Development and clinical application of electroimmunoassays for the direct quantification of the complement C3 split products C3c and C3d

Daily monitoring of viral load measured as SARS-CoV-2 antigen and RNA in blood, IL-6, CRP and complement C3d predicts outcome in patients hospitalized with COVID-19

OBJECTIVES

We hypothesized that the amount of antigen produced in the body during a COVID-19 infection might differ between patients, and that maximum concentrations would predict the degree of both inflammation and outcome for patients.

METHODS

Eighty-four hospitalized and SARS-CoV-2 PCR swab-positive patients, were followed with blood sampling every day until discharge or death. A total of 444 serial EDTA plasma samples were analyzed for a range of biomarkers: SARS-CoV-2 nuclear antigen and RNA concentration, complement activation as well as several inflammatory markers, and KL-6 as a lung marker. The patients were divided into outcome groups depending on need of respiratory support and death/survival.

RESULTS

Circulating SARS-CoV-2 nuclear antigen levels were above the detection limit in blood in 65 out of 84 COVID-19 PCR swab-positive patients on day one of hospitalization, as was viral RNA in plasma in 30 out of 84. In all patients, complete antigen clearance was observed within 24 days. There were definite statistically significant differences between the groups depending on their biomarkers, showing that the concentrations of virus RNA and antigen were correlated to the inflammatory biomarker levels, respiratory treatment and death.

CONCLUSIONS

Viral antigen is cleared in parallel with the virus RNA levels. The levels of antigens and SARS-CoV-2 RNA in the blood correlates with the level of IL-6, inflammation, respiratory failure and death. We propose that the antigens levels together with RNA in blood can be used to predict the severity of disease, outcome, and the clearance of the virus from the body.

Effect of modified ultrafiltration on the inflammatory response in paediatric open-heart surgery: a prospective, randomized study

Modified ultrafiltration (MUF) is often used in conjunction with paediatric cardiac surgery with cardiopulmonary bypass (CPB) and is thought to improve clinical outcome. It is unclear whether these improvements (if any) are due to the removal of inflammatory mediators. In this prospective study, 18 children aged 12-24 months undergoing uncomplicated cardiac surgery with methylprednisolone added in the pump prime were randomized to receive CPB with ( n= 10) and without ( n= 8) MUF. Cytokines (TNFα, IL-6, IL- 1β, IL-10, IL-1ra), complement split products (C3d, C4d) and coagulation system activation (F1+ 2, ATIII) were measured pre-, peri- and up to 48 h postoperatively. For clinical outcome, the alveolar-arterial oxygen (A-a) gradient, transfusion requirement, drain loss, mean blood pressure and requirement for inotropic support were registered up to 24 h postoperatively. Our results show an improvement in postoperative oxygenation as well as a tendency towards decreased drain loss and improved haemodynamics in the MUF group. There were no intergroup differences detectable for TNFα, IL-1β, IL-1ra, complement and coagulation markers. We conclude that MUF in itself does not significantly influence TNFα, IL-1β, IL-1ra and the complement and coagulation profiles in children undergoing cardiac surgerywith CPB. Despite this, there was some evidence for improved clinical outcome. Our results do not support that MUF improves postoperative organ function by modulation of the measured markers of inflammation.

Plasma concentrations of complement split product C3d and immune complexes after procainamide induced production of antinuclear antibodies

Seventeen patients treated with procainamide for cardiac ventricular arrhythmias were followed for up to 40 weeks. Immunological data as a clue to developing the systemic lupus erythematosus (SLE)-like syndrome was emphasized. Ten patients developed antinuclear antibodies (IgG or IgM), but no increase in the plasma concentration of the complement split product C3d or immune complexes, measured by two different methods, was demonstrated. This finding is in contrast to the high levels of both C3d and immune complexes in SLE. The discrepancy may be caused by a lack of immune complex mediated complement activation by the procainamide induced antibodies, or may be due to a difference in severity of disease. The acetylator phenotype of the patients was determined but due to the low frequency of fast acetylators no comparison of the immunological response of the two phenotypes could be done.

