Immunoradiometric assay for human complement component C9 utilising monoclonal antibodies

The rare C9 P167S risk variant for age-related macular degeneration increases polymerization of the terminal component of the complement cascade

Age-related macular degeneration (AMD) is a complex neurodegenerative eye disease with behavioral and genetic etiology and is the leading cause of irreversible vision loss among elderly Caucasians. Functionally significant genetic variants in the alternative pathway of complement have been strongly linked to disease. More recently, a rare variant in the terminal pathway of complement has been associated with increased risk, Complement component 9 (C9) P167S. To assess the functional consequence of this variant, C9 levels were measured in two independent cohorts of AMD patients. In both cohorts, it was demonstrated that the P167S variant was associated with low C9 plasma levels. Further analysis showed that patients with advanced AMD had elevated sC5b-9 compared to those with non-advanced AMD, although this was not associated with the P167S polymorphism. Electron microscopy of membrane attack complexes (MACs) generated using recombinantly produced wild type or P167S C9 demonstrated identical MAC ring structures. In functional assays, the P167S variant displayed a higher propensity to polymerize and a small increase in its ability to induce hemolysis of sheep erythrocytes when added to C9-depleted serum. The demonstration that this C9 P167S AMD risk polymorphism displays increased polymerization and functional activity provides a rationale for the gene therapy trials of sCD59 to inhibit the terminal pathway of complement in AMD that are underway.

Recombinant aequorin as a probe for cytosolic free Ca2+ in Escherichia coli

We describe a novel and simple method for the measurement of bacterial cytosolic free calcium ([Ca2+]i) using recombinant aequorin reconstituted within live bacterial cells. Using this method we have measured the effects of external calcium, complement, phagocytosis and antibiotics on the [Ca2+]i of Escherichia coli. In principle this method should be applicable to any genetically transformable organism and should suffer fewer problems than fluorescent dyes for subcellular calcium measurement.

A double-blind controlled trial of high dose methylprednisolone in patients with multiple sclerosis: 2. Laboratory results

Laboratory measurements were compared in paired samples from 50 patients included in a double-blind placebo controlled trial of methylprednisolone in the treatment of multiple sclerosis. Cerebrospinal fluid total cell count, IgG and C9 indices, and percentage of peripheral blood OKT8 positive cells were abnormal at entry and returned closer to the normal range after active than placebo treatment, but the differences were not statistically significant. The percentage of peripheral blood OKT4 positive cells was normal at entry as was the amplitude of visual evoked potentials, whereas their latency was prolonged; these measurements were each uninfluenced by methylprednisolone. Corticosteroids might act merely by influencing oedema, but the laboratory results suggest that methylprednisolone affects immunological events which underly rapid onset and recovery of symptoms in patients with multiple sclerosis; additional forms of treatment are needed to maintain these clinical and immunological effects.

Complement component C9 in Graves' disease

C9, the terminal component of complement, is the key part of the membrane attack complex formed as a result of complement activation; it has also been reported to be an acute phase protein. Its potential role in Graves' disease has been studied by measuring plasma C9 concentrations using an automated two-site immunoradiometric assay employing monoclonal antibodies, whose binding to thyroid tissue has also been investigated. The plasma C9 concentration in patients with hyperthyroid Graves' disease (86.3 +/- 21.6 mg/l, mean +/- SD; n = 49) was significantly increased (P less than 0.001) compared with normal subjects (60.4 +/- 13.4 mg/l; n = 48). In contrast, the plasma concentration of C-reactive protein, a marker of the acute phase response, was not significantly different between the two groups. The plasma C9 concentration in patients with hyperthyroid Graves' disease decreased significantly (P less than 0.01) after treatment with antithyroid drugs (carbimazole or methimazole; n = 14), but not after radioactive iodine (131I) treatment (n = 18). Immunohistochemical staining demonstrated that monoclonal antibody to C9 bound to the basement membranes of thyroid follicular cells of Graves' thyroid tissue but not to normal thyroid tissue. Radiolabelled monoclonal antibody to C9 bound to membrane fragments prepared from thyroid glands from two patients with Graves' disease. We conclude that C9, and by implication the membrane attack complex, may be involved in the pathogenesis of Graves' disease.

