Quantitative studies of the secretion of complement component C3 by resident, elicited and activated macrophages. Comparison with C2, C4 and lysosomal enzyme release

Underweight Is an Independent Risk Factor for Renal Function Deterioration in Patients with IgA Nephropathy

Studies on the relationship between body mass index (BMI) and renal progression in IgA Nephropathy (IgAN) were limited, especially for underweight patients with IgAN. To elucidate the clinical features and effect of underweight on renal function deterioration in this disease, we recruited IgAN patients with diagnostic age ≥18 years old and a baseline estimated glomerular filtration rate (eGFR) ≥15 ml/min/1.73m² from our center between 1985 and 2014. Patients secondary to systemic diseases or follow-up less than 6 months were excluded. All patients’ clinical data at renal biopsy and during follow-up were recorded. Renal outcome was defined as end-stage kidney disease (ESRD). Baseline body mass index (BMI) was calculated by weight (kg) over squared height (m²). According to WHO Asian guideline, BMI was categorized as follows: <18.5kg/m² (underweight), 18.5–22.99kg/m² (normal weight), 23–27.49kg/m² (overweight) and obese (≥27.5 kg/m²). Of 930 primary IgAN patients enrolled in this study, mean age at renal biopsy was 37.6 years and 49.2% were men. Totally, 114 (12.3%) ESRD occurred after a mean follow-up of 47.1 months. More ESRD happened in underweight patients (17.3%) compared to patients with normal weight (13.2%), overweight (11.0%) or obesity (9.5%). By multivariate Cox regression analysis, underweight was independently associated with a higher risk of ESRD after adjustment for demographic characteristics and clinical variables (HR: 3.5, 95% CI: 1.3–9.5, P = 0.01) comparing to normal weight. Underweight patients had lower hemoglobin, serum uric acid, triglycerides, cholesterol and lymphocyte counts than patients with normal weight. Furthermore, BMI was positively correlated with serum C3 (r = 0.25, p <0.001). Our research finds that underweight is an independent risk factor for kidney disease progression in IgAN, which might be associated with malnutrition status and decreased C3 levels.

Anti-Ganglioside Antibodies Induce Nodal and Axonal Injury via Fcγ Receptor-Mediated Inflammation

Guillain-Barré syndrome (GBS) is a postinfectious autoimmune neuropathy and anti-ganglioside antibodies (Abs) are strongly associated with this disorder. Several studies have implied that specific anti-ganglioside Abs induce neuropathy in patients with axonal forms of GBS. To study the mechanisms of anti-ganglioside Abs-induced neuropathy, we established a new passive transfer mouse model by L5 spinal nerve transection (L5SNT; modified Chung's model) and systemic administration of anti-ganglioside Abs. L5SNT causes degeneration of a small proportion of fibers that constitute sciatic nerve and its branches, but importantly breaks the blood-nerve barrier, which allows access to circulating Abs and inflammatory cells. Our studies indicate that, in this mouse model, anti-ganglioside Abs induce sequential nodal and axonal injury of intact myelinated nerve fibers, recapitulating pathologic features of human disease. Notably, our results showed that immune complex formation and the activating Fc gamma receptors (FcγRs) were involved in the anti-ganglioside Abs-mediated nodal and axonal injury in this model. These studies provide new evidence that the activating FcγRs-mediated inflammation plays a critical role in anti-ganglioside Abs-induced neuropathy (injury to intact nerve fibers) in GBS.

Expression of complement components and regulators by different subtypes of bone marrow-derived macrophages

Under inflammatory conditions, macrophages can differentiate into different functional subtypes. We show that bone marrow-derived macrophages constitutively express different levels of various complement-related genes. The relative expression levels are C1qb > Crry > CFH > C3 > C1r > CFB > DAF1 > CD59a > C2 > C1INH > C1s > C4. Upon activation, the expression of C1r, C1s, C3, C2, CFB, and C1INH was up-regulated, and CFH, CD59a, and DAF1, down-regulated in M1 (induced by interferon-γ + lipopolysaccharides (LPS)) and M2b (induced by immune complex + LPS) macrophages. The expression of C4 and CFH was slightly up-regulated in interleukin (IL)-10-induced M2c macrophages. Complement gene expression in IL-4-induced M2a macrophages was weakly down-regulated as compared to resting M0 macrophages. Higher levels of C3, C1INH, and CFB but lower levels of CFH expression in M1 and M2b macrophage suggests that they may be involved in the alternative pathway of complement activation during inflammation.

Triacylglycerols and body fat mass are possible independent predictors of C3 in apparently healthy young Brazilian adults

OBJECTIVE

To evaluate the association between serum concentrations of complement factor-3 (C3) with anthropometric, biochemical, and lifestyle features in healthy young adults.

METHODS

From 157 young healthy adults 18 to 35 y old, anthropometric measurements and body composition, systolic and diastolic blood pressures, and lifestyle data were collected and analyzed. Blood samples were collected after a 12-h fast for the determination of glucose, triacylglycerols, total cholesterol, high-density lipoprotein cholesterol, low-density lipoprotein cholesterol, insulin, C3, ceruloplasmin, and uric acid.

RESULTS

Complement factor-3 correlated directly with body mass index (r = 0.23417, P = 0.0032), body fat mass (bioelectrical impedance analysis; r = 0.33407, P < 0.0001), percentage of body fat (bioelectrical impedance analysis; r = 0.26873, P = 0.0007), waist circumference (r = 0.21266, P = 0.0075), insulin (r = 0.26152, P = 0.0009), homeostasis model assessment of insulin resistance (r = 0.24831, P = 0.0017), total cholesterol (r = 0.23335, P = 0.0033), triacylglycerols (r = 0.38435, P < 0.0001), and other outcome measurements. In the multiple linear regression analysis, triacylglycerols (r(2) = 0.1379, P < 0.0001) and body fat mass (bioelectrical impedance analysis; r(2) = 0.0621, P = 0.0010) were independently associated with the C3 concentration after adjusting for age, gender, smoking status, and physical activity.

