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PubMed1981

Stimulation of human neutrophil chemiluminescence by soluble immune complexes and antibodies to neutrophils.

Activation of the neutrophil surface membrane may occur with a variety of stimuli, leading to enhanced glucose oxidation via the hexose monophosphate shunt and production of toxic oxygen radicals such as superoxide anion. This metabolic stimulation may be accompanied by light emission or chemiluminescence. The objective of these studies was to determine the effects of soluble and insoluble immune complexes, IgG aggregates, and rabbit anti-neutrophil serum on neutrophil activation as measured by chemiluminescence. Also, the uptake of immune complexes by neutrophils was determined and was correlated with the solubility of the complexes and the levels of induced chemiluminescence. The results indicate that stimulation of neutrophil chemiluminescence and uptake of immune complexes by neutrophils were both closely correlated with the percent precipitation of the immune complexes. Insoluble immune complexes that were avidly ingested by neutrophils also stimulated maximum levels of chemiluminescence. Nevertheless, elevated levels of chemiluminescence were induced by soluble immune complexes that were poorly ingested by neutrophils. Similarly, soluble aggregated IgG induced elevated levels of neutrophil chemiluminescence in a dose-dependent manner. Aggregated IgG induced up to sixfold higher levels of neutrophil chemiluminescence than did equal amounts of monomeric IgG. Finally, rabbit anti-neutrophil serum also caused increased levels of neutrophil chemiluminescence. Since previous studies have shown that sera from some patients with rheumatoid arthritis and Felty's syndrome have increased amounts of neutrophil-binding IgG due to the presence of both immune complexes and neutrophil-reactive antibodies, the effect of these sera on neutrophil chemiluminescence was studied. Positive correlations were observed between the level of neutrophil chemiluminescence induced by the sera and the amount of serum IgG neutrophil-binding activity (r = 0.72, p less than 0.001) as well as the level of immune complexes determined by C1q binding (r = 0.76, p less than or equal to 0.001). Such neutrophil activation by immune complexes or antibodies may reflect production of toxic oxygen radicals and could subsequently affect neutrophil function.

Antibodies↗
PubMed1981

Circulating immune complexes and autoantibodies in lung cancer.

The sera of 80 newly diagnosed lung-cancer patients have been examined for immune complexes and autoantibodies. Control subjects consisted of 20 bronchitic patients and 150 normal blood donors. Immune-complex measurements used 4 established and sensitive techniques (Raji cell assay, fluid and solid-phase C1q assays and conglutinin-binding assay) and a 5th newly devised technique based on the binding of polyethylene-glycol-precipitated immune-complex-rich serum fractions to Staphylococcus aureus. Using the Raji cell assay and the S. aureus binding assay to measure immune complexes, both newly diagnosed lung cancer patients and bronchitic patients had significantly higher prevalences of immune complexes than normal controls, but the two groups of patients did not differ significantly in either prevalence or quantity of immune complexes. When techniques which depend solely upon complement fixation (C1q assays and conglutinin binding) were used, only meagre quantities of immune complexes were found, and in at most 15% of newly diagnosed lung-cancer patients. The presence of autoantibodies in newly diagnosed cancer patients and controls appeared to correlate with the increase in the detectable prevalence of immune complexes.

Adolescent↗
PubMed2001

Levels of antibodies against C1q and 60 kDa family of heat shock proteins in the sera of patients with various autoimmune diseases.