Monoclonal antibodies demonstrate protection of polymorphonuclear leukocytes against complement attack

Studies on erythrocytes have shown that the formation of the membrane attack complex on a cell surface inevitably results in lysis. However, it is known that nucleated cells are much more difficult to kill with complement, although the molecular basis of this resistance has never been established. We have shown that a very early intracellular event, occurring within seconds of formation of the attack complex in the membrane, is a rise in cytoplasmic Ca2+, which can activate cell responses without cell death 5,6. Here we report the use of a monoclonal antibody to the terminal complement component C9, quantified by 125I and visualized by fluorescein, to demonstrate a protection mechanism in polymorphonuclear leukocytes (PMNs) attacked by complement, involving removal of the attack complex by vesiculation. Concomitantly, there is a Ca2+-dependent activation of reactive oxygen metabolite production without cell lysis. These findings have important implications in the evolutionary and pathological significance of the terminal components of the complement pathway.

Measurement of C9 concentrations using an immunochemiluminometric assay

A 2-site immunochemiluminometric assay is described for the measurement of complement component C9 concentrations in biological fluids as an aid in the diagnosis and management of immune-based diseases. The assay utilises 2 monoclonal antibodies one of which is labelled with a chemiluminescent acridinium ester and one of which is covalently coupled to reprecipitated aminoaryl cellulose. The incubation time is 1 h with simultaneous reagent addition. The working range of the assay is 10-2500 micrograms/1 at CVs less than or equal to 10% and the results are in excellent agreement with those of an immunoradiometric assay. The assay exhibits superior performance to other immunochemical and immunoassay techniques and has the advantage of using stable, non-radioactive reagents.

Covert cross reactants in a two-site immunoassay studied with monoclonal antibodies

A one-step two-site immunoradiometric assay for the measurement of free beta subunit of human chorionic gonadotrophin (beta-hCG) was developed using monoclonal antibodies. The immobilized antibody was specific for free beta subunit and the radiolabeled antibody recognized both intact human chorionic gonadotrophin (hCG) and free beta subunit. Although the level of hCG "cross-reaction" was low when studied using conventional techniques, the apparent beta-hCG content of samples was found to be inversely proportional to the hCG level. From both experimental evidence and computer simulation studies this was found to be due to the binding of hCG to the limited amount of 125I-labeled antibody present. The term covert cross reactants has been introduced to describe substances which bind to only one of the antibodies in a two-site immunoassay. When establishing such an assay the effect of covert cross reactants on the response of an analyte should be investigated.

Terminal component of complement (C9) in cerebrospinal fluid of patients with multiple sclerosis

An immunoradiometric assay was used to measure the concentration of the terminal component of complement (C9) in cerebrospinal fluid (CSF) and plasma from 35 patients with multiple sclerosis and 55 controls with other neurological diseases. There was a highly significant reduction in cerebrospinal fluid C9 concentration in patients with multiple sclerosis (0.26 +/- 0.02 microgram/ml) compared with controls (1.52 +/- 0.20 micrograms/ml; p less than 0.0005). As a single protein measurement C9 seemed to be more useful as an aid to clinical diagnosis than CSF IgG; the C9 index was also a better discriminator than IgG index between the two groups of patients. Reduced CSF C9 concentration in patients with multiple sclerosis implies C9 consumption due to formation of membrane attack complexes, which could mediate myelin damage and cause more widespread but reversible loss of function, accounting for the transient symptoms characteristic of the disease.

Construction of a new family of high efficiency bacterial expression vectors: identification of cDNA clones coding for human liver proteins

Construction of a family of bacterial expression vectors, pEX1-3, is described. These vectors are derived from a cro-lacZ gene fusion plasmid which expresses large quantities of fusion protein under the control of the PR promoter of bacteriophage lambda. A polylinker has been engineered into the 3' end of the lacZ gene in all three translational reading frames, and stop signals for transcription and translation inserted, so that any open reading frame DNA may be expressed as a hybrid beta-galactosidase protein. cDNA fragments cloned in these vectors can be detected with an efficiency of greater than 1 in 3, thus enabling the detection of rare cDNA molecules. In addition, the low solubility of hybrid proteins leads to a rapid isolation procedure allowing antibodies of pre-determined specificity to be made against expressed regions of cloned DNA. We describe the cloning of albumin and complement C9 genes from a human cDNA library using polyclonal and monoclonal antibodies.

Inhibition of complement-induced [14C]sucrose release by intracellular and extracellular monoclonal antibodies to C9: evidence that C9 is a transmembrane protein

Monoclonal antibodies to the terminal component of the human complement pathway, C9 were used to inhibit the complement-induced release of entrapped [14C]sucrose from erythrocyte ghosts. Antibodies were present either outside, or entrapped within the ghosts. Different monoclonal antibodies were demonstrated to inhibit [14C]sucrose release depending on whether the antibody was outside or entrapped within the ghosts. These findings demonstrate that C9 within the membrane attack complex on erythrocyte membranes is an asymmetrical transmembrane protein penetrating into the cytoplasmic space.