Dissecting the impact of complement component 4A in bipolar disorder

The genetic overlap between schizophrenia (SZ) and bipolar disorder (BD) is substantial. Polygenic risk scores have been shown to dissect different symptom dimensions within and across these two disorders. Here, we focused on the most strongly associated SZ risk locus located in the extended MHC region, which is largely explained by copy numbers of the gene coding for complement component 4A (C4A). First, we utilized existing brain tissue collections (N = 1,202 samples) and observed no altered C4A expression in BD samples. The generated C4A seeded co-expression networks displayed no genetic enrichment for BD. To study if genetically predicted C4A expression discriminates between subphenotypes of BD, we applied C4A expression scores to symptom dimensions in a total of 4,739 BD cases with deep phenotypic data. We identified a significant association between C4A expression and psychotic mood episodes in BD type 1 (BDI). No significant association was observed between C4A expression and the occurrence of non-affective psychotic episodes in BDI, the psychosis dimensions in the total BD sample, or any other subphenotype of BD. Overall, these results points to a distinct role of C4A in BD that is restricted to vulnerability for developing psychotic symptoms during mood episodes in BDI.

Complement C4-A and Plasminogen as Potential Biomarkers for Prediction of Papillary Thyroid Carcinoma

BACKGROUND

Early diagnosis and therapy of papillary thyroid carcinoma (PTC) is essential for reducing recurrence and improving the long-term survival. In this study, we aimed to investigate the proteome profile of plasma and screen unique proteins which could be used as a biomarker for predicting PTC.

METHODS

Serum samples were collected from 29 PTC patients and 29 nodular goiter (NG) patients. Five PTC serum samples and five NG serum samples were selected for proteome profiles by proteomics. Eight proteins in PTC and NG serum samples were selected for confirmation by enzyme-linked immunosorbent assay analysis. Receiver operating characteristic curves was used to evaluate the diagnostic value of potential biomarkers.

RESULTS

Complement C4-A (C4A) and plasminogen (PLG) were significantly lower in serum samples of PTC patients compared with NG patients. C4A was observed to have excellent diagnostic accuracy for PTC, with a sensitivity of 91.67% and specificity of 83.33%. The diagnostic value of PLG for PTC was demonstrated by a sensitivity at 87.50% and specificity at 75.00%. The AUC for C4A and PLG was 0.97 ± 0.02 and 0.89 ± 0.05.

CONCLUSION

C4A and PLG appeared to be excellent potential biomarkers for the prediction of PTC.

Complement C4A Regulates Autoreactive B Cells in Murine Lupus

Systemic lupus erythematosus (SLE) is a severe autoimmune disease mediated by pathogenic autoantibodies. While complement protein C4 is associated with SLE, its isoforms (C4A and C4B) are not equal in their impact. Despite being 99% homologous, genetic studies identified C4A as more protective than C4B. By generating gene-edited mouse strains expressing either human C4A or C4B and crossing these with the 564lgi lupus strain, we show that, overall, C4A-like 564Igi mice develop less humoral autoimmunity than C4B-like 564Igi mice. This includes a decrease in the number of GCs, autoreactive B cells, autoantibodies, and memory B cells. The higher efficiency of C4A in inducing self-antigen clearance is associated with the follicular exclusion of autoreactive B cells. These results explain how the C4A isoform is protective in lupus and suggest C4A as a possible replacement therapy in lupus.

Simoni et al. address a long-standing question about how complement C4A and C4B isoforms differ in function in vivo in autoimmunity. They find that C4A leads to an increased protection in humoral autoimmunity relative to C4B. Autoantibody diversity is likewise dependent on the C4 protein isotype.

Genetically predicted complement component 4A expression: effects on memory function and middle temporal lobe activation

BACKGROUND

The longstanding association between the major histocompatibility complex (MHC) locus and schizophrenia (SZ) risk has recently been accounted for, partially, by structural variation at the complement component 4 (C4) gene. This structural variation generates varying levels of C4 RNA expression, and genetic information from the MHC region can now be used to predict C4 RNA expression in the brain. Increased predicted C4A RNA expression is associated with the risk of SZ, and C4 is reported to influence synaptic pruning in animal models.

METHODS

Based on our previous studies associating MHC SZ risk variants with poorer memory performance, we tested whether increased predicted C4A RNA expression was associated with reduced memory function in a large (n = 1238) dataset of psychosis cases and healthy participants, and with altered task-dependent cortical activation in a subset of these samples.

RESULTS

We observed that increased predicted C4A RNA expression predicted poorer performance on measures of memory recall (p = 0.016, corrected). Furthermore, in healthy participants, we found that increased predicted C4A RNA expression was associated with a pattern of reduced cortical activity in middle temporal cortex during a measure of visual processing (p < 0.05, corrected).

CONCLUSIONS

These data suggest that the effects of C4 on cognition were observable at both a cortical and behavioural level, and may represent one mechanism by which illness risk is mediated. As such, deficits in learning and memory may represent a therapeutic target for new molecular developments aimed at altering C4's developmental role.

Effects of a Carob-Pod-Derived Sweetener on Glucose Metabolism

BACKGROUND

Patients with type 2 diabetes mellitus (T2DM) have a higher incidence of cardiovascular (CV) events. The ingestion of high-glycemic index (GI) diets, specially sweetened beverage consumption, has been associated with the development of T2DM and CV disease.

OBJECTIVE

We investigated the effects of the intake of a sweetened beverage, obtained from natural carbohydrates containing pinitol (PEB) compared to a sucrose-enriched beverage (SEB) in the context of impaired glucose tolerance (IGT) and diabetes.

METHODS

The study was divided in three different phases: (1) a discovery phase where the plasma proteomic profile was investigated by 2-DE (two-dimensional electrophoresis) followed by mass spectrometry (matrix-assisted laser desorption/ionization time-of-flight-MALDI-TOF/TOF) in healthy and IGT volunteers; (2) a verification phase where the potential mechanisms behind the observed protein changes were investigated in the discovery cohort and in an additional group of T2DM volunteers; and (3) the results were validated in a proof-of-concept interventional study in an animal model of diabetic rats with complementary methodologies.

RESULTS

Six weeks of pinitol-enriched beverage (PEB) intake induced a significant increase in two proteins involved in the insulin secretion pathway, insulin-like growth factor acid labile subunit (IGF1BP-ALS; 1.3-fold increase; P = 0.200) and complement C4A (1.83-fold increase; P = 0.007) in IGT subjects but not in healthy volunteers. Changes in C4A were also found in the serum samples of Zucker diabetic fatty (ZDF) rats after four weeks of PEB intake compared to basal levels (P = 0.042). In addition, an increased expression of the glucose transporter-2 (GLUT2) gene was observed in the jejunum (P = 0.003) of inositol-supplemented rats when compared to sucrose supplementation. This change was correlated with the observed change in C4A (P = 0.002).

CONCLUSIONS

Our results suggest that the substitution of a common sugar source, such as sucrose, by a naturally-based, pinitol-enriched beverage induces changes in the insulin secretion pathway that could help to reduce blood glucose levels by protecting β-cells and by stimulating the insulin secretion pathway. This mechanism of action could have a relevant role in the prevention of insulin resistance and diabetes progression.