Previously a strong positive correlation was found between antibodies to C1q (C1qAb) and antibodies against human heat shock protein (hsp60) and mycobacterial hsp65 in HIV infected patients. Here the levels of these antibodies were measured in the sera of patients with different autoimmune diseases (122 systemic lupus erythematosus (SLE), 55 systemic sclerosis, 33 undifferentiated connective tissue disease (UCTD), 27 primary Raynaud syndrome, 21 rheumatoid arthritis (RA), 14 polymyositis/dermatomyositis (PM/DM), and 192 healthy blood donors. The prevalence of IgG C1qAb was found to be high (P<0.0001 as compared to the healthy controls) only in the SLE group. The levels of the anti-hsp60 (P=0.0094) and anti-hsp65 (P=0.0108) antibodies were high only in the UCTD patients. No correlation was found between the C1qAb and anti-hsp antibodies in any group except a significant (P=0.011) positive correlation between C1qAb and hsp65 antibodies in the patients with UCTD. These findings indicate that the autoantibodies against C1q are heterogeneous: in different diseases different types of C1qAb may dominate.

Adult↗
PubMed2003

Structural flexibility of multifunctional HABP1 may be important for regulating its binding to different ligands.

Hyaluronan-binding protein 1 (HABP1)/p32/gC1qR was characterized as a highly acidic and oligomeric protein, which binds to different ligands like hyaluronan, C1q, and mannosylated albumin. It exists as trimer in high ionic and reducing conditions as shown by crystal structure. In the present study, we have examined the structural changes of HABP1 under a wide range of ionic environments. HABP1 exhibits structural plasticity, which is influenced by the ionic environment under in vitro conditions near physiological pH. At low ionic strength HABP1 exists in a highly expanded and loosely held trimeric structure, similar to that of the molten globule-like state, whereas the presence of salt stabilizes the trimeric structure in a more compact fashion. It is likely that the combination of the high net charge asymmetrically distributed along the faces of the molecule and the relatively low intrinsic hydrophobicity of HABP1 result in its expanded structure at neutral pH. Thus, the addition of counter ions in the molecular environment minimizes the intramolecular electrostatic repulsion in HABP1 leading to its stable and compact conformations, which reflect in its differential binding toward different ligands. Whereas the binding of HABP1 toward HA is enhanced on increasing the ionic strength, no significant effect was observed with the two other ligands, C1q and mannosylated albumin. Thus, although HA interacts only with compact HABP1, C1q and mannosylated albumin can bind to loosely held oligomeric HABP1 as well. In other words, structural changes in HABP1 mediated by changes in the ionic environment are responsible for recognizing different ligands.

Anilino Naphthalenesulfonates↗
PubMed1986

Function of the follicular dendritic cell in the germinal center of lymphoid follicles.

The authors made an immunocytochemical examination of the germinal centers (GCs) of (1) lymph follicles in physiological lymph nodes and (2) extra-nodal tissues of divergent diseases including thyroid disorders, rheumatoid arthritis, Warthin's tumor and Kimura's disease (Eosinophilic lymphfolliculoid granuloma). In these germinal centers, the presence of immunoglobulins (IgG and IgM), early acting complement components (C1q, C4, C3c, C3d), receptors for C3b and C3d and dendritic reticulum cell-1 was demonstrated in lace-like network patterns which were proven electron-microscopically to coincide with the surface of follicular dendritic cells. IgE was distributed in a lace-like pattern in the GCs of proliferating follicles of Kimura's disease, in which the lysis of follicles was frequently observed. This lysis appeared to be related to the presence of complement components. In the germinal centers of extra-nodal tissues, including the thyroid tissues accompanying the lymph follicles, rheumatoid arthritis synovial tissues as well as Warthin's tumors, thyroglobulin, rheumatoid factor and salivary amylase were detected as specific antigens, occurring in lace-like patterns. It is possible that follicular dendritic cells may play a role in the genesis of GCs and be responsible for the immune response through C3 receptors.

Adenolymphoma↗
PubMed1984

Monoclonal anti-mouse macrophage antibodies recognize the globular portions of C1q, a subcomponent of the first component of complement.

