Thrombin in the Activation of the Fluid Contact Phase in Patients with Hereditary Angioedema Carrying the F12 P.Thr309Lys Variant

Hereditary angioedema due to pathogenic FXII variants (HAE-FXII) is a rare dominant disease caused by increased activation of the plasma contact system. The most prevalent HAE-FXII variant, c.1032C > A p.Thr309Lys (FXII^309Lys), results in a smaller FXII protein with increased sensitivity to fluid-phase activation by poorly understood mechanisms. We aimed to investigate the functionality of the FXII^309Lys variant in 33 HAE-FXII patients, 25 healthy controls and 46 patients with congenital disorders of glycosylation (CDG). Activation of the plasma contact system was assessed by western blot and amidolytic assay in basal conditions or after treatment with either artificial or physiological activators. Recombinant wild-type and FXII^309Lys variants were expressed in S2 insect (Drosophila) cells. Amidolytic and fibrin generation assays were performed in fresh plasma samples. FXII^309Lys samples exhibited an increased electrophoretic mobility comparable with N-glycan-deficient FXII from CDG patients and asialo-FXII generated by neuraminidase treatment. They presented increased sensitivity to activation by dextran sulphate and silica which resulted in the generation of an aberrant 37-kDa heavy chain. We did not observe increased susceptibility of FXII^309Lys to proteolysis by exogenous or tPA-generated plasmin. However, both exogenous and endogenous thrombin cleaved the FXII^309Lys variant, releasing a 37-kDa fragment and resulting in enhanced proteolytic activation on the fluid phase. This model supports a sequential proteolytic activation process involving thrombin priming of FXII^309Lys, followed by kallikrein cleavage and generation of active βFXIIa. The present results and the observation that angioedema episodes in HAE-FXII patients occur predominantly during hypercoagulable situations suggest a key role for thrombin.

Serum properdin consumption as a biomarker of C5 convertase dysregulation in C3 glomerulopathy

Properdin (P) stabilizes the alternative pathway (AP) convertases, being the only known positive regulator of the complement system. In addition, P is a pattern recognition molecule able to initiate directly the AP on non-self surfaces. Although P deficiencies have long been known to be associated with Neisseria infections and P is often found deposited at sites of AP activation and tissue injury, the potential role of P in the pathogenesis of complement dysregulation-associated disorders has not been studied extensively. Serum P levels were measured in 49 patients with histological and clinical evidence of C3 glomerulopathy (C3G). Patients were divided into two groups according to the presence or absence of C3 nephritic factor (C3NeF), an autoantibody that stabilizes the AP C3 convertase. The presence of this autoantibody results in a significant reduction in circulating C3 (P < 0·001) and C5 levels (P < 0·05), but does not alter factor B, P and sC5b-9 levels. Interestingly, in our cohort, serum P levels were low in 17 of the 32 C3NeF-negative patients. This group exhibited significant reduction of C3 (P < 0·001) and C5 (P < 0·001) and increase of sC5b-9 (P < 0·001) plasma levels compared to the control group. Also, P consumption was correlated significantly with C3 (r = 0·798, P = 0·0001), C5 (r = 0·806, P < 0·0001), sC5b-9 (r = -0·683, P = 0·043) and a higher degree of proteinuria (r = -0·862, P = 0·013). These results illustrate further the heterogeneity among C3G patients and suggest that P serum levels could be a reliable clinical biomarker to identify patients with underlying surface AP C5 convertase dysregulation.

Laboratory guidelines for the diagnosis and follow-up of patients with monoclonal gammopathies

We present guidelines from the Immunochemistry group of the Spanish Society for Immunology that are designed to provide a practical tool for the diagnosis and follow-up of monoclonal gammopathies. We review the clinical and analytical features of various monoclonal gammopathies, international consensus guidelines and techniques used to detect and follow-up monoclonal components.

C1 inhibitor function using contact-phase proteases as target: evaluation of an innovative assay

BACKGROUND

Controlling prekallikrein activation by C1 inhibitor (C1Inh) represents the most essential mechanism for angioedema patient protection. C1Inh function in the plasma is usually measured based on the residual activity of the C1s protease not involved in the pathological process. We have hereby proposed an alternative enzymatic measurement of C1Inh function based on contact-phase activation and correlation with angioedema diagnostic requirements.