CD66b Overexpression and Loss of C5a Receptors as Surface Markers for Staphylococcus aureus-Induced Neutrophil Dysfunction

Neutrophil granulocytes constitute the main component of innate immunity in the clearance of bacterial infections. However, during systemic inflammation, immunoparalysis may occur resulting in neutrophil dysfunction. This study presents a new in vitro model for analyzing the dysfunction of human peripheral blood neutrophils resulting from the interaction with Staphylococcus aureus components in whole blood. After induction of a massive complement activation by S. aureus supernatant, the neutrophils exhibit a reduced phagocytic capacity resulting in a dramatic reduction of the antibacterial activity similar to that of neutrophils isolated from septic patients. The number of phagocytozing neutrophils is drastically reduced as well as the phagocytic capacity designated by a significantly lower number of ingested microbes. This dysfunction correlates with the loss of complement component 5a receptor 1 from the neutrophil cell surface and can be further characterized by a C5a-induced CD66b overexpression. The presented in vitro model offers a new platform for preclinical testing of immunosuppressive drugs and delivers new information for the understanding of neutrophil dysfunctions under the conditions described.

Development of biomarkers for screening hepatocellular carcinoma using global data mining and multiple reaction monitoring

Hepatocellular carcinoma (HCC) is one of the most common and aggressive cancers and is associated with a poor survival rate. Clinically, the level of alpha-fetoprotein (AFP) has been used as a biomarker for the diagnosis of HCC. The discovery of useful biomarkers for HCC, focused solely on the proteome, has been difficult; thus, wide-ranging global data mining of genomic and proteomic databases from previous reports would be valuable in screening biomarker candidates. Further, multiple reaction monitoring (MRM), based on triple quadrupole mass spectrometry, has been effective with regard to high-throughput verification, complementing antibody-based verification pipelines. In this study, global data mining was performed using 5 types of HCC data to screen for candidate biomarker proteins: cDNA microarray, copy number variation, somatic mutation, epigenetic, and quantitative proteomics data. Next, we applied MRM to verify HCC candidate biomarkers in individual serum samples from 3 groups: a healthy control group, patients who have been diagnosed with HCC (Before HCC treatment group), and HCC patients who underwent locoregional therapy (After HCC treatment group). After determining the relative quantities of the candidate proteins by MRM, we compared their expression levels between the 3 groups, identifying 4 potential biomarkers: the actin-binding protein anillin (ANLN), filamin-B (FLNB), complementary C4-A (C4A), and AFP. The combination of 2 markers (ANLN, FLNB) improved the discrimination of the before HCC treatment group from the healthy control group compared with AFP. We conclude that the combination of global data mining and MRM verification enhances the screening and verification of potential HCC biomarkers. This efficacious integrative strategy is applicable to the development of markers for cancer and other diseases.

Novel potential interacting partners of fibronectin in spontaneous animal model of interstitial cystitis

Feline idiopathic cystitis (FIC) is the only spontaneous animal model for human interstitial cystitis (IC), as both possess a distinctive chronical and relapsing character. Underlying pathomechanisms of both diseases are not clearly established yet. We recently detected increased urine fibronectin levels in FIC cases. The purpose of this study was to gain further insight into the pathogenesis by assessing interacting partners of fibronectin in urine of FIC affected cats. Several candidate proteins were identified via immunoprecipitation and mass spectrometry. Considerable changes in FIC conditions compared to physiological expression of co-purified proteins were detected by Western blot and immunohistochemistry. Compared to controls, complement C4a and thioredoxin were present in higher levels in urine of FIC patients whereas loss of signal intensity was detected in FIC affected tissue. Galectin-7 was exclusively detected in urine of FIC cats, pointing to an important role of this molecule in FIC pathogenesis. Moderate physiological signal intensity of galectin-7 in transitional epithelium shifted to distinct expression in transitional epithelium under pathophysiological conditions. I-FABP expression was reduced in urine and urinary bladder tissue of FIC cats. Additionally, transduction molecules of thioredoxin, NF-κB p65 and p38 MAPK, were examined. In FIC affected tissue, colocalization of thioredoxin and NF-κB p65 could be demonstrated compared to absent coexpression of thioredoxin and p38 MAPK. These considerable changes in expression level and pattern point to an important role for co-purified proteins of fibronectin and thioredoxin-regulated signal transduction pathways in FIC pathogenesis. These results could provide a promising starting point for novel therapeutic approaches in the future.

Functional annotation of the human fat cell secretome

CONTEXT

Recent secretome analyses suggest that human fat cells secrete hundreds of proteins (adipokines).

OBJECTIVE

We made an overall analysis of their potential functional importance.

MATERIALS AND METHODS

A secretome of 347 adipokines was evaluated by in silico analysis of their expression during adipocyte differentiation, regulation by obesity and adipose region. The gene expression in human adipose tissue was investigated in microarray studies using samples from different adipose depots from lean or obese patients.

RESULTS

60% of the adipokines were regulated by obesity and 50% between visceral and subcutaneous adipose region. Eight adipokines, all novel, scored particularly high in the in silico analysis. Among those, four were both regulated by obesity and adipose region, namely WNT1-inducible-signaling pathway protein 2, transmembrane glycoprotein NMB, inter-alpha-trypsin inhibitor heavy chain H5, and complement C4-A. Furthermore, many adipokines were extracellular matrix proteins.

CONCLUSION

Several novel adipokines have potential important functional features warranting in depth analysis.

Lower circulating levels of complement split proteins C3a and C4a in maternal plasma of women with gestational diabetes mellitus

AIM

The aim of this study was to determine the effect of gestational diabetes mellitus on maternal circulating levels of C3a, C4a and C5a.

METHODS

Anaphylatoxin C3a, C4a and C5a levels were measured in maternal and cord plasma from 42 women with normal glucose tolerance and 40 women with gestational diabetes at the time of term elective Caesarean section. Maternal plasma C3a, C4a and C5a concentrations were determined by enzyme-linked immunoassay.

RESULTS

Maternal C3a and C4a concentrations were significantly lower in women with gestational diabetes compared with women with normal glucose tolerance at the time of term delivery (P < 0.05, Student's t-test). There was, however, no difference in maternal circulating C5a levels between the two groups. Additionally, there was no difference in C3a, C4a and C5a levels in cord plasma obtained from women with normal glucose tolerance and those with gesational diabetes. However, a significant positive correlation was observed between maternal and cord complement split levels.

CONCLUSIONS

Gestational diabetes is characterized by lower levels of C3a and C4a in the maternal circulation at the time of term Caesarean delivery.

[Time course of C4a and platelet aggregation rates in no-reflow patients with acute myocardial infarction undergoing percutaneous coronary intervention]

OBJECTIVE

To observe serum C4a and platelet aggregation rates changes in acute myocardial infarction (AMI) patients before and after percutaneous coronary intervention (PCI) and association with the development of no-reflow phenomenon.

METHODS

From June 2006 to August 2009, 119 AMI patients underwent PCI (28 cases of no-reflow group, 91 cases of reflow group) and 30 subjects with suspected coronary heart diseases and normal coronary angiography results (control group) were enrolled in this study. C4a and platelet aggregation rate were measured at 30 minutes before PCI, immediately after PCI, 30 minutes, 1 hour, 2 hour, and 6 months post PCI in AMI patients and at before coronary angiography in control subjects.