CONCLUSION

Complement factor-3 seems to be related to several anthropometric and biochemical measurements in healthy young adults. These results demonstrate an independent role of triacylglycerols, a component of the metabolic syndrome, and body fat mass as possible predictors of C3 concentrations. Thus, C3 can be used as an early marker for metabolic syndrome manifestations.

Combined proteomic and metabolomic profiling of serum reveals association of the complement system with obesity and identifies novel markers of body fat mass changes

Obesity is associated with multiple adverse health effects and a high risk of developing metabolic and cardiovascular diseases. Therefore, there is a great need to identify circulating parameters that link changes in body fat mass with obesity. This study combines proteomic and metabolomic approaches to identify circulating molecules that discriminate healthy lean from healthy obese individuals in an exploratory study design. To correct for variations in physical activity, study participants performed a one hour exercise bout to exhaustion. Subsequently, circulating factors differing between lean and obese individuals, independent of physical activity, were identified. The DIGE approach yielded 126 differentially abundant spots representing 39 unique proteins. Differential abundance of proteins was confirmed by ELISA for antithrombin-III, clusterin, complement C3 and complement C3b, pigment epithelium-derived factor (PEDF), retinol binding protein 4 (RBP4), serum amyloid P (SAP), and vitamin-D binding protein (VDBP). Targeted serum metabolomics of 163 metabolites identified 12 metabolites significantly related to obesity. Among those, glycine (GLY), glutamine (GLN), and glycero-phosphatidylcholine 42:0 (PCaa 42:0) serum concentrations were higher, whereas PCaa 32:0, PCaa 32:1, and PCaa 40:5 were decreased in obese compared to lean individuals. The integrated bioinformatic evaluation of proteome and metabolome data yielded an improved group separation score of 2.65 in contrast to 2.02 and 2.16 for the single-type use of proteomic or metabolomics data, respectively. The identified circulating parameters were further investigated in an extended set of 30 volunteers and in the context of two intervention studies. Those included 14 obese patients who had undergone sleeve gastrectomy and 12 patients on a hypocaloric diet. For determining the long-term adaptation process the samples were taken six months after the treatment. In multivariate regression analyses, SAP, CLU, RBP4, PEDF, GLN, and C18:2 showed the strongest correlation to changes in body fat mass. The combined serum proteomic and metabolomic profiling reveals a link between the complement system and obesity and identifies both novel (C3b, CLU, VDBP, and all metabolites) and confirms previously discovered markers (PEDF, RBP4, C3, ATIII, and SAP) of body fat mass changes.

Serum C3 is a stronger inflammatory marker of insulin resistance than C-reactive protein, leukocyte count, and erythrocyte sedimentation rate: comparison study in an elderly population

OBJECTIVE

This study was performed to ascertain the relative relevance of some inflammatory markers in insulin resistance.

RESEARCH DESIGN AND METHODS

Four inflammatory markers (leukocyte count, erythrocyte sedimentation rate [ESR], high-sensitivity C-reactive protein [CRP], and C3 complement) were assessed as possible determinants of the homeostasis model assessment (HOMA) index, together with the five elements of the metabolic syndrome (National Cholesterol Education Program Expert Panel on Detection, Evaluation, and Treatment of High Blood Cholesterol in Adults [Adult Treatment Panel III] definition), total cholesterol, physical activity, and four indicators of adiposity (BMI, waist circumference, percent body fat, and hepatic steatosis) in an unselected population of 990 subjects aged 65-91 years (the Pianoro Study).

RESULTS

In univariable analysis, C3, CRP, and leukocyte count, but not ESR, were significantly correlated with HOMA index. In multivariable analysis, C3 remained associated with insulin resistance with the highest partial R(2) value (0.049), independently of all other covariates. The other most significant (P < 0.0001) determinants of HOMA index were total cholesterol (inverse association, R(2) = 0.026), waist circumference (R(2) = 0.023), triglycerides (R(2) = 0.022), and hepatic steatosis (R(2) = 0.021) (R(2) = 0.450 for the whole model). The adjusted relative risks of having the metabolic syndrome for the subjects with inflammatory markers in the high tertile, with respect to those with lower values, were (prevalence ratio [95% CI]): 1.77 (1.41-2.22) for C3, 1.38 (1.12-1.70) for leukocyte count, 1.17 (0.94-1.46) for CRP, and 1.13 (0.91-1.40) for ESR.

CONCLUSIONS

Of the four inflammatory markers simultaneously assessed in our elderly population, only C3 was strongly associated with insulin resistance, independently of the components of the metabolic syndrome and the main indexes of abdominal and general obesity.

Hostility, anger, and depression predict increases in C3 over a 10-year period

We examined the relation of hostility, anger, and depression to 10-year changes in the third (C3), and fourth (C4) complement in 313, apparently healthy male participants enrolled in the Air Force Health Study (AFHS), a 20-year study designed to evaluate the health consequences of dioxin exposure. Hostility, depression, and anger were assessed using subscales from the Minnesota Multiphasic Personality Inventory (MMPI), which was administered in 1985. Given the high intercorrelations among these psychological scales, we used a principal component analysis to generate a composite score representing the linear combination of the hostility, anger, and depression scales. The dependent variables, C3 and C4 levels, were determined from samples collected in 1992, 1997, and 2002. Regression analyses controlling for age, race, alcohol use, body mass index, and cigarette use as well as onset of disease, and use of lipid lowering and blood pressure medications during follow-up revealed a significant timexcomposite score interaction for C3 complement (p<.0003), but not C4. Post-hoc analyses revealed that high composite scores were associated with larger 10-year increases in C3. These observations suggest that men who are hostile and are prone to experience frequent and intense feelings of anger, and depression show activation of the complement system, and specifically increases in C3, that may contribute to the development of coronary heart disease.

