Normal Serum C3 Research Articles

#1793 Association of low serum complement C3 with reduced renal survival in ANCA associated vasculitis

Abstract Background and Aims ANCA-associated vasculitis (AAV) is a condition that remains poorly understood. Recent data suggest the existence of a complement alternative pathway activation in the pathogenesis of this disease. And recent studies have correlated low complement levels to unfavourable outcomes. Our study aimed to determine whether low serum C3 levels could be used to estimate the severity of AAV and predict renal survival. Method Our study enrolled 26 patients diagnosed with AAV between January 2013 and January 2023. C3 levels were assessed at the time of diagnosis, and patients were categorized into two groups: those with low serum C3 levels and those with normal serum C3 levels (0.9–1.8 g/l). We examined the correlation between serum C3 levels and the severity of AAV at the time of diagnosis, as well as renal survival. Results The average age at diagnosis was 52.5 years, with 15 male patients (57.69%). All patients had kidney involvement, 30% of patients had respiratory symptoms (mostly due to diffuse alveolar hemorrhage) 42% had Ear Nose Throat system involvement 15% had nervous symptoms and 38% had skin signs. The mean Birmingham Vasculitis Activity Score (BVAS) at presentation was 20, and the average serum creatinine level was 360 µmol/l. The mean serum C3 and C4 levels were 108.3 and 24.5 mg/dL, respectively. Forty-two percent of the patients (eleven patients) had a low serum C3 level at presentation. Low C3 level was significantly correlated with poor renal survival (p: 0.031) and relapse after 6 months of immunosuppressive treatment (p: 0.02). Furthermore, remission at 6 months was significantly more frequent in patients with normal C3 levels. Conclusion The assessment of C3 level in AAV can be a valuable tool to predict the disease severity. Hypocomplementemia can predict worse renal outcome. This phenotype may confer a poor response to usual immunosuppressive approaches. Corresponding patients may greatly benefit from complement-targeting therapy.

The Clinical and Pathological Effects of Serum C3 Level and Mesangial C3 Intensity in Patients with IgA Nephropathy.

To investigate the clinical and pathological effects of serum C3 level, mesangial C3 deposition intensity and blood lipid on IgA nephropathy. According to the deposition intensity of immunofluorescence (IF) complement C3 in mesangial region, a total of 151 patients were divided into: (1) negative group (65 cases), (2) weak positive group (51 cases), and (3) strong positive group (35 cases). According to the level of serum C3, the patients were divided into two groups: (1) 33 patients with decreased serum C3 (<85 mg/dL); (2) 118 patients with normal serum C3. The clinicopathological data of the patients were analyzed retrospectively according to the groups. (1) With the increase of C3 deposition in mesangial region, the mean value of serum C3 level decreased, and the difference was statistically significant (P=0.001). (2) Compared with the normal serum C3 group, the blood urea nitrogen (BUN), serum creatinine (Scr), and albumin (Alb) in the serum C3 decreased group were higher, and the differences were statistically significant (P < 0.05), while the fasting blood glucose (FBG), low-density lipoprotein (LDL), triglyceride and 24-hr urinary protein (24hUTP) were lower, which difference was statistically significant (P < 0.05). (3) Compared with negative group and weak positive group, BUN, uric acid (UA), and Scr were higher in the strong positive group with C3 deposition, while eGFR was lower, with statistical significance (P < 0.05). However, C3 deposition in the mesangial region was related to T and enhanced mesangial C3 deposition was associated with more severe tubular atrophy and/or interstitial fibrosis, with statistically significant differences (P=0.001). Patients with strong mesangial C3 deposition and elevated lipid levels had more severe tubule atrophy and/or interstitial fibrosis, as well as more severe pathological lesions, suggesting that activation of the complement system is involved in the pathogenesis of IgA nephropathy and increases the metabolic burden of the kidney.