One of seven monoclonal antibodies generated against mouse macrophages (M phi) was found to recognize isolated heterologous C1q. This antibody was shown to be cytotoxic and to react in a strain-independent way with mouse M phi derived from bone marrow cells as well as with M phi from the peritoneal cavity; it did not react, however, with mouse granulocytes, thymocytes, or T and B lymphocytes. The hemolytic activity of fluid phase C1q was inhibited to 50% at a 2 X 10(-4) dilution of hybridoma supernatant, whereas a 100-fold higher concentration was required to inhibit C1q bound to immune complexes ( EAC1q ) to the same extent. It was demonstrated that this antibody recognizes the isolated globular, Fc-binding portions of the C1q molecule and reacts with the A and B chains. Because M phi have been shown to synthesize C1q, the Fc-recognizing subcomponent of the first component of complement, evidence was provided that endogeneous C1q can serve as an Fc receptor on M phi during secretion. This fact was demonstrated by a dose-dependent inhibition of Fc-receptor activity for EIgG by the F(ab')2 fragment of this monoclonal antibody. These experiments further support the concept that C1q produced by M phi functions on the surface as an Fc-recognizing molecule before it is released and incorporated into the macromolecular complex of serum C1.

Animals↗
PubMed1994

Regulation of C1q receptor expression on human polymorphonuclear leukocytes.

The C1q receptor (C1qR) is expressed on a variety of cells, including polymorphonuclear leukocytes (PMN), in which stimulation by the C1qR leads to activation as measured by superoxide production. To investigate the expression and modulation of the C1qR on PMN, the binding of biotinylated C1q to PMN in suspension was measured by flow cytometry. Biotinylated C1q bound in a saturable and specific manner to PMN and the use of low ionic strength buffers enhanced binding. Covalent coupling of C1q to Sepharose beads allowed the affinity precipitation of a single 125-kDa band from surface iodinated PMN. The apparent molecular mass of the C1qR increased to 135 kDa upon reduction. Freshly isolated PMN had a uniform expression of C1qRs and phorbol myristate acetate induced a unimodal up-regulation of receptors. The inflammatory peptide FMLP rapidly up-regulated receptors by up to fivefold, and the high level of expression remained constant over 45 min. Taxol inhibited the FMLP induction of C1qR up-regulation, indicating that the ability to move the intracellular stores of C1qR depends on normal microtubule functioning. Thus, the C1qR is a constitutively expressed protein of the human PMN plasma membrane and it is rapidly up-regulated from a discrete intracellular pool of preformed molecules with the same kinetics as CR1 and CR3. It is likely that the C1qR is a component of the PMN complement receptor exocytic vesicle (CREV), in which CR1 and CR3 are also stored.

Carrier Proteins↗
PubMed1986

Characterization of C1q receptor expression on human phagocytic cells: effects of PDBu and fMLP.

The receptor-mediated binding of C1q to human phagocytic cells was investigated in this study. By using a C1q binding assay, we determined that purified, elutriated monocytes expressed an average of 4.6 X 10(5) C1q receptors (C1qR) per cell, with an equilibrium binding constant (Keq) of 0.91 X 10(7) (M-1). When analyzed in an identical manner, the polymorphonuclear leukocytes (PMN) expressed an average of 4.2 X 10(5) C1qR per cell, with a Keq for C1q of 1 X 10(7) (M-1). Fluorescent flow cytometric analysis showed that C1q was bound by 98% of the monocytes studied. Further, the pattern formed by these cells was consistent with a normal log distribution, indicating that this was a homogeneous population of cells. When PMN were assayed with flow cytometry, however, we found that C1q was bound by an average of only 45% of the PMN analyzed. Further, these PMN were not dispersed in a normal log distribution, indicating some heterogeneity among the cells that bind C1q. We examined the abilities of the chemoattractant N-formylmethionylleucylphenylalanine (fMLP) and the phorbol ester phorbol dibutyrate (PDBu) to modulate expression of C1qR as compared to the receptor for C3b (CR1). Pretreatment of the monocytes and the PMN with either 10(-6)M fMLP or 10 ng/ml of PDBu significantly increased cell surface CR1 expression, as reported previously by other investigators. In contrast, no significant increase in the number of C1qR on the monocytes or the PMN was observed with any of the concentrations of fMLP or PDBu used during pretreatment. However, with certain pretreatment doses of these agents, some reduction was noted in the amount of 125I-C1q bound to the monocytes and the PMN. This study characterizes the binding of C1q to purified monocytes and confirms previously published values for PMN. The distribution of cells expressing C1qR is shown to be significantly different between identically treated populations of monocytes and PMN. Finally, the abilities of fMLP and PDBu to modulate the binding of C1qR are examined. Our results indicate that the control of C1qR expression differs markedly from that of CR1.