Phase I Safety, Tolerability, and Pharmacokinetic Study of Recombinant Human Mannan-Binding Lectin

Mannan-binding lectin (MBL), a human plasma protein, plays an important role in the innate immune defence. MBL recognizes microorganisms through surface carbohydrate structures. Due to genetic polymorphisms, MBL plasma concentrations range from 5 to 10,000 ng/mL. Approximately 30% of the human population have low levels of MBL (below 500 ng/mL). MBL deficiency is associated with increased susceptibility to infections in immunosuppressed individuals, e.g., during chemotherapeutically induced neutropenia. Replacement therapy with MBL may be beneficial in this patient group, and recombinant human MBL (rhMBL) is in development as a novel therapeutic approach. To assess the safety, tolerability, and pharmacokinetics of rhMBL, a placebo-controlled double-blinded study was performed in MBL-deficient healthy male subjects. rhMBL was administered as both single intravenous (i.v.) infusions (0.01, 0.05, 0.1, and 0.5 mg/kg) and repeated i.v. infusions (0.1 or 0.3 mg/kg given at 3-day intervals). There were no difference in incidence and type of adverse events reported in the study between the groups of subjects receiving rhMBL and the placebo group. All adverse events reported as drug-related were mild and no serious adverse events were recorded. There were no clinically significant changes in laboratory evaluations, ECG or vital signs, and no anti-MBL antibodies were detected following rhMBL administration. After single i.v. doses of rhMBL the maximal plasma levels increased in a dose-dependent manner reaching a geometric mean of 9710 ng/mL+/-10.5% in the highest dose group (0.5 mg/kg), with an elimination half-life of approximately 30 h. No rhMBL accumulation in plasma was observed following repeat dosing. Administration of rhMBL restored the ability to activate the MBL pathway of the complement system without non-specific activation of the complement cascade. In conclusion, no safety or tolerability concern was raised following rhMBL administration no signs of immunogenicity detected, and an rhMBL plasma level judged sufficient to achieve therapeutic benefit (>1000 ng/mL) can be achieved.

Streptokinase, complement activation and hypotension

The purpose of this study was to establish whether complement activation is the cause of transient hypotension during streptokinase infusion in patients with acute myocardial infarction. Thirteen patients with suspected acute myocardial infarction and treated with streptokinase were included. Complement 3d (C3d) as an indicator of complement activation was assessed in venous blood and blood pressure was measured. Ten patients had verified myocardial infarction. Three patients did not. Five patients developed an increase in C3d blood levels of more than 200% within 30 min. All patients developed a transient fall in blood pressure during infusion of streptokinase. This was related neither to presence of myocardial infarction nor to degree of complement activation. The mechanism of hypotension observed following the administration of streptokinase is not through complement activation, and thus how streptokinase induces hypotension is still obscure.

Mannan-binding protein forms complexes with alpha-2-macroglobulin. A protein model for the interaction

We report that alpha-2-macroglobulin (alpha 2M) can form complexes with a high molecular weight porcine mannan-binding protein (pMBP-28). The alpha 2M/pMBP-28 complexes was isolated by PEG-precipitation and affinity chromatography on mannan-Sepharose, protein A-Sepharose and anti-IgM Sepharose. The occurrence of alpha 2M/pMBP-28 complexes was further indicated by crossed immunoelectrophoresis and by use of an anti-alpha 2M affinity column and chelating Sepharose loaded with Zn2+. The eluates from these affinity columns showed alpha 2M subunits (94 and 180 kDa) and pMBP subunits (28kDa) in SDS-PAGE, which reacted with antibodies against alpha 2M and pMBP-28, respectively, in Western blotting. Furthermore, alpha 2M/pMBP-28 complexes were demonstrated by electron microscopy. Fractionation of pMBP-containing D-mannose eluate from mannan-Sepharose on Superose 6 showed two protein peaks which reacted with anti-C1 s antibodies in ELISA, one of about 650-800 kDa, which in addition contained pMBP-28 and anti-alpha 2M reactive material, the other with an M(r) of 100-150 kDa. The latter peak revealed rhomboid molecules (7 x 15 nm) in the electron microscope and a 67 kDa band in SDS-PAGE under reducing conditions. This band was also seen in eluates from the anti-alpha 2M and chelating Sepharose columns. Based on these observations and previous findings by other investigators of a serine protease with about 67 kDa subunits which copurifies with human MBP we propose a model for the interaction of pMBP-28 with alpha 2M.