RESULTS

The levels of serum C4a at 30 minutes prior to PCI in control, no-reflow, and reflow groups were similar (P > 0.05). Platelet aggregation rate at 30 minutes prior to PCI was significantly higher in no-reflow group and reflow group than in control group (all P < 0.05). Serum C4a and platelet aggregation rates were significantly higher in no-reflow group at immediate, 30 minutes and 1 hour after PCI than at 30 minutes prior to PCI, two hours and 6 months after PCI (all P < 0.05), and were significantly higher than in reflow group at immediate, 30 minutes and 1 hour after PCI (all P < 0.05). Serum C4a and platelet aggregation rates were similar at different time points in reflow group (all P > 0.05). The levels of C4a in no-reflow group at immediate, 30 minutes and 1 hour after PCI were positively correlated with platelet aggregation rates (r = 0.91, 0.79, 0.60, respectively, all P < 0.01).

CONCLUSION

The transient increase on levels of C4a and platelet aggregation rate early post PCI are verified in no-reflow patients with AMI undergoing PCI.

Increased complement consumption in MuSK-antibody-positive myasthenia gravis patients

OBJECTIVE

To investigate the activation of different complement pathways in myasthenia gravis (MG) subtypes.

SUBJECTS AND METHODS

Levels of complement breakdown products for different complement pathways were measured using ELISA in sera of acetylcholine receptor antibody (AChR-Ab)-positive (n = 21), muscle-specific receptor tyrosine kinase (MuSK)-Ab-positive (n = 23) and seronegative generalized MG patients (n = 21) and healthy controls (n = 22). Levels of factor Bb (FBb), the breakdown product of factor B, and C4d, the breakdown product of C4, were measured to evaluate the activity of the alternative and classical complement pathways, respectively. Serum iC3b levels were analyzed to assess total complement activity. The results were expressed as OD values.

RESULTS

MuSK-Ab-positive MG patients had a significantly higher mean concentration of serum FBb (0.638) than other MG subtypes (0.446 for AChR-Ab-positive, 0.537 for seronegative MG patients) and healthy controls (0.434) (p = 0.045). Mean serum iC3b (1.549-1.780) and C4d (0.364-0.395) levels were comparable among the groups.

CONCLUSION

Our results suggest that MuSK-Ab-positive MG patients might have a complement-activating serum factor and the alternative complement pathway might be involved in the pathogenesis of the disease.

Complement levels before and after dives with a high risk of DCS

BACKGROUND

Previously, complement activation has been associated with decompression sickness (DCS). However data, both in humans and in animals, are controversial.

HYPOTHESIS

Complement activation and depletion occurs after exposure to the hyperbaric environment and is associated with increasing risk of DCS.

METHODS

We obtained serological samples from 102 dives (120-300 feet of seawater) with a constant partial pressure of O2 set at 1.3 ATA in thirty-five U.S. Navy diver volunteers. Blood was obtained within one hour of diving and within one hour of surfacing. Plasma was extracted and analyzed for complement depletion. The risk of DCS was estimated using a validated model of DCS risk.

RESULTS

Pre-post dive concentrations of C3a were significantly related to estimated risk of DCS (Figure 1), but the variation in predicted DCS explained by C3a was small (correlation co-efficient (r2 = 0.19, p < 0.0001).

CONCLUSIONS

There was a reduction in total Ca3 levels in divers after exposure to dives with a high estimated risk of DCS. This decomplementation appeared to increase as the estimated risk of DCS increased.

Preservation of antimicrobial properties of complement peptide C3a, from invertebrates to humans

The human anaphylatoxin peptide C3a, generated during complement activation, exerts antimicrobial effects. Phylogenetic analysis, sequence analyses, and structural modeling studies paired with antimicrobial assays of peptides from known C3a sequences showed that, in particular in vertebrate C3a, crucial structural determinants governing antimicrobial activity have been conserved during the evolution of C3a. Thus, regions of the ancient C3a from Carcinoscorpius rotundicauda as well as corresponding parts of human C3a exhibited helical structures upon binding to bacterial lipopolysaccharide permeabilized liposomes and were antimicrobial against gram-negative and gram-positive bacteria. Human C3a and C4a (but not C5a) were antimicrobial, in concert with the separate evolutionary development of the chemotactic C5a. Thus, the results demonstrate that, notwithstanding a significant sequence variation, functional and structural constraints imposed on C3a during evolution have preserved critical properties governing antimicrobial activity.

Identification of plasma protein biomarkers associated with idiopathic pulmonary arterial hypertension

We have employed SELDI-TOF MS to screen for differentially expressed proteins in plasma samples from 27 patients with idiopathic pulmonary arterial hypertension (IPAH) and 26 healthy controls. One ion (m/z approximately 8600) that was found to be elevated in IPAH was validated by SELDI-TOF MS analysis of a second and separate set of plasma samples comprising 30 IPAH patients and 19 controls. The m/z 8600 was purified from plasma by sequential ion exchange and reverse-phase chromatographies and SDS-PAGE. It was identified, following trypsin digestion, by MS peptide analysis as the complement component, complement 4a (C4a) des Arg. Plasma levels of C4a des Arg measured by ELISA confirmed that the levels were significantly higher (p < 0.0001) in IPAH patients (2.12 +/- 0.27 microg/mL) compared with normal controls (0.53 +/- 0.05 microg/mL). A cut-off level of 0.6 microg/mL correctly classified 92% of IPAH patients and 80% of controls. Further studies will be needed to determine its performance as a diagnostic biomarker, whether used alone or in combination with other biomarkers. Nevertheless, this study demonstrates that putative biomarkers characteristic of IPAH can be identified using a conjoint SELDI-TOF MS - proteomics approach.

Complement activation in diabetic ketoacidosis and its treatment

Recent studies support the presence of an inflammatory response during the treatment of diabetic ketoacidosis (DKA). The objectives of this study were to monitor the complement activation products C3a, C4a, Bb, and C5b-9 prior to, during, and after correction of DKA. All patients had increased levels of C3a at 6-8 h and 24 h (P<0.05). C4a was increased in only one patient. Bb showed an upward trend at 6-8 h, and was significantly elevated at 24 h (P<0.05); sC5b-9 was elevated in all patients prior to treatment or in the first 6-8 h of treatment. Results indicate that the alternative pathway may be the primary pathway of activation. These results extend the observation that both DKA and its treatment produce varying degrees of immunologic stress during the time when acute complications are most likely to occur.

Anaphylatoxins in preterm and term labor

OBJECTIVE

The complement system plays a central role in the first line of defense against invading pathogens, and its activation involves the release of potent pro-inflammatory mediators such as anaphylatoxins C3a, C4a and C5a. The aim of this study was to determine whether differences existed in maternal plasma anaphylatoxin concentrations between patients with term and preterm parturition.

STUDY DESIGN

A cross-sectional study was designed to determine the plasma anaphylatoxin concentrations in 296 pregnant women in the following groups: 1) normal pregnancy between 20-36 6/7 weeks (n=64); 2) term not in labor (n=70); 3) term in labor (n=60); and 4) preterm labor with intact membranes (n=102). Women with preterm labor were classified into: a) term delivery (n=24); b) preterm delivery without intra-amniotic infection (IAI) (n=62); and c) preterm delivery with IAI (n=16). Concentrations of C3a, C4a and C5a were determined by ELISAs. Statistical analysis was conducted with non-parametric methods.