Effects of weight loss and risk factor treatment in subjects with elevated serum C3, an inflammatory predictor of myocardial infarction

BACKGROUND

Serum C3 is an inflammatory predictor of myocardial infarction and a covariate of fasting insulin and several endogenous risk factors. This study was performed to ascertain whether risk factor control may reduce elevated C3 concentrations.

METHODS

After traditional risk factor and C3 assessment in 1100 unselected men aged 55-64 years, 238 men with persistently elevated C3 levels (>=1.19 g/l, high tertile) were randomised into 2 groups: 43 controls, who were referred to their general practitioner, and 195 subjects who were intensively treated with diet, and anti-hypertensive or antidiabetic drugs according to specific indications, without anti-dyslipidemic drugs.

RESULTS

After three months in the treated subjects significant decrements of body weight, blood pressure, blood glucose and serum lipids were obtained, with stable C3 levels (while in controls a 3.3% increase occurred, P=0.02). The factors associated with a C3 decrement >5% were a high baseline C3 level, a recent acute inflammation, physical activity, belonging to the treated group, and a significant reduction in body weight, triglycerides or blood glucose. However, in multivariate analysis only an elevated baseline C3 (P<0.0001), a weight loss >2% (P=0.0009) and physical activity (P=0.02) remained independently associated with a C3 decrement >5% (R(2)=0.14).

CONCLUSIONS

Only weight loss and physical activity, but not traditional risk factor lowering, could independently induce a significant C3 decrease. Thus, C3 elevation is associated with, but probably not caused by, traditional risk factors.

Cross-sectional study of complement C3 as a coronary risk factor among men and women

In the present study, we examined (i) whether C3 (complement C3) was an independent marker of prevalent CHD (coronary heart disease), and (ii) which preferential associations existed between C3 and some cardiovascular risk factors when jointly analysed with CRP (C-reactive protein) and fibrinogen. In a cohort of 756 unselected adults, 39% of whom had the metabolic syndrome, C3 and other risk variables were evaluated in a cross-sectional manner. In a logistic regression model for the likelihood of CHD, a significant OR (odds ratio) of 3.5 [95% CI (confidence intervals), 1.27 and 9.62)] for C3 was obtained after adjustment for smoking status, TC (total cholesterol) and usage of statins. A similar model, also comprising systolic blood pressure, with a cut-off point of >or=1.6 g/l C3 exhibited a 1.9-fold risk (95% CI, 1.01 and 3.58) compared with individuals below the cut-off point. Both analyses displayed an adjusted OR of 1.37 for each S.D. increment in C3. The significant relationship of C3 with a likelihood of CHD also proved to be independent of CRP. In multiple linear regression models, associations were tested for each acute-phase protein with measures of obesity, fasting insulin, triacylglycerols (triglycerides), TC, HDL (high-density lipoprotein)-cholesterol, physical activity, smoking status, diagnosis of metabolic syndrome and family income. When both genders were combined, C3 was independently associated with serum triacylglycerols, waist circumference, BMI (body mass index) and TC. CRP was independently associated with waist circumference, TC, family income (inversely) and physical activity, and fibrinogen with BMI, TC, smoking status and metabolic syndrome. In summary, elevated levels of complement C3 are associated with an increased likelihood of CHD independent of standard risk factors and regardless of the presence of acute coronary events, suggesting that C3 might be actively involved in coronary atherothrombosis. Unlike CRP and fibrinogen, C3 was preferentially associated with waist girth and serum triacylglycerols.

Critical review of acylation-stimulating protein physiology in humans and rodents

In the last few years, there has been increasing interest in the physiological role of acylation-stimulating protein (ASP). Recent studies in rats and mice, in particular in C3 (-/-) mice that are ASP deficient, have advanced our understanding of the role of ASP. Of note, the background strain of the mice influences the phenotype of delayed postprandial triglyceride clearance in ASP-deficient mice. Administration of ASP in all types of lean and obese mice studied to date, however, enhances postprandial triglyceride clearance. On the other hand, regardless of the background strain, ASP-deficient mice demonstrate reduced body weight, reduced leptin and reduced adipose tissue mass, suggesting that ASP deficiency results in protection against development of obesity. In humans, a number of studies have examined the relationship between ASP, obesity, diabetes and dyslipidemia as well as the influence of diet, exercise and pharmacological therapy. While many of these studies have small subject numbers, interesting observations may help us to better understand the parameters that may influence ASP production and ASP action. The aim of the present review is to provide a comprehensive overview of the recent literature on ASP, with particular emphasis on those studies carried out in rodents and humans.

Different associations of C-reactive protein, fibrinogen and C3 with traditional risk factors in middle-aged men

BACKGROUND

Some acute phase proteins are associated with both ischemic events and traditional risk factors. Since they are strongly interrelated, each of them partly reflects the characteristics of other proteins. This study was carried out to ascertain the specific preferential associations of some acute phase proteins with traditional risk factors for atherosclerotic disease.

METHODS

High-sensitivity C-reactive protein, fibrinogen and C3-complement were assessed in 288 unselected men aged 55-64 years. Three multiple linear regression analyses were performed, in which each of the three acute phase proteins was considered the dependent variable of both traditional risk factors and the other two proteins.