Association of Low Serum Complement 3 with Worse Glomerular Filtration Rate in Patients with IgA Nephropathy Secondary to Psoriasis

Objective: Complement system is pivotal in the pathogenesis of psoriasis and IgA Nephropathy (IgAN). Few studies have examined the features of patients with IgAN secondary to Psoriasis (IgAN-Pso). The association of serum complement and renal function is unknown. This study was made to investigate the relationship between serum C3 and glomerular filtration rate in patients with IgAN-Pso. Methods: In this retrospective cross-sectional study, eighty-five patients with IgAN without evidence of a secondary cause other than psoriasis were enrolled. Patients were divided into two groups: the serum ≥ 0.9 g/L group (n=56) and the serum <0.9 g/L group (n=29). We used CKD-EPI equation to estimate Glomerular Filtration Rate (eGFR) and Empower Stats software to assess the relationship study. Results: Patients with low serum C3 showed lower eGFR level than those with normal serum C3 (88.7 ml/min/1.73 m2 [57.6-107] and 76.3 ml/min/1.73 m2 [51.2-102]). No statistically differences were found in the histological characteristics between the two groups. Univariate analysis showed a positive correlation between serum C3 and eGFR (β =-26.4, 95%CI: -3.4 to 56.1, P=0.086). After adjusting for confounding factors, the positive correlation between serum C3 and eGFR became statistically significant. The eGFR increased by 7.23 ml/min/1.73 m2 and 7.26 ml/min/1.73 m2 with each increase of 0.1 g/ L of serum C3 in the adjustment II and adjustment III model, respectively. The eGFR in patients with low C3 decreased by 27.8 ml/min/1.73 m2 and 17.2 ml/min/1.73 m2 compared with that in patients with normal C3 levels in the adjustment II and adjustment III model, respectively. Furthermore, curve fitting showed that serum C3 and eGFR had a non-linear positive correlation. Conclusion: Decreased serum C3 was associated with poor renal function in patients with IgAN-Pso, suggesting that complement system could be participated in the pathogenesis of IgAN-Pso.

Predictive Value of Serum Interleukins in Children with Idiopathic Nephrotic Syndrome.

Pro-inflammatory cytokines have been suggested in the pathogenesis of idiopathic nephrotic syndrome (INS), with conflicting results. This study was performed to identify alteration of different serum interleukins (ILs) in children with INS, and their predictive value in response to steroid treatment. Three groups of children (27; steroid-sensitive INS, 21; steroid-resistant INS, and 19 healthy controls) with normal serum C3, negative serologic tests of hepatitis B virus (HBV), hepatitis C virus (HCV), human immune deficiency virus (HIV), and parasitic infections were included in this study. Serum concentrations of IL-1β, IL-2, IL-6, IL-8, IL-13, and IL-18 were measured, using quantitative colorimetric sandwich ELISA kits. Children with secondary nephrotic syndrome, inflammations, systemic disorders, and chronic kidney disease were excluded. The serum concentration of all ILs; except IL-13 and IL-18; was significantly higher in children with INS, compared with the healthy controls. Serum IL-2 had the highest sensitivity of (95.24%) in patients with INS. All of the serum ILs had acceptable accuracy in children with INS, compared with the control group. The serum concentration of IL-1β, IL-6, and IL-8 was significantly higher in children with steroid-sensitive nephrotic syndrome (SSNS), compared with steroid-resistant nephrotic syndrome (SRNS). All of these ILs had acceptable accuracy for the prediction of steroid response in patients with INS. Our findings suggested the pathogenic role of pro-inflammatory cytokines in children with INS, of which IL-1β, IL-6, and IL-8 were accurate biomarkers for the prediction of steroid response in these patients.

Serum C3 complement levels in ANCA associated vasculitis at diagnosis is a predictor of patient and renal outcome.