RESULTS

1) The median plasma C5a concentration was lower in women at term in labor than in those not in labor (P<0.001). In contrast, there were no differences in plasma C3a and C4a concentrations between the two groups (P>0.05). 2) Among patients with preterm labor, those with IAI had a higher median plasma C5a concentration than those without IAI and those who delivered at term (post-hoc tests P<0.001 and P=0.01, respectively). When comparing the preterm labor subgroups with normal pregnancy, only women with preterm delivery and IAI had a median plasma C5a concentration higher than that of normal pregnant women (Kruskal-Wallis P<0.001, post hoc test P<0.001). There was no difference in the plasma C4a concentration among patients with preterm labor. The median plasma C3a concentration in patients with preterm labor with IAI was higher than in those without IAI (Kruskal-Wallis P=0.01, and post-hoc test P=0.005). There was no difference in the plasma C3a concentrations between women with preterm labor who delivered at term and those with preterm delivery, with or without IAI. In addition, no differences were observed in the median plasma C3a concentration between women with normal pregnancy and those in each of the preterm labor subgroups.

CONCLUSIONS

The maternal plasma concentration of anaphylatoxin C5a is increased in women with preterm labor and IAI, but not in spontaneous labor at term.

The C4A and C4B isotypic forms of human complement fragment C4b have the same intrinsic affinity for complement receptor 1 (CR1/CD35)

Several previous reports concluded that the C4b fragment of human C4A (C4Ab) binds with higher affinity to CR1 than does C4Bb. Because the isotypic residues, (1101)PCPVLD and (1101)LSPVIH in C4A and C4B, respectively, are located within the C4d region, one may have expected a direct binding contribution of C4d to the interaction with CR1. However, using surface plasmon resonance as our analytical tool, with soluble rCR1 immobilized on the biosensor chip, we failed to detect significant binding of C4d of either isotype. By contrast, binding of C4c was readily detectable. C4A and C4B, purified from plasma lacking one of the isotypes, were Cs converted to C4Ab and C4Bb. Spontaneously formed disulfide-linked dimers were separated from monomers and higher oligomers by sequential chromatographic steps. The binding sensorgrams of C4Ab and C4Bb monomers as analytes reached steady state plateaus, and these equilibrium data yielded essentially superimposable saturation curves that were well fit by a one-site binding model. Although a two-site model was required to fit the equilibrium-binding data for the dimeric forms of C4b, once again there was little difference in the K(D) values obtained for each isotype. Independent verification of our surface plasmon resonance studies came from ELISA-based inhibition experiments in which monomers of C4Ab and C4Bb were equipotent in inhibiting the binding of soluble CR1 to plate-bound C4b. Although divergent from previous reports, our results are consistent with recent C4Ad structural data that raised serious doubts about there being a conformational basis for the previously reported isotypic differences in the C4b-CR1 interaction.

Diversity in intrinsic strengths of the human complement system: serum C4 protein concentrations correlate with C4 gene size and polygenic variations, hemolytic activities, and body mass index

Among the genes and proteins of the human immune system, complement component C4 is extraordinary in its frequent germline variation in the size and number of genes. Definitive genotypic and phenotypic analyses were performed on a central European population to determine the C4 polygenic and gene size variations and their relationships with serum C4A and C4B protein concentrations and hemolytic activities. In a study population of 128 healthy subjects, the number of C4 genes present in a diploid genome varied between two to five, and 77.4% of the C4 genes belonged to the long form that contains the endogenous retrovirus HERV-K(C4). Intriguingly, higher C4 serum protein levels and higher C4 hemolytic activities were often detected in subjects with short C4 genes than those with long genes only, suggesting a negative epistatic effect of HERV-K(C4) on the expression of C4 proteins. Also, the body mass index appeared to affect the C4 serum levels, particularly in the individuals with medium or high C4 gene dosages, a phenomenon that was dissimilar in several aspects from the established correlation between body mass index and serum C3. As expected, there were strong, positive correlations between total C4 gene dosage and serum C4 protein concentrations, and between serum C4 protein concentrations and C4 hemolytic activities. There were also good correlations between the number of long genes with serum levels of C4A, and the number of short genes with serum levels of C4B. Thus, the polygenic and gene size variations of C4A and C4B contribute to the quantitative traits of C4 with a wide range of serum protein levels and hemolytic activities, and consequently the power of the innate defense system.

Elevated kallikrein activity in plasma from stable liver transplant recipients

Extensive in vitro conversion of complement components C3 and C4 has been observed in EDTA plasma obtained from a number of stable orthotopic liver transplant recipients (LTR) [Clin. Chem. 45 (1999) 1190]. Consequently, we designed a chromogenic substrate (Ac-Ala-Gly-Leu-Thr-Arg-p-nitroanilide, AGLTR-pNA), based on the C1s cleavage site in complement component C4, in an attempt to identify the plasma proteinase(s) that cleaves C4 in vitro. Average peptidase activity in EDTA plasma obtained from stable LTR (n = 16) was significantly higher (P<0.01) than that in plasma from healthy non-transplant donors (n = 16). This peptidase activity was also detected using commercial substrates designed for specific coagulation proteinases. The plasma proteinase was not inhibited by hirudin, a thrombin inhibitor, but was inhibited by the plasma kallikrein inhibitor D-Phe-Phe-Arg-chloromethylketone, which fails to inhibit C1s. We concluded that the peptidase detected inLTR plasma, using chromogenic substrates including AGLTR-pNA, was plasma kallikrein. Western blot analysis confirmed the presence of kallikrein-alpha-2-macroglobulin complexes (alpha2M) in LTR plasmas. We also demonstrated that kallikrein was not the proteinase responsible for the in vitro cleavage of C4. Elevation of the plasma peptidase activity correlated significantly with recurrent hepatitis C virus (HCV) infection in these liver recipients with a P value <0.02. Significant correlation was not observed between complement activation (i.e. the C4a levels) and recurrent HCV infection (P>0.15); however, C4a levels did correlate with rejection (P<0.02). These results suggest that elevation in plasma peptidase activity and activation of complement do signal different pathological events in LTR, events that appear related to HCV-induced infection and immune tissue injury, respectively.

Deficient APC-cofactor activity of protein S Heerlen in degradation of factor Va Leiden: a possible mechanism of synergism between thrombophilic risk factors

In protein S Heerlen, an S-to-P (single-letter amino acid codes) mutation at position 460 results in the loss of glycosylation of N458. This polymorphism has been found to be slightly more prevalent in thrombophilic populations than in normal controls, particularly in cohorts of patients having free protein S deficiency. This suggests that carriers of the Heerlen allele may have an increased risk of thrombosis. We have now characterized the expression in cell cultures of recombinant protein S Heerlen and investigated the anticoagulant functions of the purified recombinant protein in vitro. Protein S Heerlen was synthesized and secreted equally well as wild-type protein S by transiently transfected COS-1 cells. The recombinant protein S Heerlen interacted with conformation-dependent monoclonal antibodies and bound C4b-binding protein to the same extent as wild-type protein S. Protein S Heerlen displayed reduced anticoagulant activity as cofactor to activated protein C (APC) in plasma-based assays, as well as in a factor VIIIa-degradation system. In contrast, protein S Heerlen functioned equally well as an APC cofactor in the degradation of factor Va as wild-type protein S did. However, when recombinant activated factor V Leiden (FVa:Q506) was used as APC substrate, protein S Heerlen was found to be a poor APC cofactor as compared with wild-type protein S. These in vitro results suggest a possible mechanism of synergy between protein S Heerlen and factor V Leiden that might be involved in the pathogenesis of thrombosis in individuals carrying both genetic traits. (Blood. 2000;96:523-531)

Complement activation in coronary artery bypass grafting patients without cardiopulmonary bypass: the role of tissue injury by surgical incision

STUDY OBJECTIVES

Complement activation is a trigger in inducing inflammation in patients who undergo coronary artery bypass grafting (CABG) and is usually thought to be induced by the use of cardiopulmonary bypass (CPB). In this study, we examined whether tissue injury caused by chest surgical incision per se contributes to complement activation in CABG patients.

