13) or pneumococcal polysaccharide vaccine (PPV23) in patients with SSc. Methods: Forty-four SSc patients and 49 controls received a dose of either PCV13 or PPV23. Twelve patients were treated with DMARDs. Antibody levels to pneumococcal polysaccharides 6B and 23 F were measured before and 4-6 weeks after vaccination using ELISA. Antibody functionality was studied using opsonophagocytic assay performed on serotype 23 F. Results: Number of patients, percentage female and mean age (years) at vaccination were: 32, 94%, 57.5 years in SSc without DMARDs; 12, 100%, 55.5 years in SSc on DMARDs and 49, 63% and 50.6 years in controls. Post-vaccination antibody levels for both serotypes increased significantly in SSc without DMARDs and controls (P < 0.001), but in SSc on DMARDs only for 6B (P = 0.041). Compared with the other groups, patients with SSc receiving DMARDs had lower post-vaccination antibody levels for both serotypes. Opsonophagocytic assay increased significantly in all three groups. No significant difference in immunogenicity between PCV13 and PPV23 was seen. Conclusion: Pneumococcal vaccination using either PCV13 or PPV23 yielded satisfactory antibody response in SSc patients without DMARD treatment, but a lower response in patients treated with synthetic DMARDs. Type of pneumococcal vaccine (conjugate or polysaccharide) did not significantly influence antibody response. Trial registration: ClinicalTrials.gov, http://clinicaltrials.gov, NCT02240888.

Primary immunodeficiency in infection-prone children in southern Sweden: occurrence, clinical characteristics and immunological findings.

BACKGROUND: Primary immunodeficiency diseases (PIDs) comprise a heterogeneous group of disorders mainly characterized by increased susceptibility to infections. The aims of this study were to estimate the occurrence rate of PID in the paediatric (age ≤ 18 years) population of southern Sweden (approx. 265,000 children) and to describe their demographic, clinical and immunological characteristics. During a period of 4 years, in four paediatric speciality clinics in Skåne County in southern Sweden, children being seen for infections and fulfilling specific criteria were evaluated according to a predefined examination schedule. The initial analysis consisted of complete blood counts with analysis of lymphocyte subpopulations (T, B, NK cells), measurement of immunoglobulins (IgG, IgA, IgM, IgE and IgG subclasses), and assessment of the complement system (classical, alternative and lectin pathways). In addition, results of these immunological analyses in other children from the same area and time period were evaluated. RESULTS: In total, 259 children (53.6% males) met the criteria and were included. The most common infection was recurrent otitis media. Immunological analyses results for about two thirds of the patients were outside age-related reference intervals. Further examination in this latter group identified 15 children with PID (9 males); 7 (2.7%) had genetically defined PID, representing 4 different diagnoses, and another 8 (3.1%) had a clinically defined PID - common variable immunodeficiency. No additional PID patient was identified from the evaluation of laboratory results in children not included in the study. The median age at diagnosis was 3.5 years (range 1-12 years). CONCLUSIONS: The occurrence rate of PID was about 4 new cases per year in this population. Several different PID diagnoses were found, and the application of specified criteria to identify PID patients was useful. In children who are prone to infection, the use of a predefined set of immunological laboratory analyses at their first examination was beneficial for early identification of patients with PID.

The response to vaccination against influenza A(H1N1) 2009, seasonal influenza and Streptococcus pneumoniae in adult outpatients with ongoing treatment for cancer with and without rituximab.