To determinate the prognostic significance of low serum C3 at the time of diagnosis of ANCA-associated vasculitis (AAV). Our cohort included 75 consecutive patients with AAV diagnosed from January 2005 to December 2015. C3 levels were measured at the time of diagnosis. Patients were divided into two groups, those with low serum C3 levels (< 0.9g/l) and those with normal serum C3 levels (0.9-1.8g/l). We analysed association between serum C3 levels and both combined and singularly patient and renal survival (ESRD). Small number of relapsed patients did not allow for the statistical analysis to be performed as to weather the low serum C3 is associated with relapse rate in AAV patients. Low serum C3 levels were significantly associated with worse combined end-point patient and renal survival (HR 3.079; 95% CI 1.231-7.701; p = 0.016), and on multivariate adjusted analysis association remained significant (HR 2.831; 95% CI 1.093-7.338; p = 0.032). For both end-points individually low serum C3 levels were significantly associated with poorer patient survival (HR 6.378; 95% CI 2.252-18.065; p < 0.001; on multivariate adjusted analysis HR 4.315 95% CI 1.350-13.799; p = 0.014) and renal survival (HR 3.207; 95% CI 1.040-9.830; p = 0.043; on multivariate adjusted analysis HR 3.679; 95% CI 1.144-11.827; p = 0.029). In our study there was no significant association between serological and patohistological phenotypes and serum C3 levels. Lower serum C3 levels at the diagnosis is associated with poorer patient and renal outcomes in AAV patients.

Death Related to Ibuprofen, Valdecoxib, and Medical Errors

Death Related to Ibuprofen, Valdecoxib, and Medical Errors

Atypical hemolytic uremic syndrome in children: complement mutations and clinical characteristics

BackgroundMutations in complement factor H (CFH), factor I (CFI), factor B (CFB), thrombomodulin (THBD), C3 and membrane cofactor protein (MCP), and autoantibodies against factor H (αFH) with or without a homozygous deletion in CFH-related protein 1 and 3 (∆CFHR1/3) predispose development of atypical hemolytic uremic syndrome (aHUS).MethodsDifferent mutations in genes encoding complement proteins in 45 pediatric aHUS patients were retrospectively linked with clinical features, treatment, and outcome.ResultsIn 47% of the study participants, potentially pathogenic genetic anomalies were found (5xCFH, 4xMCP, and 4xC3, 3xCFI, 2xCFB, 6xαFH, of which five had ∆CFHR1/3); four patients carried combined genetic defects or a mutation, together with αFH. In the majority (87%), disease onset was preceeded by a triggering event; in 25% of cases diarrhea was the presenting symptom. More than 50% had normal serum C3 levels at presentation. Relapses were seen in half of the patients, and there was renal graft failure in all except one case following transplant.ConclusionsPerforming adequate DNA analysis is essential for treatment and positive outcome in children with aHUS. The impact of intensive initial therapy and renal replacement therapy, as well as the high risk of recurrence of aHUS in renal transplant, warrants further understanding of the pathogenesis, which will lead to better treatment options.

Nephrotic syndrome presenting in a patient with primary Sjögren’s syndrome: questions

Case summary A 17 year-old African American woman with a history of Sjogren’s syndrome presented with several days of periorbital and pedal edema. She also had fatigue, headache, abdominal pain, and diffuse arthralgias. She had no gross hematuria or oliguria. There were no recent sore throats or upper respiratory tract infections. She had no weight loss, night sweats, joint swelling, oral ulcerations, or rash. She had taken several doses of ibuprofen for arthralgias but was not taking any other medications. She was diagnosed with primary Sjogren’s syndrome at 11 years of age after presenting with bilateral parotitis. The diagnosis of Sjogren’s syndrome was based on the parotitis and a history of xerostomia and xerophthalmia. Schirmer’s test was abnormal (prolonged wetting time of filter paper placed in the lower eyelid), indicating abnormal tear production. Sialometry showed inadequate saliva production. Serologic markers at the time of diagnosis of Sjogren’s syndrome included normal serum C3 and C4, elevated antinuclear antibodies (ANA) of 1:2560, elevated anti-Ro/SSA antibody, negative anti-double-stranded DNA antibody, and elevated rheumatoid factor. She had a normal serum creatinine concentration of 0.7 mg/dl and a normal urinalysis with no blood or protein. She was treated with prednisone for 1 year and remained symptom free aside from intermittent mild xerostomia and xerophthalmia. Her father has systemic lupus erythematosus (SLE) and lupus nephritis.