Binding Sites, Antibody↗
PubMed2000

Humoral autoreactivity directed against surfactant protein-A (SP-A) in rheumatoid arthritis synovial fluids.

SP-A is found principally in the lung, and has been associated with lamellar bodies also found in the synovial joint. Both SP-A and C1q contain collagen-like regions, and SP-A and C1q have some structural similarities, both having a globular head region and a collagen-like tail. Here we are able to show that (i) autoreactivity to SP-A, as expressed by IgG and IgM autoantibodies, is present in synovial fluid (SF) isolated from patients with rheumatoid arthritis (RA); (ii) in absorption experiments only a limited degree of cross-reactivity between autoantibodies reactive with C1q and SP-A is observed; (iii) there is no cross-reactivity between autoantibodies reactive with type II collagen (CII) and those reactive with SP-A or C1q; (iv) autoantibodies react with polymeric (dimers and larger) SP-A, but not with monomeric SP-A subunits, indicating that a degree of quaternary structure is required for antibody binding. Unlike CII, which not accessible in the normal joint, both SP-A and C1q are available within the SF in patients with RA and may therefore provide antigens driving an autoimmune response directed against collagen-like structures.

Animals↗
PubMed1982

Impaired phagocytic function and increased immune complexes in diabetics with severe microangiopathy.

An increase in circulating immune complexes (AgAb) of medium size has been observed in diabetics with late complications. This increase may be related either to an increased formation or reduced clearance. Alternatively, both mechanisms may be involved. As medium-sized AgAb determined by the C1q solid phase method are mainly removed from circulation by the fixed phagocytes of the reticulo-endothelial system, we investigated the function of these cells using a colloid clearance test in diabetics with various degrees of microangiopathy. Microaggregated iodinated human serum albumin was injected into 30 diabetic volunteers with severe (group 1), moderate (group 2), and absent (group 3) microangiopathy, and into 40 normal volunteers. The colloid clearance was significantly reduced in diabetics with severe microangiopathy in comparison with patients who had no sign of microangiopathy, or with normal subjects. A significant correlation was found between reduced colloid clearance and increased levels of circulating AgAb determined by C1q solid phase method. Results of this study suggest that the increase in circulating AgAb observed in patients with severe microangiopathy may result from an impaired function of mixed phagocytes.

Adult↗
PubMed1984

Potentiation of the antibody induced platelet aggregation in vitro.

The combined addition of a heterologous anti-human C1q serum and an anti-IgG-L-chain (kappa) serum to only once washed human platelets potentiates their aggregation in vitro in comparison to the effect of the same antisera alone. The biological significance of this process is discussed.

Antibodies↗
PubMed1988

Complement activation is not required for IgG-mediated suppression of the antibody response.