Protease-antiprotease levels and whole-blood chemiluminescence in acute peritonitis

Whole-blood chemiluminescence and levels of leukocyte proteases and plasma protease inhibitors were studied in 43 patients with acute, generalized peritonitis. An almost three-fold increase in whole-blood chemiluminescence was found in acute peritonitis, which may indicate activation or "priming" of the leukocytes by blood-borne factors. High levels of leukocyte elastase and neutrophil proteinase 4(3) were found in plasma and peritoneal exudate. Patients with sepsis had higher plasma levels of both proteases than other patients. Large variations in the plasma levels among patients decreased their sensitivity as markers of infectious complications during the postoperative period. The plasma levels of the protease inhibitors followed three different patterns of reaction. The acute phase proteins alpha 1-proteinase inhibitor and C1-inactivator, increased during the first week of disease, to normalise later in its course. alpha 2-macroglobulin, antithrombin III and alpha 2-antiplasmin were all decreased from onset and normalised later in the course, while secretory leukocyte protease inhibitor showed a slow decrease throughout the course of disease. In peritonitis exudate, the levels of the main protease inhibitors, alpha 1-Proteinase Inhibitor and alpha 2-Macroglobulin, were decreased, probably due to complexation and subsequent elimination, as a part of the defense against liberated leukocyte proteases. The immunoreactive and especially functional levels of the protease inhibitors alpha 2-Antiplasmin, Antithrombin III and C1-Inactivator were also decreased in the exudate, indicating an increased turn-over of these proteins through activation of the cascade systems and/or break-down by leukocyte proteases. In contrast to the other inhibitors, secretory leukocyte protease inhibitor showed higher levels in exudate than in plasma, and unexpectedly high exudate/plasma-quotients were seen in cases with colonic perforations. Degradation of complement factor 3 (C3) and decreased "opsonic capacity" were found in exudate. The "opsonic capacity" could be correlated to the levels of leukocyte proteases in the exudate, which indicates that degradation of complement factor 3 may have been at least partly due to the action of leukocyte proteases. Further depletion of complement factors in exudates of long-standing peritonitis or abscesses may create a vicious circle of deficient opsonisation and clearance of bacteria, as earlier reported for chronic pleural exudates.

Influence of plasma proteinase inhibitors and the secretory leucocyte proteinase inhibitor on pancreatic elastase-induced degradation of some plasma proteins

Pancreatic elastase-induced degradation of some plasma proteins was studied in an in vitro model. The digestion was correlated with the degree of saturation of the alpha 1-proteinase inhibitor (alpha 1PI) and also with varying amounts of secretory leucocyte proteinase inhibitor (SLPI). SLPI was found to inhibit pancreatic elastase showing a Ki of about 10(-7) M for the complex. On the addition of human pancreatic elastase to plasma cleavage of C3, kininogen, fibrinogen and fibronectin was observed when the alpha 1PI approached saturation. In the present in vitro model it was possible to block the cleavage of the four plasma proteins, mentioned above completely with SLPI. Addition of the inhibitor also decreased the consumption of alpha 1PI.

C3 activation products, C3 containing immune complexes, the terminal complement complex and native C9 in patients with rheumatoid arthritis

Complement activation products, C9 and C3-containing circulating immune complexes (CIC), were evaluated in plasma and synovial fluid (SF) from patients with rheumatoid arthritis (RA) and osteoarthritis. C3 activation products and the fluid phase terminal complement complex were considerably elevated in SF from RA patients reaching levels five- to eighttimes that in plasma, consistant with a local activation of the whole cascade in the joints. The results emphazise the importance of detecting C3 activation by neoepitope expression instead of single fragment determinations. The concentration of native C9 was lower in synovial fluid compared with plasma, consistant with the excessive local complement activation. Increased CIC levels which correlated with the degree of complement activation were also found in the SF from the RA patients.

Comparative study of assays detecting complement activation. Complement-split product C3d (rocket immuno-electrophoresis) and C3d neodeterminants (ELISA)

The aim of the study was to investigate the correlation between two types of assay measuring specific products of complement C3 activation and their clinical application. Complement C3d split product was estimated using double-decker rocket immunoelectrophoresis (DD-RIE) and measurements of C3d neodeterminants exposed after C3 activation was carried out with an enzyme-linked immunosorbent assay (ELISA). A total of 595 blood samples were measured in parallel in the DD-RIE and the ELISA test systems. The samples originated from blood donors (44), uraemic patients undergoing dialysis (135), serial samples from rheumatoid arthritis (RA) patients during steroid treatment (88) and 328 randomly collected patient samples. The mean values for DD-RIE and ELISA (+/- 1 SD) for the 595 samples were 48 (+/- 20) mU/l and 48 (+/- 28) mU/l respectively. The interassay coefficient of variation (CV) in the ELISA was 18%. The Spearman rho-correlation coefficient between the two assays was 0.63 for all 595 samples. The mean values using ELISA and DD-RIE were practically identical for the 328 successively incoming samples, the samples from the 135 dialysis patients and the 44 donors. In RA patients a higher mean value was found for the 88 samples using DD-RIE than ELISA. In the majority of patient samples there was a good correlation between the two assays. However, the ELISA appears to be more sensitive in detecting acute complement activation and to give lower levels in RA patients with chronic complement activation.