UNLABELLED: It is debated whether cancer patients treated with chemotherapy can mount an adequate response to vaccination. MATERIAL AND METHODS: Ninety-six adult outpatients with cancer, who were undergoing chemotherapy and/or monoclonal antibody, tyrosine kinase inhibitor, irradiation or corticosteroid treatments, were studied. Two doses of the pandemic influenza A(H1N1)/09 AS03-adjuvanted split virion vaccine, one dose of the seasonal influenza vaccine and one dose of the 23-valent pneumococcal polysaccharide vaccine were given. Serum haemagglutination inhibition (HI) assays were used to determine antibody titres against the influenza strains. For the pneumococcal vaccine 14 different serotype-specific anti-capsular antibodies were measured by bead assay xMAP(®). RESULTS: Patients treated with rituximab did not respond to vaccination. For patients without rituximab treatment 4% had putatively protective antibodies before vaccination (HI ≥ 40) to the pandemic-like strain A/California7/2009HINI. After the first and second dose of vaccine, seroprotection rates (SPR) were 62% and 87%, and seroconversion rates (SCR) 62% and 84%, respectively. Before seasonal flu vaccination SPR against influenza A/Brisbane/59/2007H1N1 and A/Uruguay/10/2007H3N2 were 19% and 17%, respectively. After vaccination, SPR were 70% and 59% and SCR 42% and 50%, respectively. For the pneumococcal vaccine protective antibodies were found to 40% of the 14 strains before and to 68% after vaccination. The mean response to pneumococcal vaccination was to 44% of the 14 serotypes. A response to at least 50% of the 14 serotypes was found in 49% of the patients. No serious adverse events were reported. CONCLUSION: A substantial number of adult cancer patients with ongoing chemotherapy treatment could mount an adequate serological response to influenza and pneumococcal vaccination without severe adverse events. Thus, vaccination should be recommended. Adjuvanted vaccines may improve the vaccine response among this patient group. Patients recently treated with rituximab do not respond to vaccination.

Complement Components in Peripheral Blood from Adult Patients with IDH Wild-Type Glioblastoma.

BACKGROUND: The complement system seems to influence cancer pathophysiology. The primary aim of this study was to explore complement components associated with the classical pathway (CP) of the complement system in peripheral blood from patients with IDH-wild-type (IDH-wt) glioblastoma. METHODS: Patients undergoing primary surgery due to glioblastoma in the years 2019-2021 were prospectively included in the present study. Blood samples were collected prior to surgery, and analyzed with regard to CP complement components, as well as standard coagulation tests. RESULTS: In total, 40 patients with IDH-wt glioblastomas were included. C1q was reduced in 44% of the cases compared to the reference interval. C1r was reduced in 61% of the analyzed samples. Both C1q and C1r are parts of the initial steps of the classical complement activation pathway, which, however, was not correspondingly altered. Activated pro-thromboplastin time (APTT) was shorter in 82% of the analyzed samples compared to the reference interval. APTT was shorter in those with reduced C1q and C1r levels. C1q is an important link between the innate and acquired immunity, and C1q and C1r also interact with the coagulation system. Patients who displayed reduced levels of both C1q and C1r preoperatively had a significantly shorter overall survival compared with the rest of the cohort. CONCLUSIONS: Our findings demonstrate that there are alterations in C1q and C1r concentrations in peripheral blood from patients with IDH1-wt glioblastoma compared with the normal population. Patients who displayed reduced C1q and C1r levels had a significantly shorter survival.

Complement C1s deficiency in a male Caucasian patient with systemic lupus erythematosus: a case report.

Deficiencies of the early complement components of the classical pathway (CP) are well-documented in association with systemic lupus erythematosus (SLE) or SLE-like syndromes and severe pyogenic infections. Among these, complete C1s deficiency has been reported in nine cases so far. Here, we describe a 34-year-old male patient who presented with severe, recurrent infections since childhood, including meningitides with pneumococci and meningococci, erysipelas, subcutaneous abscess, and recurrent infections of the upper airways. The patient also exhibited adult-onset SLE, meeting 7/11 of the ACR criteria and 34 of the 2019 EULAR/ACR classification criteria, along with class IV-G (A) proliferative lupus nephritis (LN). A screening of the complement cascade showed immeasurably low CH50, while the alternative pathway (AP) function was normal. Subsequent determination of complement components revealed undetectable C1s with low levels of C1r and C1q, normal C3, and slightly elevated C4 and C2 concentrations. The patient had no anti-C1q antibodies. Renal biopsy showed class IV-G (A) LN with complement C1q positivity along the glomerular basement membranes (GBMs) and weak deposition of IgG, IgM, and complement C3 and C4 in the mesangium and GBM. In an ELISA-based functional assay determining C4d deposition, the patient's absent complement activity was fully restored by adding C1s. The genome of the patient was analyzed by whole genome sequencing showing two truncating variants in the C1S gene. One mutation was located at nucleotide 514 in exon 5, caused by a nucleotide substitution from G to T, resulting in a nonsense mutation from Gly172 (p.Gly172*). The other mutation was located at nucleotide 750 in exon 7, where C was replaced by a G, resulting in a nonsense mutation from Tyr250 (p.Tyr250*). Both mutations create a premature stop codon and have not previously been reported in the literature. These genetic findings, combined with the absence of C1s in the circulation, strongly suggest a compound heterozygote C1s deficiency in our patient, without additional defect within the complement cascade. As in a previous C1s deficiency case, the patient responded well to rituximab. The present case highlights unanswered questions regarding the CP's role in SLE etiopathogenesis.