Human C3 Deficiency Associated with Impairments in Dendritic Cell Differentiation, Memory B Cells, and Regulatory T Cells

Primary C3 deficiency, a rare autosomal inherited disease (OMIM 120700), was identified in a 2-year-old male suffering from recurrent pyogenic infections from early infancy with undetectable total complement hemolytic activity (CH50) and C3 values. The nonconsanguineous parents and the two patients' two siblings had 50% normal serum C3 concentration. The molecular abnormality associated a paternal allele coding C3 with the missense mutation p.Ser(550)Pro and an apparently null maternal allele, with production of a defective protein that could no longer be secreted. Vaccination of the child did not induce a long-term Ab response. Accordingly, switched memory IgD(-)CD27(+) B cells were barely detected, amounting to only 2.3% of peripheral blood CD19(+) cells. Cells were significantly defective in stimulating alloreactive responses. The in vitro development of immature dendritic cells and their maturation capacity were greatly impaired, with decreased CD1a expression and IL-12p70 secretion ability. These cells were unable to induce autologous B cell proliferation and Ig secretion in the presence of CD40L and C3. Finally, the regulatory T cell development ability of CD4(+) T cells after CD3 and CD46 activation in the presence of IL-2 was significantly impaired. Thus, the association of important functional defects of dendritic cells, acquisition of B cell memory, and regulatory T cells with human C3 deficiency strongly supports a major role for C3 in bridging innate and adaptive immunity in humans.

Detection of two variants of complement component C3 in C3-deficient guinea pigs distinguished by the absence and presence of a thiolester

The complement system is an essential part of the innate defense, and C3 is an integral part of this powerful system. In previously identified complement C3 deficient guinea pigs only approx. 5% of the normal serum C3 level is detectable. No differences were found between in vitro C3 protein synthesis and C3 mRNA levels of cells from C3-deficient and wild-type animals and the amino acid sequences of both C3 proteins are identical as deduced from cDNA sequencing. Previously, the principal inability to form a C3 thiolester was discussed as a possible reason for this C3-deficiency. Here we report the isolation of two functionally different C3 species from the C3-deficient animals. Only one of these C3 proteins exhibits normal hemolytic activity and contains a thiolester group. The second C3 species is exclusively present in C3-deficient animals and lacks a thiolester, explaining its failure to express hemolytic activity. The presence of a second C3 species lacking a thiolester structure only in C3-deficient animals indicates that the stability of the thiolester may play a role in C3 deficiency. However further analysis of the in vitro stability of the thiolesters of C3 from normal and C3-deficient guinea pigs revealed no differences. A decreased in vivo thiolester stability might lead to the presence of C3 with and without a thiolester or alternatively the expression of two isoforms of C3 in these animals. Considering the central role of C3 in host defense, the mechanisms of C3 thiolester formation require further analysis.

The third component of complement protects against Escherichia coli endotoxin-induced shock and multiple organ failure.

We investigated whether the third component of complement (C3) is involved in the pathophysiology of endotoxic shock, and if it is involved, whether it plays a protective role or whether it mediates shock and multiple organ failure. In a prospective, controlled investigation, six Brittany spaniels that were homozygous for a genetically determined deficiency of C3 (C3 deficient, < 0.003% of normal serum C3 levels) and six heterozygous littermates (controls, approximately 50% of mean normal serum C3 level) were given 2 mg/kg of reconstituted Escherichia coli 026:B6 acetone powder as a source of endotoxin, intravenously. All animals were given similar fluid and prophylactic antibiotic therapy, and had serial hemodynamic variables obtained. After E. coli endotoxin infusion, C3-deficient animals had higher peak levels of endotoxin and less of a rise in temperature than controls (P < 0.05). During the first 4 h after E. coli endotoxin infusion, C3-deficient animals had significantly greater decreases in mean central venous pressure and mean pulmonary artery pressure than controls (P < 0.02). During the first 48 h after E. coli endotoxin infusion, C3-deficient animals had significantly greater decreases in mean arterial pH, left ventricular ejection fraction, and mean pulmonary capillary wedge pressure, and greater increases in mean arterial lactate, arterial-alveolar O2 gradient, and transaminases (aspartate aminotransferase and alanine aminotransferase) than controls, (all P < 0.05). After E. coli endotoxin infusion, C3-deficient animals compared to controls had significantly less of a decrease in mean C5 levels (P < 0.01), but similar (P = NS) increases in circulating tumor necrosis factor levels, bronchoalveolar lavage neutrophils, and protein, and similar (P = NS) decreases in blood leukocytes and platelets. Two of six C3-deficient animals and two of six controls died. In summary, after intravenous infusion of E. coli endotoxin, canines with C3 deficiency have decreased endotoxin clearance and worse E. coli endotoxin-induced shock and organ damage. Thus, the third component of the complement system plays a beneficial role in the host defense against E. coli endotoxic shock.