METHODS

The contact phase was reconstituted using the purified components, with C1Inh standard or plasma sample. The kinetics of the amidase activity were monitored using Pro-Phe-Arg-pNA, independently of alpha2-macroglobulin. We prevented any interference from a possible high plasma kininogenase activity by preincubating the samples with protease inhibitor. Receiver operating characteristics (ROC) were used to calculate the assay's diagnostic performance.

RESULTS

The calibration curve was built using C1Inh standard (threshold limit 0.10 × 10(-3) U, i.e., 0.2 pmol), and C1Inh function was quantified in the sample, with a reference interval established based on healthy individuals (n = 281; men: 0.61-1.10 U/ml, median: 0.85 U/ml; women: 0.42-1.08 U/ml, median: 0.74 U/ml). The median values of female donors were lower than those of the others due to estrogen, yet C1Inh function remained within the reference interval. The ROC curve calculation provided the following optimum diagnostic cutoff values: women 0.36 U/ml (area under curve [AUC]: 0.99; sensitivity: 93.48%; specificity: 99.37%); and men 0.61 U/ml (AUC: 1; sensitivity: 100.0%; specificity: 100.0%).

CONCLUSION

The performance outcome provided features suitable for angioedema diagnostic or follow-up. Established by means of the kinin formation process, this assay should be preferred over the method based on a C1s protease target.

Clinical Pattern and Acute and Long-term Management of Hereditary Angioedema Due to C1-Esterase Inhibitor Deficiency

BACKGROUND

Hereditary angioedema due to C1-esterase inhibitor deficiency (HAE-C1-INH) is a life-threatening disease.

OBJECTIVES

To describe the clinical characteristics and management of patients with HAE-C1-INH during routine clinical practice.

METHODS

An observational, retrospective study was performed in patients with HAE-C1-INH. Demographic, clinical, and analytical data were collected from 2 periods: period A (October 2009-September 2010) and period B (October 2007-September 2009).

RESULTS

We studied 112 patients with HAE-C1-INH (57.1% females). Age at onset of symptoms was 14.4 years (lower in patients who had experienced attacks in the previous year). In period B (n=87), 62.1% of patients presented at least 1 edema attack (median, 3.5 attacks/patient/2 years), and 19.1% of attacks were treated. In period A (n=77), 58.4% of patients were on maintenance therapy. Stanozolol was the most widely used drug (48.9%), with a mean weekly dose of 6.7 mg. At least 1 attack was recorded in 72.7% of patients (median, 3.0 attacks/patient/year), and 31.5% of the attacks were treated. Treatment of acute attacks increased by 12.4%.

CONCLUSION

Age at onset of symptoms is associated with clinical expression of disease. The higher age at onset of symptoms, the fewer number of attacks per patient and year, and the lower dose of attenuated androgens necessary to control the disease than in other series lead us to hypothesize that HAE-C1-INH could have a less severe expression in Spain. Acute attacks seem to be treated increasingly often.

A novel method for direct measurement of complement convertases activity in human serum

Complement convertases are enzymatic complexes that play a central role in sustaining and amplification of the complement cascade. Impairment of complement function leads directly or indirectly to pathological conditions, including higher infection rate, kidney diseases, autoimmune- or neurodegenerative diseases and ischaemia-reperfusion injury. An assay for direct measurement of activity of the convertases in patient sera is not available. Existing assays testing convertase function are based on purified complement components and, thus, convertase formation occurs under non-physiological conditions. We designed a new assay, in which C5 blocking compounds enabled separation of the complement cascade into two phases: the first ending at the stage of C5 convertases and the second ending with membrane attack complex formation. The use of rabbit erythrocytes or antibody-sensitized sheep erythrocytes as the platforms for convertase formation enabled easy readout based on measurement of haemolysis. Thus, properties of patient sera could be studied directly regarding convertase activity and membrane attack complex formation. Another advantage of this assay was the possibility to screen for host factors such as C3 nephritic factor and other anti-complement autoantibodies, or gain-of-function mutations, which prolong the half-life of complement convertases. Herein, we present proof of concept, detailed description and validation of this novel assay.

Consensus statement on the diagnosis, management, and treatment of angioedema mediated by bradykinin. Part I. Classification, epidemiology, pathophysiology, genetics, clinical symptoms, and diagnosis

BACKGROUND

There are no Spanish guidelines or consensus statement on bradykinin-induced angioedema.

AIM

To review the pathophysiology, genetics, and clinical symptoms of the different types of bradykinin-induced angioedema and to draft a consensus statement in light of currently available scientific evidence and the experience of experts. This statement will serve as a guideline to health professionals.