Feedback suppression of the antibody response by IgG is known to be dependent on intact Fc regions. However, it is not clear which of the Fc-mediated effector functions is required. In the present report we have studied whether ability or inability of the IgG antibodies to activate the complement system was of consequence for their immunosuppressive effect. First, a monoclonal IgG1-anti-2,4,6-trinitrophenyl (TNP) antibody, unable to activate complement via the classical or alternate pathway, was shown to be able to inhibit more than 90% of the in vivo sheep erythrocyte-specific antibody response in mice when TNP coupled to sheep erythrocytes was used as antigen. Second, we investigated the immunosuppressive ability of a non-complement-activating mutant IgG2a-anti-TNP monoclonal antibody. The mutant differs from the wild type by a single amino acid substitution in the CH2 domain leading to inability to fix complement factor C1q. However, the mutant has the same affinity for antigen and the same Fc receptor-binding capacity as the wild type antibody. It is demonstrated that the mutant was as efficient as the wild type antibody in inhibiting an in vitro antibody response to TNP-coupled sheep erythrocytes. These findings confirm the non-determinant specificity and Fc dependence of IgG-mediated suppression, and show that the Fc-mediated effector mechanism is independent of complement activation. The results instead suggest binding to Fc receptors as a necessary step in feedback immunosuppression and favor inactivation of B cells by cross-linking of Fc and antigen receptors on their surface rather than elimination of antigen by complement-dependent phagocytosis as the effector mechanism.

Animals↗
PubMed2003

C1q nephropathy: a variant of focal segmental glomerulosclerosis.

BACKGROUND: C1q nephropathy is a poorly understood and controversial entity with distinctive immunopathologic features. In order to better define the clinical-pathologic spectrum, we report the largest single-center series. METHODS: Nineteen biopsies with C1q nephropathy were identified from among 8909 native kidney biopsies received from 1994 to 2002 (0.21%). Defining criteria included (1). dominant or co-dominant immunofluorescence staining for C1q, (2). mesangial electron dense deposits, and (3). no clinical or serologic evidence of systemic lupus erythematosus (SLE). RESULTS: The 19 patients were predominantly African American (73.7%), female (73.7%), young adults and children (range, 3 to 42 years; mean, 24.2 years). Presentation included nephrotic range proteinuria (78.9%), nephrotic syndrome (50%), renal insufficiency (27.8%), and hematuria (22.2%). No patient had hypocomplementemia or evidence of underlying autoimmune or infectious disease. Renal biopsy revealed focal segmental glomerulosclerosis (FSGS) in 17 (including six collapsing and two cellular) and minimal-change disease (MCD) in two. All biopsies displayed co-deposits of immunoglobulin G (IgG), with more variable IgM (84.2%), IgA (31.6%), and C3 (52.6%). Foot process effacement varied from 20% to 100% (mean, 51%). Twelve of 16 patients with available follow-up received immunosuppressive therapy. One patient had complete remission of proteinuria and six had partial remission. Four patients with FSGS pattern had progressive renal insufficiency, including two who reached end-stage renal disease (ESRD). Median time from biopsy to ESRD was 81 months. On multivariate analysis, the best correlate of renal insufficiency at biopsy and at follow-up was the degree of tubular atrophy and interstitial fibrosis (P = 0.0495 and 0.0341, respectively). CONCLUSION: C1q nephropathy falls within the clinical-pathologic spectrum of MCD/FSGS. Although further studies are needed to determine the pathomechanism of C1q deposition, we hypothesize that it may be a non-specific marker of increased mesangial trafficking in the setting of glomerular proteinuria.

Adolescent↗
PubMed1991

Differentiation between neutrophil-bound antibodies and immune complexes.

It is often unknown whether neutrophil-bound immunoglobulins (NBIg) in patients with chronic diseases consist of bound immune complexes (IC) or of anti-neutrophil antibodies. Until now, the detection of IC in serum by the C1q-binding test has been used to define the nature of NBIg. Here we present studies on methods for characterization of NBIg using a bivalent IC and heat-aggregated IgG as IC models and neutrophil alloantibodies as antibody models. Heat-aggregated IgG was readily detected in the C1q-binding test. However, the bivalent IC, which is capable of binding to both low-affinity Fc receptors (FcRII and FcRIII) on neutrophils was not detected in this test. This was due to failure of the bivalent IC to bind to C1q, as was demonstrated by studies with immobilized C1q. However, the bivalent IC as well as heat-aggregated IgG, when bound to neutrophils from healthy donors, were not or only marginally eluted from the cell surface by lowering the pH, in contrast to a number of different cell-bound antibodies. This led to the observation that eluates, prepared from sensitized cells, showed reactivity with donor neutrophils, whereas eluates, prepared from cells to which immune complexes had bound, did not. Thus, a negative result in the C1q-binding test does not prove that a serum does not contain neutrophil-binding IC, but the reactivity of an eluate can distinguish between anti-neutrophil antibodies and bound IC.