DESIGN

Prospective study.

SETTING

Thorax center in university hospital.

PATIENTS

Twenty-two patients undergoing CABG without CPB were prospectively divided into two groups: a small chest incision via an anterolateral thoracotomy representing a minimized tissue injury (lateral group, n = 8), and a conventional median sternotomy representing a large tissue injury (median group, n = 14). Biochemical markers indicating complement activation as well as systemic inflammatory response were determined before, during, and after the operation.

MEASUREMENTS AND RESULTS

Plasma concentrations of complement 3a increased in both the lateral and median groups right after chest incision (p < 0.01 and p < 0.05, respectively) and by the end of operation increased only in the median group (p < 0.01). The terminal complement complex 5b-9 did not increase in the lateral group, but it did increase in the median group both after incision and by the end of the operation (p < 0.05 and p < 0.05, respectively). During surgery, complement 4a did not increase, suggesting that it is the alternative rather than the classic pathway that is involved in complement activation by tissue injury. Postoperatively, interleukin-6 production was greater in the median group (p < 0.01) than the lateral group (p < 0.05), suggesting a more pronounced inflammatory response to a larger chest incision.

CONCLUSIONS

Tissue injury caused by surgical incision contributes to complement activation in CABG patients who are operated on without CPB. A small anterolateral thoracotomy is associated with reduced complement activation in comparison with a median sternotomy.

C4A deficiency due to a 2 bp insertion is increased in patients with systemic lupus erythematosus

OBJECTIVE

The association of C4A deficiency with systemic lupus erythematosus (SLE) is well documented. In Caucasian populations, the most common cause of C4A deficiency is a large gene deletion in linkage disequilibrium with a conserved MHC haplotype. Because of this linkage disequilibrium, it has been difficult to determine which of the genes constitutes the disease susceptibility allele. Evidence from non-caucasoid populations has supported a role for C4A deficiency in SLE. We investigated whether a specific genetic cause of C4A deficiency, not associated with A1, B8, DR3, is found with increased frequency in SLE compared to controls.

METHODS

Polymerase chain reaction was used to identify carriers of a 2 base pair (bp) insertion in exon 29. In total, 188 patients with SLE from the Johns Hopkins lupus cohort and 222 controls were genotyped.

RESULTS

The 2 bp insertion was found more frequently in patients with SLE compared to controls and was more common in Caucasian than in African American SLE patients. There were no clinical differences between patients that carried the mutation and those that did not.

CONCLUSION

The association of this C4A null allele with SLE supports a role for C4A deficiency independent of other MHC associations in the etiopathogenesis of SLE.

Analysis of human C4A and C4B binding to an immune complex in serum

Previous studies using isolated complement proteins have shown that more C4A than C4B binds to certain types of immune complexes. However, the in vivo binding of the C4 isoforms to an immune complex has not been investigated in detail and may differ from events when measured with the isolated proteins. We report here the binding of C4A and C4B to an immune complex of bovine serum albumin (BSA) anti-BSA as it occurs in serum. We found that when using the isolated C4 proteins more C4A than C4B bound to the complex, but in serum similar amounts of C4A and C4B were found to bind. Furthermore, these results were not explainable by a difference in activity between isoforms. In an attempt to explain these results a number of unexpected observations were noted. First C4A, but not C4B, bound specifically to a yet unidentified 38-kD serum protein. Second, when both covalent and non-covalent binding was assessed, we found that as serum concentration increased there followed a concomitant decrease in covalent binding and C4B was more affected than C4A. The potential biological significance of these findings is discussed.

Complement system is not activated in primary biliary cirrhosis

There is controversial evidence suggesting that the classical pathway of complement system is chronically activated in primary biliary cirrhosis (PBC) and that complement activation may be important in development of bile duct injury. We have reevaluated this issue by measuring by-products of complement activation such as C4a, C3a, Bb, and terminal complement complexes (SC5b-9) in plasma of 44 PBC patients with sensitive methods not previously used to detect complement activation in this disease. Age-matched healthy women and patients with chronic hepatitis of different etiology were studied as controls. We found that PBC patients have normal C4a concentrations. This finding argues strongly against chronic classical pathway activation. Although a minor increase of C3a levels was observed in a minority of PBC patients, the C3a/C3 ratio, an index used to evaluate the extent of native protein conversion, was remarkably similar in all groups. Potentially lytic terminal complement complexes were not increased. PBC patients had normal Bb plasma levels, indicating that the alternative pathway is also not activated. C3 concentration was higher in PBC patients than in healthy subjects and in chronic hepatitis patients, particularly in the early stages of the disease. C3 and C4 concentrations became lower in PBC and chronic hepatitis with the progression of the disease. The increase of C3 concentration in PBC does not reflect liver inflammation, since serum levels of C-reactive protein are normal. We found high serum C3 levels in patients with rare chronic cholestatic syndromes without superimposed infections and observed that serum C3 levels paralleled those of bilirubin in a patient with benign recurrent intrahepatic cholestasis. In conclusion, our data indicate that complement is not activated in PBC and that the increase of serum C3 levels is related to cholestasis.

Rapid activation of the complement system by cuprophane depends on complement component C4

Hemodialysis with cuprophane dialyzer membranes promotes rapid activation of the complement system, which is thought to be mediated by the alternative pathway. Complete hereditary deficiency of complement C4, a classical pathway component, in two hemodialysis patients provided the opportunity to investigate a possible role of the classical pathway. In two hemodialysis patients with both C4 isotypes, C4A and C4B, and in one patient with C4B deficiency complement activation occurred immediately after the onset of hemodialysis, with peak levels of C3a and terminal complement complex (TCC) after ten to fifteen minutes. In patients with complete C4 deficiency, C3a and TCC remained unchanged for fifteen minutes and increased thereafter, reaching the highest level after thirty minutes. The leukocyte nadir was also delayed from fifteen to thirty minutes. In vitro incubation of normal, C4A- or C4B-deficient serum with cuprophane caused complement activation after fifteen minutes. In contrast, no activation was observed in sera of four C4-deficient patients. The addition of normal serum or purified human C4 restored the capacity for rapid complement activation. In one patient with severe immunoglobulin deficiency, C3a and TCC levels increased only moderately after 25 minutes of cuprophane dialysis. This patient's serum also exhibited delayed complement activation in vitro, which was normalized after pretreatment of cuprophane with immunoglobulins. Preincubation of normal serum with MgEGTA, a blocker of the classical pathway, inhibited rapid complement activation through cuprophane. As basal levels of C4a are markedly increased in hemodialysis patients (3450 +/- 850 ng/ml) compared to healthy controls (224 +/- 81 ng/ml), no further elevation of C4a was detectable during cuprophane hemodialysis. Incubation of normal serum with cuprophane, however, caused a slight increase in C4a after five minutes. These results indicate that the initial deposition of complement C3b on the cuprophane membrane, necessary for activation of the amplification loop of the alternative pathway, is mediated by the classical pathway C3-convertase C4b2a. We propose an extended concept of complement activation through cuprophane, which is based on four steps: (a) binding of anti-polysaccharide antibodies, (b) classical pathway activation, (c) alternative pathway activation and (d) terminal pathway activation.