METHODS

The consensus was led by the Spanish Study Group on Bradykinin-Induced Angioedema (SGBA), a working group of the Spanish Society of Allergology and Clinical Immunology. A review was conducted of scientific papers on different types of bradykinin-induced angioedema (hereditary and acquired angioedema due to C1 inhibitor deficiency, hereditary angioedema related to estrogens, angioedema induced by angiotensin-converting enzyme inhibitors). Several discussion meetings of the SGBA were held in Madrid to reach the consensus.

RESULTS

The pathophysiology, genetics, and clinical symptoms of the different types of angioedema are reviewed. Diagnostic approaches are discussed and the consensus reached is described.

CONCLUSIONS

A review of bradykinin-induced angioedema and a consensus on diagnosis are presented.

Consensus statement on the diagnosis, management, and treatment of angioedema mediated by bradykinin. Part II. Treatment, follow-up, and special situations

BACKGROUND

There are no previous Spanish guidelines or consensus statements on bradykinin-induced angioedema.

AIM

To draft a consensus statement on the management and treatment of angioedema mediated by bradykinin in light of currently available scientific evidence and the experience of experts. This statement will serve as a guideline to health professionals.

METHODS

The consensus was led by the Spanish Study Group on Bradykinin-Induced Angioedema, a working group of the Spanish Society of Allergology and Clinical Immunology. A review was conducted of scientific papers on different types of bradykinin-induced angioedema (hereditary and acquired angioedema due to C1 inhibitor deficiency, hereditary angioedema related to estrogens, angioedema induced by angiotensin-converting enzyme inhibitors). Several discussion meetings were held to reach the consensus.

RESULTS

Treatment approaches are discussed, and the consensus reached is described. Specific situations are addressed, namely, pregnancy, contraception, travelling, blood donation, and organ transplantation.

CONCLUSIONS

A review of and consensus on treatment of bradykinin-induced angioedema is presented.

C7 deficiency and meningococcal infection susceptibility in two spanish families

In this work, we report the genetic basis of C7 deficiency in two different Spanish families. In family 1, by using exon-specific polymerase chain reaction and sequencing, a recently described mutation was found in homozygosity in the patient; a single base change in exon 15 (C2107T) leading to a stop codon that causes truncation of the C-terminal portion of C7 (Q681X). Patient's father, mother and sister were heterozygous for this mutation. Interestingly, patient's parents were not related. In family 2, a new single base mutation in exon 2 (G90A), leading to a stop codon that causes the premature truncation of C7 (W8X), was found in the patient, mother and sister 1. Additionally, patient 2, her father and sisters, displayed a missense mutation in exon 9 (G1135C) resulting in a change of aminoacid (G357R). Although sister 1 bore the same mutations in the C7 gene that patient 2, she remains asymptomatic. Because both mutations were found in the patient and her sister, we analyse other defence mechanisms such as FcgammaR polymorphisms as well as mannose-binding lectin alleles (MBL2 gene) and MBL levels. Results showed that both siblings bore identical combinations of FcgammaR allotypes and different MBL2 alleles, exhibiting patient 2 a MBL-insufficient genotype. Normal MBL levels were found in patient 1 and in two previously studied C7-deficient siblings, suggesting the involvement of other mechanisms of immunity distinct of FcgammaR variants and the MBL pathway, for the absence of meningococcal recurrent infections in certain C7-deficient individuals.

Successful renal transplantation in a patient with atypical hemolytic uremic syndrome carrying mutations in both factor I and MCP

Kidney transplantation in patients with atypical hemolytic uremic syndrome (aHUS) carrying mutations in the soluble complement regulators factor H (CFH) or factor I (CFI) is associated with elevated risk of disease recurrence and almost certain graft loss. In contrast, recurrence is unusual in patients with mutations in the membrane-associated complement regulator membrane cofactor protein (MCP) (CD46). Therefore, a panel of experts recently recommended the combined liver-kidney transplantation to minimize aHUS recurrence in patients with mutations in CFH or CFI. There was, however, very limited information regarding transplantation in patients carrying mutations in both soluble and membrane-associated complement regulators to support a recommendation. Here, we report the case of an aHUS patient with a heterozygous mutation in both CFI and MCP who received an isolated kidney transplant expressing normal MCP levels. Critically, the patient suffered from a severe antibody-mediated rejection that was successfully treated with plasmapheresis and IvIgG. Most important, despite the complement activation in the allograft, there was no evidence of thrombotic microangiopathy, suggesting that the normal MCP levels in the grafted kidney were sufficient to prevent the aHUS recurrence. Our results suggest that isolated kidney transplantation may be a good first option for care in aHUS patients carrying CFI/MCP combined heterozygous mutations.