Antigen-Antibody Complex↗
PubMed1988

Association of levels of circulating C1q binding macromolecules with induction chemotherapy response in head and neck cancer patients.

Ninety-five untreated patients with squamous cell carcinoma of the upper aerodigestive tract expressed significantly higher levels of C1q-binding macromolecules as compared to 45 noncancer-bearing controls. No relationship between C1q-binding macromolecules and levels of circulating IgG-immune complexes as determined by the solid-phase C1q-binding assay or the C3d-solid-phase assay could be defined suggesting that C1q-binding macromolecules were distinct from IgG-circulating immune complexes. An elevated level of C1q-binding macromolecules within these patients was predictive of subsequent response to induction chemotherapy; those with elevated levels characteristically showed no response. Using multivariate logistic regression analysis including the covariates of American Joint Committee staging parameters as well as C1q assay results, levels of the isolated macromolecules added significant prognostic information as to the probability of chemotherapeutic response. The quantitation of C1q macromolecules has clinical implication as to choice of therapeutic regimens against head and neck cancer. The nature of these substances remains to be defined.

Adult↗
PubMed1983

[Demonstration of circulating immune complexes using a C1q-solid phase enzyme immunoassay].

An enzyme-immunoassay for the quantitative determination of circulating immune complexes in human serum is described. The technique uses alkaline phosphatase-conjugated anti-human IgG to detect immune complexes bound to solid phase C1q. This assay is sensitive detecting 4 ng/ml to 60 micrograms/ml aggregated IgG. First data from normal individuals and patients with systemic lupus erythematosus show that this method is specific and sensitive for detection of circulating immune complexes.

Antigen-Antibody Complex↗
PubMed1981

An assay for antigen-antibody complexes in human sera using C1q-enzyme conjugates.

An assay for soluble immune complexes employing enzyme-C1q conjugates is described. The method is sensitive, rapid and precise, and should prove suitable for monitoring patients. The test gave positive results for complexes in normal pregnant women and indicated significantly increased levels in subjects with pre-eclampsia.

Antigen-Antibody Complex↗
PubMed1986

The metabolism of C1 inhibitor and C1q in patients with acquired C1-inhibitor deficiency.

The metabolism of 125I-labeled C1 inhibitor (C1INH) and C1q was studied in five patients with B cell lymphoproliferative disorders, C1INH deficiency, and angioedema. C1INH catabolism was markedly accelerated in these patients. The fractional catabolic rate (FCR) was 0.053 of the plasma pool per hour compared to that of normal subjects (0.025) or patients with hereditary angioneurotic edema (HANE) (0.035). The catabolism of two dysfunctional proteins Wel and Ta was studied. Protein Wel was catabolized at an accelerated rate (0.041) compared to that in patients with HANE (0.029) or in normal subjects (0.020). In contrast, the FCR of protein Ta was 0.012, which is similar to that in normal patients and in patients with HANE. The extravascular to plasma ratio (E/P) of the normal C1INH in patients was 1.55 compared to 0.60 in normal patients. This is consistent with the rapid extravascular sequestration of the C1INH. The synthesis rate of the C1INH was 0.29 mg/kg/hr in patients that is similar to that in control subjects. The metabolism of C1q was studied in two normal control subjects and three patients. The FCR of C1q was 0.051 in patients compared to 0.023 in control subjects. The E/P was increased in patients (2.8) compared to E/P in control subjects (0.6). The acquisition of C1INH deficiency results from increased consumption of C1INH in vivo.

Adult↗