Sensitive and specific assays for C3 nephritic factors clarify mechanisms underlying complement dysregulation.

C3 nephritic factors are autoantibodies that prolong the half-life or prevent regulation of the alternative pathway C3 convertase, resulting in uncontrolled complement activation. They are strongly associated with renal disease but their role in pathogenesis remains controversial. Here we optimized and compared a panel of assays to identify and interrogate nephritic factor activities. Of 101 patients with histologic or clinically evident disease, 48 were positive in some or all assays. In the presence of properdin, binding of autoantibody was detected in 39 samples and convertase stabilization was detected in 36. Forty-two of 48 nephritic factors tested prevented convertase decay by factor H, and most of these by decay accelerating factor (28) and complement receptor 1 (34). Representative properdin-independent nephritic factors had no effect on C5 cleavage and terminal pathway activity, while properdin-dependent nephritic factors enhanced activity. Biacore analysis of four purified IgG samples confirmed resistance to decay and showed that properdin-independent nephritic factors increased convertase half-life over 50-fold, whereas properdin-dependent nephritic factors increased the half-life 10- to 20-fold and also increased activity of the C3 convertase up to 10-fold. Thus, our study provides a rational approach to detect and characterize nephritic factors in patients.

Comorbidities in hereditary angioedema-A population-based cohort study.

BACKGROUND: In hereditary angioedema (HAE), low levels (type 1) or defect in function (type 2) of the serine-protease inhibitor C1 Inhibitor protein results in activation of the classical pathway of the complement system as well as the contact system. Here, we investigated the risk of comorbidities in HAE. METHODS: Individuals with HAE (n = 239; identified through a physician made diagnosis) and a control cohort from the general population (n = 2383; matched for age, gender, and county of residence) were compared with the Swedish inpatient, cause of death, cancer, and prescription registers. Conditional logistic regression was used to analyze the data. RESULTS: Increased risk of cardiovascular disease (odds ratio [OR] 1.83; 95% confidence interval [CI] 1.32-2.54), including arterial (OR 6.74; 95% CI 1.89-24.06) and venous thromboembolic disease (OR 4.20; 95% CI 2.42-7.23) as well as hypertension (OR 1.64; 95% CI 1.12-2.39) was seen in HAE. There was also an increased number of individuals diagnosed with hyperlipidemia (OR 2.01; 95% CI 1.16-3.50) among HAE patients. Furthermore, the risk of autoimmune disease was increased (OR 1.65; 95% CI 1.15-2.35) being particularly pronounced for systemic lupus erythematosus (OR 71.87; 95% CI 8.80-586.7). The risk of having two or more autoimmune diseases was also higher among HAE patients (p = 0.017). In contrast, the risk of cancer was not increased. Data from the prescription register revealed higher prescription rates of drugs against hypertension, hypothyroidism, and hyperlipidemia among HAE patients. CONCLUSIONS: The results warrant for awareness and prevention of comorbid conditions, in particular, thromboembolic and autoimmune diseases in HAE. Future prophylactic interventions may modify these risks.

Methotrexate Treatment Suppresses Monocytes in Nonresponders to Pneumococcal Conjugate Vaccine in Rheumatoid Arthritis Patients.