Functional analysis in serum from atypical Hemolytic Uremic Syndrome patients reveals impaired protection of host cells associated with mutations in factor H

A subgroup of patients with the most severe form of the Hemolytic Uremic Syndrome (HUS) presents mutations in the complement regulatory protein factor H. The functional analyses of the factor H mutant proteins purified from some of these patients have shown a specific defect in the capacity to control complement activation on cellular surfaces. Here, we show that these factor H-related complement regulatory defects can be detected in the patients' serum with a simple hemolytic assay. Data obtained from HUS patients and control individuals indicate that this assay is a useful tool for the molecular diagnosis of factor H-related HUS.

Complement component C7 deficiency in a Spanish family

Different genetic mutations have been described in complement component C7 deficiency, a molecular defect which is clinically associated with an increased susceptibility to neisserial recurrent infections, although some cases remain asymptomatic. In this work we report the genetic bases of C7 deficiency in one Spanish family. Exon-specific PCR and sequencing revealed a novel point mutation at nucleotide 615 (exon 6) leading to a stop codon (UGG to UGA) in the patient, his mother, and sister. This transversion causes the premature truncation of the C7 protein (W183X). Additionally, we detected a missense mutation at position 1135 (exon 9) located in the first nucleotide of the codon GGG (CGG), resulting in an amino acid change (G357R) in the patient, his father, as well as in his sister. This latter mutation had been previously described in individuals from Moroccan Sephardic Jewish ancestry. Since both heterozygous mutations were found in the patient as well as in his asymptomatic sister, we analyse other meningococcal defence mechanisms such as polymorphisms of the opsonin receptors on polymorphonuclear cells. Results showed that the patient and his sister bore identical combinations of FcgammaRIIA-H/R131 and FcgammaRIIIB-NA1/2 allotypes. Our results provide further evidence that the molecular pathogenesis of C7 deficiency as well as susceptibility to meningococcal disease are heterogeneous, since different families carry different molecular defects, although many of the C7 defects appear to be homogeneous in individuals from certain geographical areas. The missense mutation G357R would make an interesting topic of analysis with regard to meningococcal disease susceptibility in the Spanish population.

Complement factor I deficiency associated with recurrent meningitis coinciding with menstruation

BACKGROUND

Complement (C) factor I deficiency is a rare immunodeficiency state frequently associated with recurrent pyogenic infections in early infancy. This deficiency causes a permanent uncontrolled activation of the alternative pathway resulting in massive consumption of C3.

PATIENT

A 23-year-old woman with monthly recurrent meningitis episodes, mostly in the perimenstrual period, since August 1999. Previously, at age 16 years, she had meningococcal sepsis, also coinciding with menstruation.

OBJECTIVES

To study the patient and her family to elucidate the molecular defects in the pedigree and to evaluate her clinical evolution.

RESULTS

We describe clinical, immunological, and treatment follow-up during this period. First, we characterized the existence of a total complement factor I deficiency defined by undetectable levels by enzyme immunosorbent assay. This total deficiency was also found in her sister. Her parents and brother had approximately half of the normal levels. In addition, the patient had very low levels of C3; factor B; and an important reduction of factor H, properdin, C5, C7, and C8 complement components. Additional studies in the patient's sera evidenced high levels of immune complexes containing C1q and immunoglobulin (Ig) G, as well as C3b/factor H, C3b/properdin, C3b/IgG, and properdin/IgG complexes. Treatment with prophylactic antibiotics, antiestrogen medication, plasma infusions, or intravenous immunoglobulin has been unsuccessful in avoiding consecutive meningitis episodes.

CONCLUSION

For the first time to our knowledge, these data present an unusual relationship between meningitis episodes and menstruation in factor I immunodeficiency.