Quantitative analysis of C4Ab and C4Bb binding to the C3b/C4b receptor (CR1, CD35)

Complement-dependent clearance of immune complexes in humans is dependent on the activation and binding of the early components of the classical complement cascade. This prevents immune complex precipitation and promotes binding of the complexes by the C4b/C3b complement receptor CR1 (CD35) found on erythrocytes. The fourth component of human complement is encoded by two closely linked genes within the MHC. These genes give rise to the isotypic forms C4A and C4B, and recent studies suggest that CR1 binds activated C4A (C4Ab) to a greater extent than activated C4B (C4Bb). To study this difference in a more quantitative way the binding reactions between CR1 and C4Ab- and C4Bb-coated immune complexes and between CR1 and soluble dimers of C4Ab (C4Ab2) and C4Bb (C4Bb2) were analysed using the native receptor on human erythrocytes. The binding reaction between immune complexes with equivalent amounts of covalently bound C4Ab or C4Bb and erythrocyte CR1 showed a two-fold higher binding of complexes coated with C4A. Furthermore, erythrocyte CR1 bound C4Ab2 with an apparent four-fold higher affinity (Kd approximately 1.4 x 10(-7) M) than C4Bb2 (Kd approximately 4.8 x 10(-7) M), indicating a preferential binding of CR1 for C4A.

Experimental studies on three types of heparin-coated cardiopulmonary bypass circuits

In cardiovascular operations, we have usually used heparin-coated cardiopulmonary bypass circuits with low systemic heparinization. Three types of heparin-coated cardiopulmonary bypass circuits are available in Japan: 2 of the 3 have covalent heparin bonding, and the other has ionic heparin bonding. We studied these circuits in ex vivo experiments to explore which were the best in terms of biocompatibility. In this study we compared the Carmeda system (Medtronic) and the Capiox system (Terumo) with covalent heparin bonding, and the Duraflo-II (Baxter) with ionic heparin bonding, evaluating them in ex vivo experiments. They were primed with fresh human blood, and we studied and compared the platelet counts, fibrinogen, D-dimmer, beta-thioguanine (TG), thrombin-antithrombin complex (TAT), and C3a and C4a of each of them. Additional research will be presented in the future.

Glomerular deposition of the complement C4 isotypes C4A and C4B in glomeruonephritis

BACKGROUND

Complement C4 is a component of the classical complement pathway, which is a major mediator of inflammation in many forms of glomerulonephritis. The two isoforms of C4-C4A and C4B-differ in their physicochemical and functional properties.

METHODS

The glomerular deposition of C4A and C4B was investigated in 39 cases of glomerulonephritis with classical pathway activation using isotype-specific monoclonal antibodies 99H7 (C4A) and 1288 (C4B) and indirect immunofluorescence. Complement C4 phenotypes of all patients were determined by agarose gel electrophoresis and immunoprecipitation.

RESULTS

Three biopsies contained only the isotype C4B. C4 phenotyping revealed complete C4A deficiency in these three patients. Both isotypes C4A and C4B were detected in 36 biopsies. In 19 (53%) thereof staining for both isotypes was identical. In the remaining 17 (47%), staining intensity of C4A predominated over C4B. The distribution of these two staining patterns did not differ between membranous glomerulonephritis and lupus nephritis. They were also independent of C4A and C4B allotypes including the presence or absence of null alleles at either gene locus. In no case was C4B staining stronger than C4A staining. Serum creatinine and proteinuria did not differ between patients with identical and C4A-dominant C4 deposition.

CONCLUSIONS

The most likely but still hypothetical explanation for predominance in glomerular deposition of C4A over C4B in many cases of immune complex-mediated glomerulonephritis is the greater affinity of C4A to protein-containing immune complexes as compared to C4B.

Alkylation of cellulosic membranes results in reduced complement activation

4-Vinyl pyridine was grafted to the surface of the cellulosic membrane Cuprophan, and subsequently alkylated with both C10 and C16 aliphatic chains. Complement activation of heparinized human blood, corrected for anaphylatoxin adhesion, was measured by radioimmunoassay. The surface treatments both yielded substantial reductions in C5a activity, with a lessor reduction in C3a and C4a activity. Alkylation with 10 and 16 carbon chains resulted both in enhancements of albumin adsorption and stability. These enhancements as well as the reductions in complement activation were statistically indistinguishable between the two treatments. The reduction in complement activation was influenced more by adsorption of endogenous albumin and possibly by the vinyl pyridine graft, than the removal of surface active hydroxyl groups from Cuprophan.

Covalently-bound human C4b dimers consisting of C4B isotype show higher hemolytic activity than those of C4A in the C3-bypass complement pathway

The ability to form a covalent dimer of human C4b was investigated with purified isotypes C4A and C4B, and antibody-sensitized liposomes supplemented with C1. In this system, no C4A or C4B formed a complex with the antibody or C1. Whereas both C4A and C4B isotypes formed dimers to a similar extent, C4B formed an ester-linked dimer and C4A an amide-linked dimer. Both of these dimers served as a subunit for the C3-bypass pathway C5 convertase, since liposomes bearing Ab, C1 and a dimer of C4A or C4B, allowed the formation of C5 convertase by the addition of C2. The degree of complement-mediated liposome lysis however, was observed to be 2-3 times higher in the C4B-bearing particles than in those bearing C4A. These results indicate that the second C4b-binding site on the first C4b is different between C4A and C4B, and that in the C3-bypass pathway, C4B has a higher degree of hemolytic activity than C4A, as in the conventional classical complement pathway.

Complement profiles in human skin lymph during the course of irritant contact dermatitis

Using microsurgery a superficial peripheral lymph vessel draining the skin of the upper and medial part of the foot was cannulated on the lower leg of two healthy human volunteers. An irritant contact dermatitis was induced 2 days later by the application of 10% sodium lauryl sulphate to the drained skin area. After a further 3 days the spontaneously regressing skin reaction was treated with clobetasol propionate. Lymph was continuously collected in two aliquots per day for 7 days. The levels of total protein, of albumin and globulins, and of complement components of the classical, the alternative and the lytic pathway as well as the C4A and C4B gene products and the regulatory proteins FB, C1INH, C4BP, FH and FI were determined by ELISA and radial immunodiffusion techniques. Postoperatively, the levels of complement proteins and globulins in the lymph were 5-10 times lower than those in normal human serum, but increased during the course of the skin reaction, while the irritant contact dermatitis did not induce a change in their plasma concentration. In comparison to the baseline, the mean values for C1q, C1r, C2, C5, C6, C7, C8, C9, FB, C1INH, C4BP, FH and FI exhibited a 3-5-fold increase, C3, total C4, albumin and the alpha 1-globulin fraction a 6-9-fold increase, and C1s, C4A, C4B, FB and alpha 2-, beta- and gamma-globulins a 10-20-fold increase.(ABSTRACT TRUNCATED AT 250 WORDS)

Granulocyte superoxide anion and elastase release during cardiopulmonary bypass

Cardiopulmonary bypass (CPB) is known to induce several pathogenic responses in cardiovascular surgery. To explore leukocyte activation during PCB, we investigated superoxide anion (O2-) production by granulocytes in 6 patients undergoing aortocoronary bypass surgery. O2- production was determined with chemiluminescence amplified by a cypridina luciferin analogue. Granulocytes collected from the blood in the arterial site of the CPB circuit were stimulated by phorbol myristate acetate, n-formyl-methionyl-leucyl-phenylalanine, and opsonized zymosan. All the stimulators failed to disclose a significant difference between the magnitude of chemiluminescence during and after CPB. However, significant complement activation was detected, and the plasma level of granulocyte elastase increased gradually during and after CPB. This discrepancy between the unchanged O2- production by stimulated granulocytes and the increase in inflammatory mediators including granulocyte elastase may be due to sequestration of activated granulocytes in extravascular tissues. Namely, it was highly likely that activated granulocytes responsible for the increased plasma elastase level were sequestered and remained outside the blood circulation.