Patients with rheumatoid arthritis (RA) have an increased risk of infections; therefore, immunization against vaccine-preventable diseases is important. Methotrexate (MTX) impairs the antibody response to pneumococcal conjugate vaccine (PCV) in patients with arthritis, and the underlying mechanism is largely unknown. Here, we investigate the potential role of the innate immune system in the faltering antibody response following PCV vaccination in RA patients treated with MTX. Phenotypes of circulating granulocytes and monocytes were analyzed in 11 RA patients treated with MTX, 13 RA patients without disease-modifying antirheumatic drug treatment (0DMARD), and 13 healthy controls (HC). Peripheral blood samples were collected before and 7 days after vaccination. In addition, the MTX group was sampled before initiating treatment. Frequencies of granulocyte and monocyte subsets were determined using flow cytometry. Serotype-specific IgG were quantified using a multiplex bead assay, pre- and 4-6 weeks after vaccination. At baseline, no differences in granulocyte and monocyte frequencies were observed between the groups. Within the MTX group, the frequency of basophils increased during treatment and was higher compared to the HC and 0DMARD groups at the prevaccination time point. MTX patients were categorized into responders and nonresponders according to the antibody response. Before initiation of MTX, there were no differences in granulocyte and monocyte frequencies between the two subgroups. However, following 6-12 weeks of MTX treatment, both the frequency and concentration of monocytes were lower in PCV nonresponders compared to responders, and the difference in monocyte frequency remained after vaccination. In conclusion, the suppressive effect of MTX on monocyte concentration and frequency could act as a biomarker to identify nonresponders to PCV vaccination.

Increased serum bactericidal activity of autologous serum in C2 deficiency after vaccination against Haemophilus influenzae type b, and further support for an MBL-dependent C2 bypass mechanism.

Deficiencies of C2 and other components of the classical pathway of complement are associated with increased risk of infections with encapsulated bacteria, such as Haemophilus (H.) influenzae. Defense against H. influenzae is dependent on specific antibodies and complement, which mediate serum bactericidal activity (SBA) and opsonization. Due to lack of normal classical and lectin complement pathway function in C2 deficiency (C2D), SBA would have to depend either on the alternative pathway or on C2 bypass mechanisms. Here we studied SBA against H. influenzae type b (Hib) before and after vaccination in a group of C2-deficient persons, as the bactericidal capacity of antibodies in autologous complement in relation to vaccination has not been investigated at group level in C2D. Sera from 22 persons with C2D and 26 healthy controls were available. Out of these, 18 persons with C2D and all controls had been vaccinated with Act-HIB®. SBA against Hib bacteria was analyzed with autologous serum as the only complement source. Antibodies to Hib capsular polysaccharide had been analyzed previously. Concentrations of mannose-binding lectin (MBL) and other complement components were measured in serum. SBA of both C2-deficient persons and controls was significantly more efficient after vaccination (p = 0.002 and p < 0.0001, respectively). After vaccination, all but two C2-deficient sera and one control serum showed sufficient SBA (<50% surviving bacteria). Before vaccination, SBA of C2-deficient sera was negatively correlated to serum concentrations of MBL (lower proportion of surviving bacteria with higher MBL concentration; r = -0.55, p = 0.008). After vaccination, SBA of C2-deficient sera was negatively correlated to serum concentrations of IgG Hib antibodies (r = -0.56, p = 0.01). In conclusion, SBA against Hib in autologous serum is increased after vaccination in persons with C2D. In unvaccinated C2-deficient persons SBA was correlated to MBL concentration, providing further support for an MBL-dependent C2 bypass mechanism operating in C2D.

Methotrexate reduces circulating Th17 cells and impairs plasmablast and memory B cell expansions following pneumococcal conjugate immunization in RA patients.

Methotrexate (MTX) impairs antibody response after pneumococcal vaccination. We aimed to investigate differences in phenotypes of circulating B and T cells after pneumococcal conjugate vaccine (PCV) in rheumatoid arthritis (RA) patients on MTX (MTX group), RA without disease-modifying drugs (0DMARD), and controls (HC). MTX group (n = 11), 0DMARD (n = 12) and HC (n = 13) were studied. Blood samples were collected: before MTX, ≥ 4 weeks on stable MTX dose (prevaccination), and 7 days postvaccination (MTX group), and pre- and 7 days postvaccination (0DMARD and HC). Phenotypes of B- and T cell subsets were determined using flow cytometry. Serotype-specific IgG were quantified using multiplex bead assay, pre- and 4-6 weeks postvaccination. Concentrations of plasmablasts and switched memory B cells increased after PCV in HC (both p = 0.03) and the 0DMARD group (p = 0.01 and p = 0.02), but not in the MTX group. Postimmunization plasmablasts were lower in MTX group, compared to the 0DMARD group and HC (p = 0.002 and p < 0.001). Th17 cells decreased after MTX start (p = 0.02), and increased in HC after immunization (p = 0.01). Postimmunization plasmablasts correlated with mean antibody response ratio in all RA patients (R = 0.57, p = 0.035). Methotrexate reduced Th17 cells and blocked activation of plasmablasts and switched memory B cells following polysaccharide-protein conjugate antigen challenge in RA.