Interaction of human CR1, CR2, and h with expressed C3 and chimeric C3 molecules

The complement system is an essential part of the innate defense, and C3 is an integral part of this powerful system. In previously identified complement C3 deficient guinea pigs only approx. 5% of the normal serum C3 level is detectable. No differences were found between in vitro C3 protein synthesis and C3 mRNA levels of cells from C3-deficient and wild-type animals and the amino acid sequences of both C3 proteins are identical as deduced from cDNA sequencing. Previously, the principal inability to form a C3 thiolester was discussed as a possible reason for this C3-deficiency. Here we report the isolation of two functionally different C3 species from the C3-deficient animals. Only one of these C3 proteins exhibits normal hemolytic activity and contains a thiolester group. The second C3 species is exclusively present in C3-deficient animals and lacks a thiolester, explaining its failure to express hemolytic activity. The presence of a second C3 species lacking a thiolester structure only in C3-deficient animals indicates that the stability of the thiolester may play a role in C3 deficiency. However further analysis of the in vitro stability of the thiolesters of C3 from normal and C3-deficient guinea pigs revealed no differences. A decreased in vivo thiolester stability might lead to the presence of C3 with and without a thiolester or alternatively the expression of two isoforms of C3 in these animals. Considering the central role of C3 in host defense, the mechanisms of C3 thiolester formation require further analysis.

C3-like activity in C3-deficient dog serum.

A complete absence of the third component of complement has been demonstrated in a colony of Brittany spaniels. The deficiency is inherited in an autosomal recessive fashion and is clinically characterized by an increased susceptibility to infection and renal disease. Despite having no detectable antigenic C3, C3-deficient dog serum has approximately 10% of normal serum C3 hemolytic activity. This report characterizes the nature of the C3-like activity in C3-deficient dog serum. The activity is inhibited by heating serum to 56 degrees C for 30 min and by incubation in 0.01 M EDTA. The activity is also sensitive to both methylamine and D-76, in a dose-dependent fashion. The lytic activity in C3-deficient dog serum appears to be complement mediated. Furthermore, lysis of EAC1,4,oxy2 cells by deficient dog serum is inhibited by methylamine. Although lysis is boosted by the addition of purified C5, a greater boost is obtained in the absence of methylamine. Therefore, there exists a methylamine-sensitive protein other than C4 in C3-deficient dog serum which interacts with C5. It is possible that this protein may be a newly discovered complement protein for which appropriate conditions for its detection have not previously been available.

Impaired humoral immune response in complement C3-deficient guinea pigs: absence of secondary antibody response.

A recently described genetically controlled C3 deficiency (C3D) in guinea pigs (GP) provided a unique model for studying the role of C3 in the afferent limb of the humoral immune response in a direct manner. These C3D animals, which have only 5-7% of normal serum C3 level, were immunized with the bacteriophage phi chi 174, a T cell-dependent antigen, followed by a booster injection after 4 weeks (1.5 X 10(9) plaque-forming units/kg). The formation of IgM and IgG antibody in the course of the primary and secondary response was determined and compared with a control group of inbred strain 2 GP. The C3D animals showed a markedly diminished antibody response to this antigen. Amplification of the antibody titer as well as regular isotype switching from IgM to IgG was absent in the secondary response. Increasing the amount of antigen to a high dose (1 X 10(10) plaque-forming units/kg) led to a normalization of the antibody response. The impairment in antibody formation resembles closely the impaired antibody response in C4-deficient or C2-deficient GP, which both have a block in activation of C3 via the classical pathway. However, in contrast to C4D GP or C2D GP the C3D GP do not exhibit serological characteristics of immune complex disease. They have normal levels of total serum IgM, of IgM anti-2,4-dinitrophenyl antibodies and of IgM rheumatoid factors.