RESULTS

The three acute phase proteins strongly correlated with each other. Moreover, C-reactive protein was independently associated with triglycerides (P<0.0001), age (P=0.0130), body mass index (P=0.0179), and acute (P=0.0280) and chronic (P=0.0582) inflammations (R2=0.17). Fibrinogen was associated with alcohol consumption (inversely, P=0.0001) and smoking (P=0.0598) (R2=0.06). Finally, C3 was associated with insulin (P<0.0001), cholesterol (P=0.0001), sedentarity (P=0.0028), glucose (P=0.0077), and systolic blood pressure (P=0.0124) (R2=0.28).

CONCLUSIONS

When simultaneously studied in multivariate analysis, acute phase proteins have different preferential associations with traditional risk factors, a probable consequence of their involvement in different cellular activations and metabolic processes.

Complement biosynthesis by mononuclear phagocytes

Mononuclear phagocytes are an important in vivo source of a wide range of complement components. They are able to rapidly up-regulate or down-regulate complement synthesis in response to many different pharmacological and biological stimuli. This ability is likely to make a significant contribution to maintaining host defences particularly in peripheral tissues. The important role of molecular biology in the study of complement biosynthesis by mononuclear phagocytes will be emphasised.

Secretion, cleavage and binding of complement component C3 by the human monocytic cell line U937

Secretion of complement component C3 by U937 cells was studied. Preliminary evidence for a cell-associated proteolytic activity specific for C3 is given, as well as for a covalent-like binding of C3 fragments to the cell membranes. Secretion of C3, in the presence of 10 ng of phorbol 12-myristate 13-acetate/ml, is 120-140 ng/10(6) cells per 24 h on the third day after addition of the activator. As shown by SDS/polyacrylamide-gel electrophoresis, the intracellular pro-C3 (200 kDa) and the extracellular secreted C3 (alpha-chain 110 kDa and beta-chain 75 kDa) are identical with the forms of C3 previously characterized from human serum. Incubation of U937 cells in the presence of exogenous radiolabelled C3 shows that membrane-bound proteinase(s), not related to the classical-pathway or the alternative-pathway C3 convertases, is (are) able to cleave C3; this cleavage leads to the binding of the resulting C3 fragments to the cell membrane through reaction of membrane acceptors with the carbonyl group of C3 revealed after disruption of the intramolecular thioester bond. The proteolysis appears to be fairly specific to C3, as C4, which also possesses an intramolecular thioester bond, is not cleaved and does not bind to the cells. p-Nitrophenyl p'-guanidinobenzoate (1 mM) and di-isopropyl phosphorofluoridate (2 mM) are potent inhibitors of the proteolysis, whereas soya-bean trypsin inhibitor (1 mM), leupeptin (0.1 mg/ml) and 1,10-phenanthroline (1 mM) were ineffective. Immunological characterization of the cell-bound C3 fragments with monoclonal antibodies shows an evolution of the proteolysis of the fragments from iC3b to C3dg epitopes. Extraction of membrane-bound fragments by detergent, followed by SDS/polyacrylamide-gel electrophoresis, shows two fragments, of 43 kDa and 46 kDa, with C3dg-like characteristics.

The production of C3, PGE2 and TxB2 by splenic, alveolar, and peritoneal guinea pig macrophages

The synthesis and release of C3, PGE2, and TxB2 by cultured splenic, alveolar and peritoneal guinea pig macrophages in 24 hour culture was determined. There were significant differences in C3 production among all three sources of macrophages. Splenic macrophages produced significantly less PGE2 than alveolar or peritoneal macrophages. Peritoneal macrophages produced significantly more TxB2 than splenic or alveolar macrophages. The cells from the different sources appear to be different populations of macrophages.

Characteristics of the beta-glucan receptor of murine macrophages

Phagocytosis of heat-killed yeast (HK-yeast), zymosan, and glucan particles by thioglycollate-elicited mouse peritoneal macrophages (Tg-macrophages) was inhibited by soluble glucan polymers/oligomers. The inhibitory capacity of soluble glucans decreased steeply with the decrease in the degree of polymerization (DPn); i.e., the concentration at which 50% inhibition of phagocytosis was attained was 0.23 microgram/ml for glucan 1 (DPn 24.8), 0.8 microgram/ml for glucan 2 (DPn 21.9), and greater than 40 micrograms/ml for glucan 3 (DPn 13.8). The glucan polymers were obtained by partial hydrolysis of glucan particles with formic acid (90%, 95 degrees C, 20 min) and fractionation according to solubility in ethanol water mixtures. A short preincubation (5 min, 4 or 37 degrees C) of Tg-macrophages with glucan 1 led to a subsequent inhibition of HK-yeast phagocytosis. Recovery of the phagocytic function was slow (27% in 3 h; 68% in 5 h) and required protein synthesis. beta-Glucan receptor expression was also suppressed by dexamethasone treatment. Mannan exerted at high concentrations (5 mg/ml) a partial inhibitory activity which was totally abrogated by beta-glucanase treatment. Treatment of macrophages with glucan together with mannan did not enhance the inhibitory capacity of glucan beyond the component abrogated by enzyme treatment. Contribution of local opsonization of HK-yeast to the phagocytic response (involvement of complement receptors) was indirectly negated; (a) glucan 1 which inhibits HK-yeast phagocytosis by up to 95% is not an activator of complement and therefore could not compete for the opsonizing proteins; (b) cycloheximide treatment in itself inhibited only partially HK-yeast phagocytosis whereas it inhibited the reexpression of the glucan receptors; (c) glucan 1 did not affect the phagocytosis of serum opsonized HK-yeast. Thus under the experimental conditions described, phagocytosis of HK-yeast by murine macrophages is mediated by and large by the beta-glucan receptors, while the mannose receptors and complement receptors do not contribute to the process.