Covalent binding properties of the human complement protein C4 and hydrolysis rate of the internal thioester upon activation

The complement proteins C3 and C4 have an internal thioester. Upon activation on the surface of a target cell, the thioester becomes exposed and reactive to surface-bound amino and hydroxyl groups, thus allowing covalent deposition of C3 and C4 on these targets. The two human C4 isotypes, C4A and C4B, which differ by only four amino acids, have different binding specificities. C4A binds more efficiently than C4B to amino groups, and C4B is more effective than C4A in binding to hydroxyl groups. By site-directed mutagenesis, the four residues in a cDNA clone of C4B were modified. The variants were expressed and their binding properties studied. Variants with a histidine residue at position 1106 showed C4B-like binding properties, and those with aspartic acid, alanine, or asparagine at the same position were C4A-like. These results suggest that the histidine is important in catalyzing the reaction of the thioester with water and other hydroxyl group-containing compounds. When substituted with other amino acids, this reaction is not catalyzed and the thioester becomes apparently more reactive with amino groups. This interpretation also predicts that the stability of the thioester in C4A and C4B, upon activation, will be different. We measured the time course of activation and binding of glycine to C4A and C4B. The lag in the binding curve behind the activation curve for C4A is significantly greater than that for C4B. The hydrolysis rates (k0) of the thioester in the activated proteins were estimated to be 0.068 s-1 (t1/2 of 10.3 s) for C4A and 1.08 s-1 (t1/2 of 0.64 s) for C4B. These results indicate that the difference in hydrolysis rate of the thioester accounts, at least in part, for the difference in the binding properties of C4A and C4B.

Effect of thiol compounds on human complement component C4

Thiol compounds have been investigated as inhibitors of the covalent binding reaction of human complement protein C4 using Sepharose-C1s as a combined activating and binding surface. o- and p-substituted aminothiophenols are equally effective inhibitors, whereas the m-substituted compound is a less potent inhibitor. The anti-hypertensive drug captopril is also shown to inhibit the covalent binding reaction. A comparison of the effects of these compounds on the covalent binding reaction of isolated C4A and C4B has been made. Results suggest that a Pro-to-Leu substitution in C4B is likely to account for the differences in inhibitory potency of C4B compared with C4A observed with the aromatic inhibitors.

The interaction of soluble human complement receptor type 1 (sCR1, BRL55730) with human complement component C4

Human CR1 is a membrane-bound protein which plays an important role in the control of the human complement system. In addition to its involvement in the processing and clearance of immune complexes with C3b or C4b on their surface, CR1 acts as a cofactor for the proteolysis of C3b and C4b by Factor I. sCR1 is a recombinant, soluble form of CR1 which retains the cofactor activities of CR1, and is of potential therapeutic value for the suppression of complement-mediated tissue damage in vivo. An assay has been established using microtitre plates to explore the binding of sCR1 to the two isotypes of C4, C4A and C4B, and to C4 fragments. Specific binding of 125I-sCR1 to C4b and ammonia-treated C4 has been demonstrated. The binding of 125I-sCR1 to ammonia-treated C4 is dependent on pH and ionic strength, decreasing with an increase in pH and with an increase in ionic strength. At physiological ionic strength, up to twice as much 125I-sCR1 bound to ammonia-treated C4A as bound to ammonia-treated C4B. This preference of sCR1 for binding to the C4A isotype has implications for the clinical association of immune complex disease with C4A null alleles.

Identification of a surface structure in the fourth component of human complement, C4, which becomes hidden upon activation by C1(-)s

Treatment of complement component C4 with C1(-)s and methylamine induces a series of conformation changes such as to generate functional binding sites. A monoclonal antibody (mAb), Al 121/6, which does not inhibit the haemolytic activity of C4 was found to bind to native C4 and C4d, but not to C4b and methylamine-treated C4, unless these C4 derivatives were denatured. These results suggested that a linear epitope for mAb Al 121/6 in the C4d domain is originally located at the surface of C4 and becomes hidden as a result of conformational changes induced by C1(-)s or methylamine treatment. The hidden linear epitope was exposed again upon further cleavage of C4b into C4c and C4d. Trypsin digestion of C4d and its chemical modification with phthalic anhydride suggested that the epitope is located at the C-terminal 13 kDa region of C4d and that lysine residues are involved in the epitope. There is a single lysine residue at 1259 in the 13 kDa C-terminal side of C4d and the synthetic undecapeptide Leu1254-Asp1264 was found to inhibit the binding of C4 to mAb Al 121/6, suggesting that the epitope for mAb Al 121/6 is involved in the sequence. The N-terminal portion of the peptide is partly overlapping, with a highly hydrophobic amino acid sequence spanning residues Ala1249-Leu-Leu-His-Leu-Leu-Leu1255. The surface hydrophobicity of C4 has been reported to decrease upon treatment with C1(-)s and methylamine. So it appears that the hydrophobic sequence spanning Ala1249-Leu1255 may be hidden, together with the linear epitope, into the inner region of C4 upon treatment with C1s and methylamine.

Plasma histamine but not anaphylatoxin levels correlate with generalized urticaria from infusions of anti-lymphocyte monoclonal antibodies

Anti-lymphocyte monoclonal antibodies have shown promise in trials for therapy of lymphocyte malignancies but are associated with a high frequency of immediate-type anaphylactoid reactions. We have previously demonstrated that these immediate-type anaphylactoid reactions are not mediated by immunoglobulin E to anti-lymphocyte monoclonal antibodies. To gain insight into the mechanisms of these immediate-type anaphylactoid reactions, we measured plasma levels of histamine and anaphylatoxins (C3a, C4a, C5a) during 11 infusions in eight patients who received anti-lymphocyte monoclonal antibodies (T101 and Lym-1). Three patients experienced generalized urticaria (two with severe angioedema); a fourth patient had three isolated hives but without generalized manifestations of an immediate-type anaphylactoid reaction. Plasma histamine levels after infusions that were associated with generalized urticaria were significantly higher than those during infusions that were not associated with generalized urticaria (mean, 3.47 vs 0.18 ng/ml, p less than 0.001). Increases in C3a and C4a levels were observed after some infusions, but these did not correlate with generalized urticaria. Measurable rises in plasma C5a levels after infusions were not detected. Although these data should be viewed as preliminary considering the limited number of patients studied, the observed histamine release demonstrates that mast cell or basophil activation that is not mediated by immunoglobulin E to anti-lymphocyte monoclonal antibodies occurs in the pathogenesis of immediate-type anaphylactoid reactions from anti-lymphocyte monoclonal antibodies. Although activation of the classical complement pathway may occur in some anti-lymphocyte monoclonal antibody infusions, this does not appear to explain immediate-type anaphylactoid reactions.(ABSTRACT TRUNCATED AT 250 WORDS)