Clustering of missense mutations in the C-terminal region of factor H in atypical hemolytic uremic syndrome

Hemolytic-uremic syndrome (HUS) is a microvasculature disorder leading to microangiopathic hemolytic anemia, thrombocytopenia, and acute renal failure. Most cases of HUS are associated with epidemics of diarrhea caused by verocytotoxin-producing bacteria, but atypical cases of HUS not associated with diarrhea (aHUS) also occur. Early studies describing the association of aHUS with deficiencies of factor H suggested a role for this complement regulator in aHUS. Molecular evidence of factor H involvement in aHUS was first provided by Warwicker et al., who demonstrated that aHUS segregated with the chromosome 1q region containing the factor H gene (HF1) and who identified a mutation in HF1 in a case of familial aHUS with normal levels of factor H. We have performed the mutational screening of the HF1 gene in a novel series of 13 Spanish patients with aHUS who present normal complement profiles and whose plasma levels of factor H are, with one exception, within the normal range. These studies have resulted in the identification of five novel HF1 mutations in four of the patients. Allele HF1 Delta exon2, a genomic deletion of exon 2, produces a null HF1 allele and results in plasma levels of factor H that are 50% of normal. T956M, W1183L, L1189R, and V1197A are missense mutations that alter amino acid residues in the C-terminal portion of factor H, within a region--SCR16-SCR20--that is involved in the binding to solid-phase C3b and to negatively charged cellular structures. This remarkable clustering of mutations in HF1 suggests that a specific dysfunction in the protection of cellular surfaces by factor H is a major pathogenic condition underlying aHUS.

Internalization of factor J and cellular signalization after factor J-cell interaction

Factor J (FJ) is a cationic glycoprotein with inhibitory activity in vitro against both classical and alternative pathways of complement activation. Recently FJ has been implicated in adhesion to several cell lines, through a membrane receptor identified as nucleolin. In the present work we study the events that follow the binding of FJ to cells. After incubation of K562 with FJ, this protein was internalized actively and localized in the cytoplasm and nucleus. Adhesion to immobilized FJ induced tyrosine phosphorylation of several intracellular proteins in Jurkat cell line with a similar pattern to that induced by fibronectin (FN), an extracellular matrix protein. This effect was maximal at 5 min and decreased after 10 min, and inhibited by anti-FJ monoclonal antibody (mAb). These results suggest that the binding of FJ to cells may play an important role in transduction of biochemical signals across the plasma membrane to the cell interior.

A novel nonsense mutation at Glu-631 in a Spanish family with complement component 7 deficiency

Deficiency of the seventh component of complement (C7D) is frequently associated with recurrent neisserial infections. We report in the present study the genetic basis for C7D in a Spanish family. We used exon-specific polymerase chain reaction (PCR)/single-strand conformation polymorphism (SSCP) analysis as a screening step for mutations, followed by direct sequencing of the target exon. The mutation in the proband was a homozygous G-to-T transversion at nucleotide 1957, the first nucleotide of the codon GAG for Glu-631, leading to a stop codon TAG (E631X). Our result provides further evidence that the molecular pathogenesis of C7D is heterogeneous.

Cellular adhesion mediated by factor J, a complement inhibitor. Evidence for nucleolin involvement

Factor J (FJ) is a complement inhibitor that acts on the classical and the alternative pathways. We demonstrated FJ-cell interactions in fluid phase by flow cytometry experiments using the cell lines Jurkat, K562, JY, and peripheral blood lymphocytes. FJ bound to plastic plates was able to induce in vitro adhesion of these cells with potency equivalent to fibronectin. As evidence for the specificity of this reaction, the adhesion was blocked by MAJ2, an anti-FJ monoclonal antibody, and by soluble FJ. Attachment of the cells required active metabolism and cytoskeletal integrity. The glycosaminoglycans heparin, heparan sulfate, or chondroitin sulfates A, B, and C inhibited to varying degrees the binding of FJ to cells, as did treatment with chondroitinase ABC. In the search for a putative receptor, a protein of 110 kDa was isolated by affinity chromatography, and microsequence analysis identified this protein as nucleolin. Confocal microscopy evidenced the presence of nucleolin in cell membrane by immunofluorescence with monoclonal (D3) and polyclonal anti-nucleolin antibodies in Jurkat cells. The interaction FJ-nucleolin was evidenced by Western blot and enzyme-linked immunosorbent assay. Furthermore, purified nucleolin and D3 inhibited adhesion of Jurkat cells to immobilized FJ, suggesting that the interaction was specific and that nucleolin mediated the binding.