Biosynthesis of the third component of complement in rat liver epithelial cell lines and its stimulation by effector molecules from cultured human mononuclear cells

Rat liver epithelial cell lines, growing in a serum-supplemented medium, synthesize and secrete into the culture medium the third component of complement (C3). We studied the regulation of C3 production in this system. We found that human peripheral blood mononuclear leukocytes in culture released one or more soluble factors which stimulated rat liver epithelial cells to produce increased quantities of C3. This stimulating effect was strongly enhanced when the mononuclear cell cultures were treated with phytohemagglutinin, a T-lymphocyte mitogen. The factor(s) failed to enhance C3 biosynthesis by rat dermal fibroblasts, which are known to produce this protein. This reveals a tissue-specific differential response between the fibroblasts and the liver epithelial cells. The physical and chemical characteristics, such as heat sensitivity, 2.8 M ammonium sulphate precipitation, and lower activity after digestion by proteases unambiguously indicate that the effector molecules are proteins. When the crude supernatant of mononuclear leukocytes was fractionated by gel filtration, the stimulating factor(s) eluted as two peaks with apparent molecular weight of 25 to 60 and 15 to 20 kdalton, respectively. As to the cellular origin of the C3-stimulating factor(s), several observations were made: (a) in separate cultures containing either T-cells or monocyte-enriched populations from the same sample of blood mononuclear cells, no activity was detected in the presence or absence of phytohemagglutinin, (b) conditioned media from each of these cultures could not substitute for the corresponding intact cell populations, and (c) the addition of purified T-cells to the monocyte-enriched population in the presence of phytohemagglutinin restored the production of the stimulating activity by the mixed culture. Finally, experiments were carried out to verify whether monokine interleukin 1 affects the hepatic C3 biosynthesis. It was demonstrated that interleukin 1 enhanced this biosynthesis, but could not completely substitute for conditioned medium from stimulated mononuclear cells.

Determination of the complement component C2 by ELISA in human serum and bronchoalveolar lavage fluids

In order to measure the concentration of the human complement component C2 in various biological fluids, an enzyme linked immunosorbent assay (ELISA) was developed. This assay was highly sensitive and allowed to detect as few as 400 pg of C2 in a sample volume of 150 microliters (i.e. 2.6 ng/ml). This is a 10- to 15-fold increase in sensitivity with regard to the conventional hemolytic test. As assessed by an immunoblot analysis, our anti-C2 antiserum was able to detect native C2 as well as the cleavage fragments C2a and C2b generated upon complement activation through the classical pathway. Thus, complement activation involving the classical pathway can easily be evidenced by comparing functional (hemolytic) and immunochemical (ELISA) C2 assays which respectively do not and do reveal activated C2. When C2 was assayed in either normal human serum or bronchoalveolar fluids, in both ELISA and hemolytic tests, a highly significant correlation was observed between the two assays (P less than or equal to 0.01). The specific C2 activity (i.e. functional hemolytic activity/ng C2 assayed in ELISA) was higher in serum than in bronchoalveolar lavage fluids from both normal volunteers and patients with pulmonary diseases.

Stimulation of complement component C3 synthesis in macrophagelike cell lines by group B streptococci

Complement levels and complement activation are key determinants in streptococcus-induced inflammatory responses. Activation of macrophage functions, such as complement synthesis, by group B streptococci (GBS) was examined as a possible component of GBS-induced chronic inflammation. Using an enzyme-linked immunosorbent assay, secreted C3 from mouse macrophagelike cell lines (PU5-1.8 and J774A.1) was monitored after cultivation with GBS. Whole, heat-killed GBS (1 to 10 CFU per macrophage) of both type Ia and III strains induced 25 to 300% increases in secreted C3 in both cell lines after a 24-h cultivation. GBS-treated cell lines exhibited increases in secreted lysozyme (10%) and in cellular protein (25 to 50%). Inhibition of macrophage phagocytosis by cytochalasin B inhibited GBS stimulation of C3. Purified cell walls of GBS type III strain 603-79 (1 to 10 micrograms/ml) also enhanced C3 synthesis. Local enhancement of macrophage C3 production by ingested streptococci or by persistent cell wall antigens may serve to promote chronic inflammatory responses.

Third component of rat complement. Purification from plasma and radioimmunoassay in culture media from cell lines

A double antibody radioimmunoassay for rat C3 has been developed. The assay required the preparation of C3 from plasma. A new purification procedure using ion exchange high performance liquid chromatography is described. The final product was homogeneous on SDS-PAGE analysis. Rat C3 has an apparent molecular weight of 187,000 and is composed of two polypeptide chains with molecular weights of 125,000 and 73,000, respectively. The purified C3 antigen with high hemolytic reactivity, as assessed by its specific functional activity, was used in preparing anti-C3 sera to perform a specific radioimmunoassay for quantifying C3 in the presence of heterologous sera contained in the cell culture media. All the validating criteria, such as precision, recovery and dilution studies, were investigated. The high sensitivity of the method allowed replicate determination of C3 in small aliquots of the cell culture medium.

Biosynthesis of the third component of complement (C3) by the human monocytic-cell line U-937. Induction by phorbol myristate acetate

Phorbol myristate acetate (PMA)-stimulated human monocyte-like cells (U-937) were found to synthesize the third component of complement (C3), as shown by enzyme-linked immunosorbent assay and immunoprecipitation from [35S]methionine-labelled culture supernatants. C3 synthesis occurred at a rate of about 160 ng of C3/24 h per 10(6) cells on day 7 after addition of PMA; it was blocked by cycloheximide treatment and was restored after removal of the inhibitor. SDS/polyacrylamide-gel-electrophoretic analysis of the immunoprecipitated protein showed that the size and subunit structure of the newly synthesized C3 were identical with those of plasma C3, and that a single-chain intracellular precursor was present in the cell lysates. Haemolytic assays showed that the synthesized C3 fully expressed functional activity in early culture within 4 h. After longer culture, a loss of haemolytic activity was observed. The possibility that newly secreted C3 is cleaved by U-937 cells themselves was suggested.