Complement activation during storage of blood under normal blood bank conditions. Effects of proteinase inhibitors and leukocyte depletion

During storage of CPD-A1 preserved whole blood factors of the complement cascade become activated, as evidenced by a rapid increase in the concentrations of C3a-desArg and C4a-desArg. After 10 to 14 days of whole blood storage, the elevations of C3a and C4a levels were highly significant. This increase was paralleled by an increase in the concentration of the lysosomal proteinase elastase from polymorphonuclear (PMN) granulocytes. By contrast, the concentration of the C3 activator complex C4b2b remained unchanged even after 3 weeks of storage. The supplementation of the anticoagulant CPD-A1 with the polyvalent-proteinase-inhibitor aprotinin and the specific elastase-inhibitor eglin C failed to inhibit complement activation, whereas leukocyte depletion could partially abolish the increase of the concentration of C4a, but had no effect on C3a concentrations. These observations support the notion that cleavage of C4 during storage of whole blood is partially leukocyte dependent, whereas the activation of C3 is possibly caused by the activation of the alternate pathway of the complement system by contact of plasma with plastic surfaces.

Plasma levels and mode of excretion of the anaphylatoxins C3a and C4a in renal disease

Plasma levels of the anaphylatoxins C3a and C4a were examined in patients suffering with various renal diseases. Raised levels were observed in a considerable number of patients; although such elevation could be ascribed to in vivo complement activation in cases of immune complex glomerulonephritis, we found that raised plasma C4a levels appeared to be related to impaired renal function, suggesting that C4a anaphylatoxin is cleared by the kidneys. No such relationship was found in the case of the anaphylatoxin C3a suggesting the possible existence of another mechanism of elimination of C3a.

Effect of anticoagulant on biocompatibility in membrane plasmapheresis

The effect of heparin or citrate anticoagulation on blood cellular, complement pathway and coagulation pathway was investigated in a membrane plasma exchange procedure. Two membrane plasma separators constructed of cellulose di-acetate (CA) and polyvinyl chloride (PVC) were evaluated with heparin or citrate alone for anticoagulation in a 26 year old male with myasthenia gravis. Maximum white blood cell counts decrease was 21% at 30 min for the CA with heparin while no decrease was observed for the other schemes. Platelet counts changes were comparable between heparin and citrate, while the PVC groups showed less changes than the CA groups. The CA groups, regardless of the type of anticoagulant used, indicated that complement activation occurred via the classical pathway within the module in addition to the activation via alternative pathway for the CA with heparin. In the PVC groups, complement activation was noted to occur only when heparin was used for anticoagulation. PT and PTT showed slight increases with citrate, while they were remarkably prolonged with heparin. Citrate showed less changes in cellular and humoral factors compared to heparin. CA with heparin was the most activating combination of membrane material and anticoagulant, while the PVC with citrate was the least activating combination.

Differences between C4A and C4B in the handling of immune complexes: the enhancement of CR1 binding is more important than the inhibition of immunoprecipitation

There are two isotypes of C4--C4A and C4B--, encoded within the major histocompatibility complex with quite different properties. In this study we have compared purified C4A and C4B with regard to their ability to prevent immune complex precipitation and to enhance the binding of both preformed and nascent immune complexes to the receptor CR1 on red cells. C4A was modestly more effective than C4B at inhibiting immunoprecipitation, particularly in antibody excess. In the CR1 binding assay C4A was markedly more effective than C4B in enhancing binding to CR1. This difference was seen with both preformed and nascent immune complexes at equivalence and antibody excess. Thus the major differences between C4A and C4B in regard to immune complex handling is at the level of CR1 binding. Given the strong association of C4A* QO alleles with immune complex-mediated diseases like systemic lupus erythematosus, these findings have important pathogenetic implications.

The influence of the geometry of the dialyzer and the composition of the dialysate in activating the complement system

During hemodialysis there is a complex interaction between the patient and the extracorporeal circuit that activates the complement system, among others. To better understand the influence of the dialyzer geometry and the dialysate composition, we compared hollow fiber versus parallel plate dialyzers and acetate versus bicarbonate dialysates and their role in the production of C3a, C4a and C5a. There was no significant difference in the plasmatic levels of these anaphylotoxins and their des-Arg derivates, as measured by RIA, in either dialyzer. The same was true when the dialysate in question had a different composition. We thus concluded that neither the geometric configuration of the dialyzer nor the composition of the dialysate influence their biocompatibility as regards the activation of the complement system, and that the differences that have been described shall have to be explained in another manner or assessed by methods other than those used in this study.

Differences in the metabolism of C4 isotypes in patients with complement activation

The metabolism of the C4 allotypes C4A3,B1 and C4A3,BO was studied in five healthy control subjects and six patients with active immunological disease (five with systemic lupus erythematosus and one with rheumatoid arthritis). The specific aim was to identify any differences in the metabolism of C4A and C4B gene products that may be linked to their documented functional differences in vitro. The fractional catabolic rate of C4A3,B1 in patients was significantly greater than that of C4A3,BO (3.98 +/- 1.37 versus 3.31 +/- 0.85%/h; mean +/- s.d.; P less than 0.05) but there was no difference in control subjects (1.95 versus 1.99%/h). The extravascular:intravascular (EV:IV) distribution ratio of C4A3,B1 was also greater in both patients (1.19 +/- 0.36 versus 0.97 +/- 0.35; P less than 0.01) and controls (0.43 +/- 0.11 versus 0.31 +/- 0.13; P = 0.01). We conclude that C4B1 was catabolized more rapidly than C4A3 in patients with pathological complement activation but not in control subjects. This difference could reflect the relatively greater extravascular distribution (i.e. EV:IV ratio) of C4B at sites of immune complex deposition or, alternatively, different rates of catabolism of inactive C4 isotypes (iC4b).

Demonstration of neutrophil chemotactic anaphylatoxins in human dandruff

In contrast to scales collected from the scalps of nine healthy individuals where a few parakeratotic cells are observable, a large number of parakeratotic cells associated with some infiltrated polymorphonuclear leukocytes (PMNLs) were found in the scales obtained from 11 individuals complaining of dandruff. Therefore, we determined the neutrophil chemotactic properties of the water-soluble extracts of dandruff scales and normal control scalp scales. Aqeous extracts fractionated by Sephadex G-75 showed a potent chemotactic activity only in the fractions of the dandruff patients that eluted with cytochrome C marker (cyt C; molecular weight, 12 kDa). It was comparatively stable to heat but was greatly inhibited by the addition of anti-C5 antiserum. Radioimmunoassay demonstrated that, although small amounts of C5a and C4a anaphylatoxins were demonstratable even in the extracts of normal scalp, they were found in significantly increased amounts in the extracts of dandruff. Moreover, there was a significantly positive correlation between C5a and C4a concentrations in these extracts. These results suggest that classical complement pathway activation with resultant production of C5a anaphylatoxin is involved in the migration of PMNLs into the lesional skin of dandruff.