Complement interaction with immune serum globulin and immune globulin intravenous

Three complement assays, C1q binding activity, C3 activation in normal human serum, and enhancement of alternative pathway activity, have been used to evaluate the in vitro anticomplementary activity of untreated and heat-aggregated (63 °C, 10 minutes) immune serum globulin and immune globulin intravenous prepared by partial reduction and alkylation. Unheated immune globulin intravenous marginally activated endogenous C3 in normal serum, had a fivefold lower affinity for 125I C1q but was very similar to immune serum globulin in enhancing complement alternative pathway activity. Heat-aggregated immune globulin intravenous was about twofold less effective than heat-aggregated immune serum globulin in the activation of C3 in normal serum and had approximately a threefold lower affinity for 125I C1q. The ability of immune globulin intravenous to retain specific complement receptor activity suggests that it would also retain in vivo efficacy in complement-mediated amplification of host defense reactions but that it is safe for intravenous use due to a lower capacity to initiate nonspecific complement activation.

The interaction of immune serum globulin and immune globulin intravenous with complement

The in vitro anticomplementary activity of untreated and heat-aggregated (63°C, 10 min) immune serum globulin (ISG) and immune globulin intravenous (IGIV) prepared by partial reduction and alkylation have been evaluated by three assays, C3 activation, binding to Clq and enhancement of alternative pathway lysis of rabbit erythrocytes. Crossed immunoelectrophoresis was used to quantitatively measure the ability of ISG and IGIV to activate endogenous C3 in normal serum. Binding to Clq was determined according to the ability to inhibit binding of 125I-Clq to solid phase IgG. ISG and IGIV enhancement of lysis of rabbit erythrocytes by normal human serum adsorbed with rabbit erythrocytes in the presence of MgEGTA was used to determine activity in the alternative complement pathway. Unheated IGIV at 10mg/ml only marginally activated endogenous C3 in normal serum, had about a 5-fold lower affinity for 125I-Clq ( K i = 138 to 356 μM vs K i = 62.5 μM for ISG), but was very similar in ability to ISG on a weight basis in enhancing complement alternative pathway activity ( RCH50 = 0.23 to 0.40 mg for IGIV vs 0.17mg for ISG). Heat-aggregated IGIV at 5 mg/ml in normal human serum was about 2-fold less effective than heat-aggregated ISG in the activation of C3 in normal serum and had approximately 2- to 3-fold lower affinity in the Clq binding assay ( K i = 45 to 83 n M for heat-aggregated IGIV vs K i = 14.6 n M for heat-aggregated ISG). These data suggest that IGIV prepared by chemical modification retains sufficient specific receptor activity to allow in vivo efficacy in complement-mediated amplification of host defense reactions, but is safe for intravenous use due to a lower capacity to initiate nonspecific complement activation.

Biosynthesis of the third component of complement (C3) in vitro by monocytes from both normal and homozygous C3-deficient humans.

Human monocytes synthesized the third component of complement (C3) up to 5 wk in vitro. Evidence for net C3 synthesis was based on (a) incorporation of 14C-labeled amino acids into C3 protein, (b) indentity of the allotype of C3 produced in vitro with that of the doner's serum C3, even in the presence of carrier C3 protein of a different allotype; (c) correspondence of electrophoretic mobility, size, and subunit structure of C3 protein produced in vitro with serum C3; (d) inhibition of C3 production with cycloheximide. Monocytes from two unrelated C3-deficient patients were studied under conditions that supported C3 synthesis by normal monocytes. Serum from each of the patients contained less than 1% of the normal C3 concentration, buth their monocytes produced C3 at approximately equal to 25% of the normal rate when studied after 2 wk in vitro. The C3 produced in vitro by monocytes from one of the patients had the molecular weight of normal serum C3 and dissociated appropriately under reducing conditions. Monocytes from C3-deficient patients could not be distinguished from normals on the basis of morphology, rosetting with C3-coated erythrocytes, or rates of C2, and total protein synthesis.