Elevated factor J levels in synovial fluid from patients with inflammatory arthropathies

Factor J (FJ) is a complement inhibitor that is able to regulate in vitro both the classical and alternative human complement pathways. In the search of its biological significance, we have analyzed FJ levels in synovial fluid from patients with different arthropathies, in which IL-6 levels had been previously measured. The pathologies included in this study were: rheumatoid arthritis (RA) (n = 21), crystal deposition diseases (CDD) (n = 6), osteoarthritis (OA) (n = 23), spondyloarthritis (SpA) (n = 3) and other inflammatory arthropathies (OIA) (n = 4). We found a good correlation between IL-6 and FJ levels (r = 0.33, p = 0.0132) in the 57 processed samples. Synovial fluids had high levels of IL-6 (median: 3000 pg/ml). Besides, we found that FJ levels were elevated (241 +/- 429 micrograms/ml) when compared with NHS (5.32 +/- 2.82 micrograms/ml). Considering OA patients as control group for non-inflammatory situation, we found that FJ levels were significantly elevated in inflammatory patients only if RA patients were excluded. Furthermore, there were also significant differences with CDD patients. In addition, we have examined the presence of this inhibitor in synovial fluid by Western blot after running gels at acid pH and electrophoretical transference at the same pH. In these experiments, we evidenced the presence of a cationic protein immunoreactive with polyclonal and monoclonal anti-FJ antibodies. In conclusion, FJ levels are elevated in pathological synovial fluids. FJ could be an acute phase reactant as other molecules present in the synovial fluid, or could be shed from extracellular matrix as a consequence of the high enzymatic activity present in the articular fluid or as a response to the inflammatory stimulus.

Modulation of C4b-binding protein isoforms during the acute phase response caused by orthopedic surgery

Orthopedic surgery is described as an event with a high risk of thromboembolic diseases. This is probably a consequence of a synergistic combination of different risk factors in the patients subjected to this type of surgery, including age, immobilization, anesthesia and different hypercoagulable states. After surgery patients develop an acute-phase response that leads to changes in several plasma proteins. One of these proteins is the complement regulator C4b-binding protein (C4BP). We have recently shown that in some acute-phase patients C4BP is incorrectly controlled (with elevation of the C4BP beta-containing isoforms), leading to a potential hypercoagulable state by decreasing the plasma levels of free (active) protein S. Here we have studied whether patients subjected to orthopedic surgery have an appropriate modulation of the C4BP isoforms during their postoperative acute-phase responses. We have analyzed the evolution of the C4BP isoforms in serial samples from 11 patients who have undergone knee (or hip) prosthesis surgery (mean age 70 years), or scoliosis surgery (mean age 18 years). Our data suggest a similar evolution of C4BP isoforms in all these patients, with an almost exclusive increase of C4BP isoforms lacking C4BP beta polypeptides and steady levels of free protein S.

Factor J, an inhibitor of the classical and alternative complement pathway, does not inhibit esterolysis by factor D

Factor J (FJ) is an inhibitor of the classical and alternative complement pathways. On the classical pathway factor J disrupts the C1 component, and on the alternative pathway, factor J disrupts the C3 convertase (C3b,Bb) by a direct interaction of FJ with the components C3b and Bb. The aim of this work was to verify whether FJ could have any effect on factor D proteolytic activity since previous experiments could not rule out an eventual inhibition by factor J on factor D enzymatic activity. For this purpose, the reactivity of serine proteinase factor D was determined by using two peptide thioester substrates, Z-Lys-SBzl.HCl and Z-Lys-Arg-SBzl.2HCl, in the presence and in the absence of factor J. Kinetic studies evidenced that FJ did not affect the enzymatic activity of factor D in any case.

Cell surface molecules related to factor J in human lymphoid cells and cell lines