Complement potentiates the degradation of myelin proteins by plasmin: implications for a mechanism of inflammatory demyelination

A previous finding, that the basic protein in lyophilized bovine myelin was degraded by macrophage-conditioned media in the presence of plasminogen, suggested that the macrophage-secreted plasminogen activator, along with plasminogen, might have a role in destruction of myelin during inflammatory demyelination. To approximate more closely the conditions expected in vivo, plasmin, or macrophage supernatants plus plasminogen, were incubated with freshly homogenized bovine white matter or freshly isolated myelin, as distinguished from lyophilized myelin. Under these conditions basic protein was not degraded. Phospholipase or lysolecithin potentiated the degradation of basic protein in fresh bovine myelin by plasmin; however, the cultured macrophages did not secrete significant amounts of phospholipase and plasminogen activator simultaneously into the culture media after activation with any of several different agents. Recently myelin was shown to activate complement. After preincubation of fresh myelin with guinea pig serum, as a source of complement, the basic and proteolipid proteins were vulnerable to plasmin or to macrophage-conditioned media plus plasminogen. C3-depleted and C4-deficient sera were not effective, suggesting that these complement components were required for the serum effect. Hypothetically, then, degradation of myelin proteins in the CNS could be initiated by plasminogen activator, secreted by infiltrating macrophages, plus complement and plasminogen, which could enter the CNS through lesions in the blood-brain barrier.

A possible self-regulating mechanism mediated by C3b-acceptor-bound C3b generated by stimulated macrophages

Macrophages have been shown to produce C3 and to bear Fc receptors (FcR), and besides the various C3 receptors, they possess C3b acceptors (C3bA) as well as surface proteases capable of cleaving C3. Using the immune adherence method, we demonstrated that the amount of covalently fixed (i.e., C3bA-bound) C3b is markedly increased upon cell stimulation by phorbol myristate acetate or aggregated IgG, even in the absence of C3. The enhancement of nascent C3b (C3bx) binding to C3bA on these cells could be reversed by inhibiting the process at different stages, using either cycloheximide, phenyl-methyl-sulphonyl-fluoride, salycil hydroxamic acid, or methylamine. On the basis of our present results and earlier results, we propose a self-regulatory mechanism by which activated, C3-producing macrophages cleave C3 by their surface proteases. C3bx generated in this way fixes covalently to C3bA of the producer cells, resulting in the inhibition of FcR on these cells.

Pretranslational regulation of the synthesis of the third component of complement in human mononuclear phagocytes by the lipid A portion of lipopolysaccharide

The third component of complement (C3) is a plasma glycoprotein with a variety of biologic functions in the initiation and maintenance of host response to infectious agents. While the hepatocyte is the primary source of plasma C3, mononuclear phagocytes contribute to the regulation of tissue availability of C3. Lipopolysaccharide (LPS), a constituent of cell walls of gram-negative bacteria, consists of a polysaccharide moiety (core polysaccharide and O antigen) covalently linked to a lipid portion (lipid A). Using metabolic labeling with [35S]methionine, immunoprecipitation, and SDS-polyacrylamide gel electrophoresis, we examined the effects of LPS on synthesis of C3 by human mononuclear phagocytes as well as synthesis of the second component of complement (C2), factor B, lysozyme, and total protein. LPS increased C3 synthesis 5-30-fold without affecting the kinetics of secretion of C3 or the synthesis of C2, lysozyme, or total protein. Factor B synthesis was consistently increased by LPS. Experiments with lipid A-inactivated LPS (alkaline treated), LPS from a polysaccharide mutant strain, and lipid X (a lipid A precursor) indicated that the lipid A portion is the structural element required for this effect. Northern blot analysis demonstrated at least a fivefold increase in C3 mRNA in LPS-treated monolayers, which suggests that the regulation of the increase in C3 synthesis is pretranslational. C2 mRNA and factor B mRNA were increased approximately twofold. The availability of specific gene products in human mononuclear phagocytes that respond to LPS should permit understanding of the molecular regulation of more complex functions of these cells elicited by LPS in which multiple gene products are coordinately expressed.

An in vitro system to study listericidal capacity of macrophages from separate mice: resident macrophages exhibit different activation patterns

An in vitro system with macrophages from individual mice was established to study their listericidal capacity. Because no antibiotics were used, bacterial killing was really due to macrophages in short-term culture. To restrict the extracellular growth of bacteria, cell culture medium was changed at 1-h intervals. We demonstrated that intracellular growth of listeria in macrophage pools from untreated animals varies considerably. Obviously, preactivated macrophages are constantly present, so that the common procedure of using macrophage pools from several animals is no longer acceptable. In addition, we demonstrated that in vitro mixtures of listeria-immune macrophages of one animal with cells from untreated animals at different ratios exhibit enhanced bacterial killing above a mere additive effect. Consequently, by using macrophages from individual untreated mice, we found that cells of different animals exhibited various activation stages, although unstimulated, inbred specific-pathogen-free mice of the same age, weight, and sex were used. When equal numbers of macrophages from untreated separate animals were mixed in vitro, intracellular growth of listeria was only moderate; that is, the number of preactivated macrophages of the individual animals determined listerial growth in the pooled preparation. Furthermore, we showed that identical doses of phorbol myristate acetate exerted different effects on the listericidal activities of macrophages as a function of their preactivation states. These experiments clearly demonstrate the advantage of using macrophages from individual mice for in vitro studies of macrophage activation.