ALTERNATIVE COMPLEMENT PATHWAY (AP) IN CHILDREN WITH NEPHROSIS (CN)

In surveying the AP in children, 7 CN with normal serum C3 but low-normal or low-Factor B were studied. Heavy proteinuria was found in all, impaired renal function in 2. Two received daily and 2 alternate day prednisone. Renal biopsy revealed minimal changes in 2, mesangial nephritis in 2; focal, post-strep and congenital nephritis in one each. C3, C4, C5, B, properdin (P), and B1H were measured by radial immunodiffusion. C function was evaluated by lysis of EA (CH50) or EAC142 in the presence of EDTA (C3--9), lysis of glutathione-treated human E (APLys) and C3 and B conversion on immunoelectrophoresis in fresh serum and following 37°C incubation with buffer or inulin (C3-B/C). All data were compared to age-matched normal children.B correlated with APLys, not so well with P, and not at all with B1H or C3-B/C. B was found in concentrated urine specimens of 2 with low-normal serum B. Classical C activation was present only in post-strep nephritis. Low B levels cannot be explained simply by urinary loss or consumptive depletion, and may reflect depressed synthesis. The relationship of normal C3 to low B remains to be explored, but our data clearly emphasize the importance of age-matched controls in evaluating the AP in children.

MONOCYTES FROM PATIENTS WITH GENETIC DEFICIENCY OF THE THIRD COMPONENT OF COMPLEMENT (C3) PRODUCE C3 IN VITRO

A method has been described for maintenance of human monocytes in culture for up to six months. The cells synthesize and secrete the second (C2) and third (C3) components of complement and lysozyme, phagocytose latex beads, rosette with IgG or C3 coated erythrocytea, and kill L. monocytogenes. Monocytes from two unrelated C3 deficient patients, one of whom has been described (J. Clin. Invest. 56, 703, 1975), were examined in culture. Serum from each of the patients contained less than 1% of the normal C3 concentration (not due to hypercatabolism) but monocytes from each produced C3 at approximately 25% of the normal rate when studied after two weeks in vitro. The C3 produced in vitro by monocytes from one of the patients was shown to have the molecular weight of normal serum C3 and to dissociate appropriately under reducing conditions. Monocytes from C3 deficient patients could not be distinguished from normals on the basis of morphology, resetting with C3 coated erythrocytes, or rates of C2 and total protein synthesis. The ability of monocytes from C3 deficient patients to produce C3 in vitro is in contrast to studies of monocytes from C2 deficient humans and macrophages from C4 deficient guinea pigs in which specific biosynthetic defects for C2 and C4, respectively, persisted in vitro.

C3 Nephritic Factor (C3NeF): Stabilization of Fluid Phase and Cell-Bound Alternative Pathway Convertase

C3 nephritic factor (C3NeF) defined by the capacity of nephritic serum and its fractions to initiate loss of the B antigen of C3 in normal serum was purified from the serum of three different donors and shown to function by stabilization of membrane-bound and fluid phase alternative pathway C3 convertase. C3NeF converts cell-bound C3B sites in a dose-related manner to CEB(NeF) sites, which exhibit an approximate 10-fold increase in half-life. The linear relationship between the C3NeF input and the residual hemolytic sites on EAC43B present after incubation for 20 min at 30 degrees C, during which labile C3B sites have decayed, indicates that the number of residual C3B sites is directly related to the dose of C3NeF. The capacity of C3NeF to stabilize the C3B convertase in a temperature- and dose-dependent manner, which is independent of binding or consumption of C3NeF, in a fluid phase reaction mixture of 125I-B, 131I-C3 and D permits isolation of a 10S complex containing radiolabeled C3 and B and exhibiting C3, convertase activity on an exogenous C3 source. Thus, the stabilizing effect of C3NeF is not limited to membrane-bound C3B but is also sufficient to permit recovery of a fluid phase C3 convertase formed during the interaction of C3, B, and D.