Factor J (FJ) is a cationic glycoprotein that is able to inhibit in vitro both the classical and alternative pathways of complement. FJ was purified to homogeneity from human urine by sequential chromatographic steps. To examine the expression of FJ in human cells we obtained mAbs against urine-purified FJ. Preliminary studies by immunocytochemistry revealed that one of the anti-FJ mAbs recognized cell surface components of certain cell lines, such as K562 and U937 cells, so we have focused subsequently on the detection of these homologue membrane-bound FJ Ags (FJ-h Ags) in cell lines of lymphoid (Ramos and Jurkat) and mieloyd (U937 and K562) origin, as well as in peripheral blood cells. The flow cytometry analysis of the examined cell lines revealed partial staining ranging from 10% (U937) to 29% (K562) positive cells. Flow cytometry of peripheral blood cells showed a positive staining in a small but consistent population of lymphocytes (mean = 11%, n = 17) but none at all on monocytes, granulocytes, erythrocytes, or platelets. Double Ab immunostaining of lymphocytes showed that the FJ-h positive population included mainly B lymphocytes (a mean of 63% CD19+ were FJ-h positive). When we analyzed peripheral blood lymphocytes from a patient with chronic lymphocytic leukemia B (95% CD19+/CD5+), the majority of these (55%) bore FJ-h on their surface. Acid strip of these cells did not abrogate the surface staining, which supports the finding that the Ag is tightly bound to the membrane. Immunoprecipitation from U937 cell lysates showed a single 65 kDa band under reducing conditions. FJ-h Ags purified from K562 and U937 cells displayed inhibitory activity in the functional EAC14 assay for the classical complement pathway, as did urine FJ, and they were recognized immunochemically by five different (one polyclonal and four monoclonal) anti-FJ Abs. In conclusion, FJ-homologues are present in the membranes of several human cell lines that show functional and antigenic characteristics similar to soluble urine FJ. They are also found in a small subset of peripheral blood lymphocytes, mainly B cells. The structural relationship between both soluble urine FJ and these membrane-bound FJ-h remains to be established.

Cell surface molecules related to factor J in human lymphoid cells and cell lines

Factor J (FJ) is a cationic glycoprotein that is able to inhibit in vitro both the classical and alternative pathways of complement. FJ was purified to homogeneity from human urine by sequential chromatographic steps. To examine the expression of FJ in human cells we obtained mAbs against urine-purified FJ. Preliminary studies by immunocytochemistry revealed that one of the anti-FJ mAbs recognized cell surface components of certain cell lines, such as K562 and U937 cells, so we have focused subsequently on the detection of these homologue membrane-bound FJ Ags (FJ-h Ags) in cell lines of lymphoid (Ramos and Jurkat) and mieloyd (U937 and K562) origin, as well as in peripheral blood cells. The flow cytometry analysis of the examined cell lines revealed partial staining ranging from 10% (U937) to 29% (K562) positive cells. Flow cytometry of peripheral blood cells showed a positive staining in a small but consistent population of lymphocytes (mean = 11%, n = 17) but none at all on monocytes, granulocytes, erythrocytes, or platelets. Double Ab immunostaining of lymphocytes showed that the FJ-h positive population included mainly B lymphocytes (a mean of 63% CD19+ were FJ-h positive). When we analyzed peripheral blood lymphocytes from a patient with chronic lymphocytic leukemia B (95% CD19+/CD5+), the majority of these (55%) bore FJ-h on their surface. Acid strip of these cells did not abrogate the surface staining, which supports the finding that the Ag is tightly bound to the membrane. Immunoprecipitation from U937 cell lysates showed a single 65 kDa band under reducing conditions. FJ-h Ags purified from K562 and U937 cells displayed inhibitory activity in the functional EAC14 assay for the classical complement pathway, as did urine FJ, and they were recognized immunochemically by five different (one polyclonal and four monoclonal) anti-FJ Abs. In conclusion, FJ-homologues are present in the membranes of several human cell lines that show functional and antigenic characteristics similar to soluble urine FJ. They are also found in a small subset of peripheral blood lymphocytes, mainly B cells. The structural relationship between both soluble urine FJ and these membrane-bound FJ-h remains to be established.