Effect of amnionitis on the complement system of preterm infants

The development of the complement system was studied by quantitation of total hemolytic complement activity (CH50), C1q, C3, C4, and C3 split product (C3d) in cord plasma of nine human fetuses (17-22 weeks of gestation), 110 preterm (24-36 weeks of gestation) and 30 term neonates. The complement levels were analyzed in relation to various illnesses of preterm infants. Histological examination of the placenta revealed a higher incidence of amnionitis in the placenta of less than 34 gestational weeks. In cases without amnionitis, there were significant correlations between complement levels and gestational age. In cases with amnionitis, the complement system was activated even in infants of less than 28 weeks gestation. The complement levels correlated with the extent of the inflammation in the placentas and umbilical cords except for C1q. In infants with Wilson-Mikity syndrome, complement levels other than C1q were significantly elevated in comparison with those of infants with respiratory distress syndrome. In the group of preterm infants without amnionitis, no differences were found between infants with intrauterine growth retardation and those with growth appropriate for gestational age.

Hereditary, complete deficiency of complement factor H associated with recurrent meningococcal disease

Complement factor H (beta-1H globulin) is an important regulatory protein which inhibits the spontaneous complement activation via the alternative pathway. We describe a 15-year-old girl without any detectable factor H in plasma. She has had two episodes of meningococcal disease, but is otherwise completely healthy. Secondary to the factor-H deficiency, the levels of factor B, properdin, C3, and C5-C9 were strongly reduced due to spontaneous in vivo activation of the alternative complement pathway. Plasma C3dg was strongly elevated in spite of the factor-H deficiency; apparently erythrocyte CR1 substitutes for factor H in C3 degradation. Neither C3 nor complement lesions were demonstrable on her erythrocytes which did, however, show increased, spontaneous haemolysis in vitro in citrate plasma, but not in serum. The patient is a single child and her parents, who are unrelated and healthy, had half-normal levels of factor H. This reduction of factor H is sufficient to cause increased, spontaneous activation of the alternative pathway.

Changes in PMN leukocyte migration activity and complement C3d levels in RA patients with high disease activity during steroid treatment

We have investigated chemotaxis of polymorphonuclear granulocytes (PMN) from 7 well characterized RA patients with intense disease activity, before and after steroid treatment. Increased spontaneous and directed granulocyte migration was observed in 6 out of 7 patients before steroid treatment. In 5 patients these parameters were reduced after treatment. In contrast to this, decreased chemotaxis of polymorphonuclear granulocytes (PMN) from patients with Rheumatoid Arthritis (RA), have been reported earlier. This has been suggested as a partial explanation of the increased morbidity of these patients. Plasma levels of Complement C3d were initially increased in all patients and were slightly reduced following treatment. PMN migration in highly active RA cases is increased and responds markedly to steroid treatment, in contrast to the complement activation. The mainly unaffected, increased levels of plasma C3d might, in part, explain the early recurrence of symptoms often seen when steroid medication is withdrawn. Our results contrast with earlier findings and need to be confirmed in further studies.

Abnormal proteolysis (DIC)--successful treatment with antithrombin III concentrate and a concentrate containing F XIII and native von Willebrand factor

Two patients with life-threatening disseminated intravascular coagulation (DIC) syndrome, one caused by Gram-negative bacteria and one by premature separation of the placenta, are described. Specific substitution was given by antithrombin III concentrate and AHF-Kabi, a low purity factor VIII concentrate containing native von Willebrand factor and factor XIII. The treatment quickly returned the extremely low levels of antithrombin III, factor VIII:C, fibrinogen and factor XIII, initially found, to normal, and also returned the multimeric pattern of von Willebrand factor to normal. This resulted in diminished bleeding, enabling surgical treatment of the underlying disease.