Increased Frequencies of Switched Memory B Cells and Plasmablasts in Peripheral Blood from Patients with ANCA-Associated Vasculitis.

B cells are thought to play a central role in the pathogenesis of antineutrophil cytoplasmic antibody- (ANCA-) associated vasculitis (AAV). ANCAs have been proposed to cause vasculitis by activating primed neutrophils to damage small blood vessels. We studied a cohort of AAV patients of which a majority were in remission and diagnosed with granulomatosis with polyangiitis (GPA). Using flow cytometry, the frequencies of CD19+ B cells and subsets in peripheral blood from 106 patients with AAV and 134 healthy controls were assessed. B cells were divided into naive, preswitch memory, switched memory, and exhausted memory cells. Naive and switched memory cells were further subdivided into transitional cells and plasmablasts, respectively. In addition, serum concentrations of immunoglobulin A, G, and M were measured and clinical data were retrieved. AAV patients displayed, in relation to healthy controls, a decreased frequency of B cells of lymphocytes (5.1% vs. 8.3%) and total B cell number. For the subsets, a decrease in percentage of transitional B cells (0.7% vs. 4.4%) and expansions of switched memory B cells (22.3% vs. 16.5%) and plasmablasts (0.9% vs. 0.3%) were seen. A higher proportion of B cells was activated (CD95+) in patients (20.6% vs. 10.3%), and immunoglobulin levels were largely unaltered. No differences in B cell frequencies between patients in active disease and remission were observed. Patients in remission with a tendency to relapse had, compared to nonrelapsing patients, decreased frequencies of B cells (3.5% vs. 6.5%) and transitional B cells (0.1% vs. 1.1%) and an increased frequency of activated exhausted memory B cells (30.8% vs. 22.3%). AAV patients exhibit specific changes in frequencies of CD19+ B cells and their subsets in peripheral blood. These alterations could contribute to the autoantibody-driven inflammatory process in AAV.

Prime-boost vaccination strategy enhances immunogenicity compared to single pneumococcal conjugate vaccination in patients receiving conventional DMARDs, to some extent in abatacept but not in rituximab-treated patients.

OBJECTIVE: To explore whether a prime-boost vaccination strategy, i.e., a dose of pneumococcal conjugate vaccine (PCV) and a dose of 23-valent polysaccharide vaccine (PPV23), enhances antibody response compared to single PCV dose in patients with inflammatory rheumatic diseases treated with different immunosuppressive drugs and controls. METHODS: Patients receiving rituximab (n = 30), abatacept (n = 23), monotherapy with conventional disease-modifying antirheumatic drugs (cDMARDs, methotrexate/azathioprine/mycophenolate mofetil, n = 27), and controls (n = 28) were immunized with a dose PCV followed by PPV23 after ≥ 8 weeks. Specific antibodies to 12 serotypes included in both vaccines were determined using a multiplex microsphere immunoassay in blood samples before and 4-8 weeks after each vaccination. Positive antibody response was defined as ≥ 2-fold increase from pre- to postvaccination serotype-specific IgG concentration and putative protective level as IgG ≥ 1.3 µg/mL. The number of serotypes with positive antibody response and IgG ≥ 1.3 µg/mL, respectively, after PCV and PCV + PPV23 were compared within each treatment group and to controls. Opsonophagocytic activity (OPA) assay was performed for serotypes 6B and 23F. RESULTS: Compared to single-dose PCV, prime-boost vaccination increased the number of serotypes with positive antibody response in patients with abatacept, cDMARDs, and controls (p = 0.02, p = 0.01, and p = 0.01), but not in patients on rituximab. After PCV + PPV23, the number of serotypes with positive antibody response was significantly lower in all treatment groups compared to controls but lowest in rituximab, followed by the abatacept and cDMARD group (p < 0.001). Compared to PCV alone, the number of serotypes with putative protective levels after PCV + PPV23 increased significantly only in patients in cDMARDs (p = 0.03) and controls (p = 0.001). Rituximab treatment was associated with large reduction (coefficient - 8.6, p < 0.001) and abatacept or cDMARD with moderate reductions (coefficients - 1.9 and - 1.8, p = 0.005, and p < 0.001) in the number of serotypes with positive antibody response to PCV + PPV23 (multivariate linear regression model). OPA was reduced in rituximab (Pn6B and Pn23F, p < 0.001), abatacept (Pn23F, p = 0.02), and cDMARD groups (Pn6B, p = 0.02) compared to controls. CONCLUSIONS: Prime-boost strategy enhances immunogenicity compared to single pneumococcal conjugate vaccination in patients with inflammatory rheumatic diseases receiving cDMARDs, to some extent in abatacept but not in patients on rituximab. Pneumococcal vaccination should be encouraged before the initiation of treatment with rituximab. TRIAL REGISTRATION: ClinicalTrials.gov, NCT03762824. Registered on 4 December 2018, retrospectively registered.