Chemically modified low density lipoproteins as inducers of enzyme release from macrophages

Macrophages carry receptors on their surface for acetylated low density lipoprotein (ac-LDL). Receptor-mediated endocytosis of ac-LDL is followed by intracellular cholesterol accumulation. We investigated whether occupation of these binding sites evokes the release of hydrolytic enzymes from mouse peritoneal macrophages cultured for up to 48 h. ac-LDL at concentrations ranging from 25-250 micrograms protein/ml was noted to promote in a dose-dependent fashion secretion of the neutral proteinase elastase (EC 3.4.21.37) and the lysosomal acid hydrolases N-acetyl-beta-glucosaminidase (EC 3.2.1.30), beta-glucuronidase (EC 3.2.1.31), beta-galactosidase (EC 3.2.1.23), alpha-mannosidase (EC 3.2.1.24) and cathepsin D (EC 3.4.23.5). This stimulatory effect was non-cytotoxic. LDL modified by treatment with malondialdehyde was also capable of augmenting enzyme liberation into culture supernates. These findings may have implications for some aspects of the atherosclerotic process.

Cytotoxic factor(s) released from stimulated mouse peritoneal macrophages

Mechanisms of macrophage-mediated cytotoxicity against a tumor-cell line (L-929 cells) were analyzed. Culture supernatants were harvested from mouse peritoneal macrophages cultivated for 3 days in the absence or presence of the stimulating agents Escherichia coli endotoxin or zymosan. The supernatants from stimulated cultures were cytotoxic for the tumor cells, evaluated by measuring release of radio-activity during subsequent 4 days' culture of 14C-thymidine-labelled tumor cells in the supernatants. Cytotoxicity was verified by counting cells per culture. Corresponding results were obtained from co cultures of stimulated macrophages and tumor cells, in accordance with a previous study. Selective release of af lysosomal enzyme (beta-glucuronidase) was shown in the supernatants from endotoxin- or zymosan-stimulated cultures, while reduced levels of glucose were seen in all supernatants from macrophage cultures. Dialysis of supernatants against fresh medium reduced the toxic activity somewhat. Dialysis restored the glucose content to optimal levels, while the enzyme activity was unchanged. Heating of supernatants to 56 degrees C for 30 min reduced the cytotoxicity along with a reduction in enzyme activity; 70 degrees C for 30 min removed both cytotoxic activity completely. Heating had no effect on the glucose content of the supernatants. The present data indicate that macrophage-mediated tumor cytotoxicity may be performed through release of heat-labile soluble factor(s) which co-variate with the secretion of a lysosomal enzyme from stimulated macrophages.

Anaphylatoxin C3a enhances mucous glycoprotein release from human airways in vitro

Because C3a may be generated during the course of pulmonary inflammatory reactions, we investigated the ability of C3a to affect mucous glycoprotein (MGP) secretion from cultured human airways. C3a, but not C3a des Arg, caused a dose-related increase in MGP release (maximal after 4-6 h), with as little as 15 micrograms of C3a per milliliter stimulating a 40% increase. The experimental evidence suggested that immunologically specific C3a was required for the secretagogue actions, as monospecific anti-C3a inhibited the reaction, as well as specifically absorbing the secretagogue from solution. Moreover, it appeared that C3a does not require mast cell activation, eicosanoid generation, or macrophage-derived mucus secretagogue synthesis for its effect, since (a) no evidence of histamine release accompanied C3a-induced MGP release, and dibutyryl cAMP failed to affect C3a-induced MGP release, while reducing the actions of reversed anaphylaxis; (b) MGP release caused by C3a was not influenced by eicosatetraynoic acid or specific cyclooxygenase inhibitors, and no leukotrienes were detectable on the supernatants of C3a-stimulated airways; and (c) cycloheximide failed to affect C3a secretion-stimulating actions. Thus, C3a is a potent mucus secretagogue, and, possibly, acts directly as a glandular stimulant. It seems likely that C3a generated in the course of pulmonary inflammation might contribute to the mucus secretion associated with pulmonary infections.

Monoclonal antibody detection of IncF group plasmid-encoded TraT protein in clinical isolates of Escherichia coli

The TraT protein specified by IncF group plasmids mediates surface exclusion and bacterial resistance to the lethal activities of serum. In this study, an anti-TraT protein monoclonal antibody was generated which failed to react with TraT+ bacteria but which efficiently detected solubilized TraT protein in Western blots and in an enzyme-linked immunosorbent assay. Use of this antibody to screen clinical and nonclinical isolates of Escherichia coli for the production of TraT protein revealed its presence in a modest proportion (38%) of normal fecal strains, a significantly higher proportion of clinical strains (51 to 73%), and an even higher proportion (78 to 88%) of clinical strains concomitantly producing the K1 capsule, an important virulence factor of E. coli.

Production of C3 as a marker of lymphokine-mediated macrophage activation

C3 production was assayed using an enzyme-linked immunosorbent assay (ELISA) in cell-free supernatants harvested from thioglycollate-elicited macrophages exposed to a variety of macrophage stimulating and activating agents. Macrophage monolayers treated with the stimulating agents starch, glycogen, and zymosan secreted three- to four-fold less C3 (mean 12 ng/10(5) cells/12 hr) than macrophages exposed to lymphokines containing macrophage-activating factor (MAF) (mean C3 production 44 ng/10(5) cells/12 hr). The increased production of C3 in macrophages exposed to MAF parallels the ability of these macrophages to acquire tumoricidal capacity as monitored in an in vitro 72 hr tumor cell cytotoxicity assay using B16 melanoma cells. Macrophages previously rendered tumoricidal by exposure to MAF and which are refractory to further challenge by MAF following decay of their tumoricidal properties, do not produce C3 on rechallenge with MAF. Exposure of refractory macrophages to liposome-encapsulated MAF overcomes the refractory state and induces re-expression of the tumoricidal phenotype and C3 production. We conclude that quantitative detection of macrophage-generated C3 antigen provides a useful biochemical marker for monitoring the acquisition of tumoricidal properties in macrophages exposed to MAF and offers a sensitive assay for screening novel agents that activate macrophages via mechanisms similar to MAF.