Influence of plasma protease inhibitors and the secretory leucocyte protease inhibitor on leucocyte elastase-induced consumption of selected plasma proteins in vitro in man

Cleavage of C3, fibronectin, antithrombin III and alpha 2-antiplasmin in human plasma following the addition of increasing amounts of human leucocyte elastase was studied using an in vitro model. The cleavage was correlated with the degree of saturation of the plasma protease inhibitors alpha 2-macroglobulin and alpha 1-protease inhibitor and also with varying amounts of secretory leucocyte protease inhibitor. When alpha 1-protease inhibitor approached saturation, there was a prompt cleavage of all the four plasma proteins studied. The secretory leucocyte protease inhibitor was needed in a concentration of 6 mumol/l in the present model to block this consumption completely. This concentration also gave some protection of alpha 1-protease inhibitor and alpha 2-macroglobulin.

Characterization of a monoclonal antibody MoAb bH6 reacting with a neoepitope of human C3 expressed on C3b, iC3b, and C3c

Activation products of the complement cascade contain neoepitopes that are not present in the individual native components. Monoclonal antibodies detecting neoepitopes have been used for direct quantification of activation at different steps in the cascade. These methods are suggested to be more sensitive and reliable than conventional complement activation tests, which are hampered by precipitation or fractionation procedures. The present study describes production screening and characterization of a monoclonal antibody (MoAb) bH6. MoAb bH6 exhibited a significantly higher binding capacity to ELISA plates coated with zymosan-activated human serum than to plates coated with EDTA plasma. When fixed to the enzyme-linked immunosorbent assay (ELISA) plates, MoAb bH6 retained material from zymosan-activated serum that only reacted with anti-C3 antibodies. Crossed immunoelectrophoresis performed on zymosan-activated serum demonstrated that MoAb bH6 co-precipitated with anti-C3c antibodies. In experiments using highly purified cell-bound fragments MoAb bH6 showed reactivity with C3b and iC3b, but not with C3d. MoAb bH6 reacted in ELISA with purified C3c, but not with C3dg, both as capture antibody and in tests with the fragments absorbed to the solid phase. Thus, MoAb bH6 is highly specific for a neoepitope of human C3 expressed on the cleavage fragments of C3b, iC3b, and C3c.

Quantification in enzyme-linked immunosorbent assay of a C3 neoepitope expressed on activated human complement factor C3

A sensitive double antibody enzyme-linked immunosorbent assay (ELISA) for quantification of C3 activation products in human plasma, synovial fluid, and cerebrospinal fluid is described. The monoclonal antibody MoAb bH6, which is specific for a C3 neoepitope expressed on C3b, iC3b, and C3c, was used as capture antibody. Detection antibody was a polyclonal rabbit anti-human C3c followed by development with a peroxidase-conjugated anti-rabbit Ig antiserum. The activity in normal human EDTA plasma was 1.5% of that in zymosan-activated serum (ZAS). The interassay and intra-assay coefficients of variation were 15% and 3%, respectively. The lower detection limit was 0.0005% of the ZAS standard. Reference range (1.1-2.1% of ZAS) was obtained by measuring EDTA plasma from 40 healthy blood donors. A positive correlation rs = +0.92; P less than 0.0002) was found between the present assay and an already established C3'g' activation ELISA, when samples from 16 patients were examined in both assays simultaneously. The present assay and an assay detecting the terminal complement complex showed virtually identical activation patterns in consecutively drawn samples from a patient undergoing extracorporal circulation.

Lumbar disc surgery and variations in C-reactive protein, erythrocyte sedimentation rate and the complement split product C 3 d

Lumbar disc surgery was performed in fifty consecutive patients and variation in erythrocyte sedimentation rate (ESR), complement C 3 d, and C-reactive protein (CRP) levels before and after surgery were recorded. Preoperative values were within normal limits in all patients. Postoperatively, CRP increased immediately, with a maximum of 28.5 mg/l on the 2nd day and were normalized within 6 days. The maximum ESR elevation occurred after the 6th day and was followed by a slow decrease. After 12 weeks some patients still had an elevated ESR. Plasma C 3 varied pari passu with the ESR. Uncomplicated recovery after lumbar disc surgery seems to be indicated by a normalization of CRP, regardless of ESR values. Therefore, ESR may not be so useful as an indicator of disc space inflammation as previously accepted.

The quantitation of C3d by routine methods after the direct absorption of human plasma with anti-C3c

The immunological methods for quantitating C3d in plasma require first the removal of less fragmented intermediates as well as the intact C3. We describe an alternative method for the quantitation of C3d in human plasma. The components which should be removed are absorbed (precipitated) directly in the plasma by a specific anti-C3c antiserum. It is then possible to determine the concentration of C3d by routine immunological methods.