Correction to: Prime-boost vaccination strategy enhances immunogenicity compared to single pneumococcal conjugate vaccination in patients receiving conventional DMARDs, to some extent in abatacept but not in rituximab-treated patients.

An amendment to this paper has been published and can be accessed via the original article.

Newborn Screening for Presymptomatic Diagnosis of Complement and Phagocyte Deficiencies.

The clinical outcomes of primary immunodeficiencies (PIDs) are greatly improved by accurate diagnosis early in life. However, it is not common to consider PIDs before the manifestation of severe clinical symptoms. Including PIDs in the nation-wide newborn screening programs will potentially improve survival and provide better disease management and preventive care in PID patients. This calls for the detection of disease biomarkers in blood and the use of dried blood spot samples, which is a part of routine newborn screening programs worldwide. Here, we developed a newborn screening method based on multiplex protein profiling for parallel diagnosis of 22 innate immunodeficiencies affecting the complement system and respiratory burst function in phagocytosis. The proposed method uses a small fraction of eluted blood from dried blood spots and is applicable for population-scale performance. The diagnosis method is validated through a retrospective screening of immunodeficient patient samples. This diagnostic approach can pave the way for an earlier, more comprehensive and accurate diagnosis of complement and phagocytic disorders, which ultimately lead to a healthy and active life for the PID patients.

Clinical Complement Analysis-An Overview.

The complement system plays an important role in varying types of disease, ranging from inflammatory and autoimmune disorders to immune deficiency states. In addition, new settings have emerged where complement analysis is of interest to monitor complement-directed therapy and aid identification of transplant complications. Therefore, it is critical that clinical laboratories offer optimized and timely complement analysis. This review presents a comprehensive overview of the most important complement analysis methods that are currently used. It also points to some areas within complement diagnostics where development is needed, for example, regarding certain analytes for which practical methods suitable for the routine laboratory are lacking. Furthermore, it contains a more detailed discussion on complement autoantibody assessment. The list of analyses providing clinically valuable information includes analysis of complement function, quantification of individual complement components and complement activation fragments, identification of autoantibodies to complement, as well as genetic complement analyses. There is still a shortage of commercially available methods suitable for high-throughput screening of complement deficiency and for assessment of complement activation, but development is under way. There is also ongoing work within the complement community to improve standardization of measurements, and recently, an extensive quality assurance program has been initiated.

Analysis of C3 Nephritic Factors by ELISA.

Autoantibodies to the C3 convertase of the alternative pathway of complement, called C3 nephritic factors (C3NeF), cause persistently low C3 in the circulation and production of C3 degradation fragments due to prolonged stabilization of the C3 convertase. C3NeF are associated with glomerulopathy, acquired partial lipodystrophy, and less frequently with increased susceptibility to meningococcal infection. Analysis of C3NeF is an important part of the diagnostic workup of C3 glomerulopathy, but their identification is difficult presumably due to considerable heterogeneity. Therefore it is recommended to use a combination of different analysis methods for the detection of C3NeF. Here we present an ELISA method for detection of C3NeF.

Analysis of Anti-C1q Autoantibodies by Western Blot.

Anti-C1q autoantibodies may be found in many conditions, most commonly in systemic lupus erythematosus (SLE) and hypocomplementemic urticarial vasculitis syndrome (HUVS), and are diagnostic markers as well as disease activity markers in lupus nephritis. Sera from patients with SLE and HUVS show partly distinct autoantibody reactivities to separated protein chains B and C of the first component of complement, C1q. These different binding specificities can be detected by Western blot analysis of the autoantibodies under reducing conditions. Results may help clinicians to differentiate between SLE and HUVS.