Formation of EAC142 and EAC1423 with macrophage culture supernatant containing the secreted complement components C1 to C3

Culture supernatants of thioglycollate-elicited guinea pig peritoneal macrophages contained hemolytic C1, C4, C2 and C3, whereas hemolytic C5, C6, C7, C8 or C9 were not detected. Activity of C1, C2 and C3 increased up to a 48 h culture period, whereas C4 activity already declined in 2 day old cultures. After secretion, the hemolytic activity of C1 was least stable in culture supernatant. Sensitized sheep erythrocytes (EA) when incubated with culture supernatant initiated activation and functional cooperation of secreted C1 to C3 as indicated by formation of EAC142 and EA1423 intermediates. Decay and regeneration with purified C2 was shown for EAC142 and deposition of C3 fragments on EAC1423 was demonstrated with anti-C3. On an average, supernatants of 2 day old macrophage cultures were most suitable for formation of EAC142 and EAC1423 . The rate of EAC142 and EAC1423 formation, and also of C2 and C3 inactivation, during incubation of EA with culture supernatant was slow; addition of purified C1 to culture supernatant, however, greatly enhanced the same reactions of EA with supernatant which indicated that C1 was the rate limiting factor. Local secretion of hemolytic C1, C4, C2 and C3 by macrophages may have an important role in antimicrobial defense mechanisms due to the well-known functional cooperation between macrophages and activated C3.

Synthesis of complement by macrophages and modulation of their functions through complement activation

During the last decade considerable progress has been made to characterize intimate functional links between macrophages, a major cellular component of immunoinflammatory responses, and the complement system representing the major humoral mediator of inflammation. Macrophages of various species and tissue sites have been shown to synthesize and release most of the complement components providing these cells with their own "pericellular" complement system. Circumstantial evidence for the assembly of both classical and alternative pathway convertases has been adduced. An intricate network of feedback loops involving endogenous and extrinsic factors operates to adjust complement production to acute requirements, for example augmenting production in the face of accelerated turnover at sites of inflammation, and returning it to baseline levels once the inflammatory stimulus has subsided, in order to maintain a fine-tuned balance. The molecular mechanisms underlying regulation of complement synthesis by macrophages are beginning to be elucidated by use of gene technology. On the other hand, complement activation products exert a number of effects on macrophages via specific surface receptors causing internalization of offending agents, microbes, and immune complexes, promotion of intracellular killing, controlling migration behavior, inducing release of potent biologic substances such as lysosomal enzymes, arachidonic acid metabolites, and interleukin 1. In these interactions, two important humoral mediator systems of inflammation, the complement system and the arachidonic acid cascade, are functionally linked at the level of the macrophage. Stimulation of the release of immunomodulating compounds from macrophages invoke a role for complement in immune regulation. This multifaceted interplay is of particular importance considering the mobility of macrophages that allows them to gain almost unrestricted access to sites of ongoing immunoinflammatory responses. The time seems to have come to abandon the petrified thinking in socalled systems as, for instance, humoral versus cellular, specific versus unspecific, and to proceed to interlocking functions guided by physiology proper.

Use of monoclonal and polyclonal antibodies as structural and topographical probes for hepatic epoxide hydrolase

Monoclonal antibodies have been prepared against rat liver epoxide hydrolase (EH), some of which gave precipitation lines on immunodiffusion against pure EH suggesting the presence of repetitive structural domains on the enzyme. Using ELISA, with polyclonal antibodies to rat and rabbit liver EH, reactivity and therefore structural similarities between EH of all species tested, including human, were observed. This was in contrast to immunodiffusion results demonstrating the limitations of the latter technique. Using monoclonal antibodies in ELISA, greatest structural similarity was between rat, mouse, and Syrian hamster EH and relatively little between rat and human. Two of the antibodies reacted with nearly all species tested and may be directed towards critical sites on the enzyme. This and most of the EH molecule would appear to be localised on the cytoplasmic surface of the endoplasmic reticulum.

Activation of macrophages by substance P: induction of oxidative burst and thromboxane release

Substance P (SP), a putative neuropeptide transmitter, was examined for its effects on macrophages. Guinea-pig peritoneal macrophages were purified by adherence, challenged with SP and incubated for up to 18 h. Culture supernatants were collected to determine the release of O-2, H2O2 and TXB2. SP dose-dependently evoked O-2 and H2O2 production by C. parvum-activated macrophages and liberation of TXB2 from albumin-elicited macrophages. Generation of these proinflammatory macrophage products by SP may be relevant in the context of neuroinflammatory disease.

Tuftsin stimulates the release of oxygen radicals and thromboxane from macrophages

The physiologically occurring tetrapeptide, tuftsin (Thr-Lys-Pro-Arg), was examined for its effects on guinea pig peritoneal macrophages. Adherent macrophages (møo) were exposed to tuftsin at concentrations ranging from 10(8) to 10(6) M, and the release of oxygen radicals and the arachidonic acid cyclo-oxygenation product, thromboxane B2 (TXB2), was studied. Tuftsin causes both albumin-elicited and C. parvum-activated møo to set free superoxide anion (O2) and hydrogen peroxide (H2O2). It also stimulates the liberation of TXB2 from albumin-elicited møo. The demonstrated induction of the release of toxic oxygen species from møo by tuftsin may explain how tuftsin-augmented møo-mediated cytotoxicity is accomplished.