The inhibitory effect of factor J on the alternative complement pathway

Factor J (FJ) is a cationic glycoprotein with inhibitory activity in C1, the first component of the classical complement pathway. This study demonstrates that FJ is able to regulate the activity of the alternative complement pathway. FJ inhibits the generation of fluid-phase and cell-bound alternative pathway C3 convertase, C3b,Bb (C3-cleaving enzyme). Thus, FJ interferes with the generation of alternative pathway C3 convertase when sheep erythrocytes bearing antibody and activated C3 and C4 (EAC4b,3b) are incubated with the individual complement components, factors B, D, and P. FJ accelerates the decay of C3 convertase with a time course similar to that of factor H, and when both regulators are present together, the decay of enzyme activity is faster than when they are added separately. Furthermore, FJ is able to inhibit the cleavage of C3 by factor B in a fluid-phase assay. FJ prevents the initiation of alternative pathway activation in "more stabilized systems" with well known activators of alternative pathway C3 convertase such as C3 nephritic factor (an autoantibody against alternative pathway C3 convertase), cobra venom factor, and rabbit erythrocytes. In these systems, FJ has no effect on C3 convertase stabilized by rabbit erythrocytes or cobra venom factor. In contrast, FJ promotes the dissociation of C3 convertase stabilized by C3 nephritic factor, but with much lower efficiency than in preventing initiation. Direct interaction of FJ with individual components of C3 convertase was shown by a solid-phase binding assay using plates coated with C3, C3b, B, Bb, or FJ. FJ inhibitory activity in the alternative pathway can be modulated by polyanions like heparin. FJ-mediated inhibition in the alternative complement pathway can be modified by surface interactions, as occurs during alternative pathway C3 convertase activation. Thus, when FJ is adsorbed by and eluted from hydroxylapatite and reverse-phase columns, its inhibitory effect on more stabilized systems is lost. This loss of inhibitory activity is fully reversed when FJ is rechromatographed on heparin-Sepharose or Sepharose columns. Taking into account these data, FJ may be included in the group of highly charged molecules that inhibit the activation of classical and alternative complement pathways (i.e. eosinophil major basic protein, protamine, and heparin).

Factor J, a human inhibitor of complement C1, is a cationic, highly glycosylated protein

Factor J (FJ) is a new inhibitor of the complement system. This work supports the fact that FJ is a cationic molecule (pI > or = 9.6 in native conditions, or pI = 8.1 in denaturing conditions) with a high sugar content (40%) that is able to interact with different lectins, suggesting a complex glycosylation. SDS impaired FJ migration in polyacrylamide gel electrophoresis. In Triton-acid-urea-polyacrylamide gel electrophoresis FJ migrated as a complex, dispersed molecule. In contrast, FJ after Smith degradation (dFJ) gave a single, smeared band of M(r) = 23.4 kDa in reducing SDS-PAGE. dFJ retained only 60% of the initial inhibitory activity of intact FJ. When digestions with different proteinases were performed, no modification of activity was observed. After beta-glucuronidase digestion, FJ lost 80% of its initial activity. Consequently, glycosylation plays an important role in the inhibitory activity of FJ.

Factor J, an inhibitor of the complement classical pathway: the quantitation by an ELISA inhibition assay in normal human serum

Factor J (FJ) is a protein present in human serum, with inhibitory activity against C1. Here we describe the quantitation of FJ in human serum by means of an ELISA inhibition assay. We have purified FJ from the urine of a normal donor following a previously published method with slight modifications. Polyclonal anti-FJ antibodies have been raised in rabbits immunized with a single dose of purified antigen injected in multiple sites. IgG from polyclonal FJ antiserum, coupled to a solid matrix (Affi-Prep gel) was able to adsorb purified FJ antigenically and functionally. Furthermore, anti-FJ specifically retained serum components antigenically related with urine FJ. Taking into account this reactivity, we have developed an inhibition enzyme-linked immunosorbent assay (ELISA) useful for measuring FJ levels in normal human serum. This immunoassay involves preincubating polyclonal anti-FJ with different dilutions of normal human serum to quantitatively reduce the antibody available to bind to purified FJ-coated microtiter plates. Binding of remaining antibody to the microtiter plate is measured spectrophotometrically using peroxidase-conjugated secondary antibody. Quantitation is accomplished by comparison with a known quantity of purified FJ. Conditions for optimization of this quantitative assay have been assessed, including trials with different blocking agents, of which nonfat milk gave the best results. Preliminary experiments showed the existence of paradoxical effects, that is, high nonspecific binding at high serum dilutions. We have eliminated these effects by including high ionic strength (0.4 M NaCl) in the sample incubation solution. Sensitivity and reproducibility parameters have also been established. FJ levels have been measured for the first time in sera from 86 healthy donors.(ABSTRACT TRUNCATED AT 250 WORDS)

Requirements for the production of high-titre C3 nephritic factor (NEF) antibody in vitro

C3 nephritic factor (NEF) is an IgG autoantibody directed against neoantigenic determinants of the alternative C3 convertase (C3b.Bb). Structural and functional studies require important amounts of this antibody, which are difficult to obtain from patients' sera. We have developed a method for increasing NEF production in vitro. Epstein-Barr virus is a herpes virus which transforms B lymphocytes. Some authors were able to induce the production of NEF in vitro after infection with Epstein-Barr virus (EBV). These works were preformed without any previous cellular selection of B cells. We have performed a method of preselecting antigen-binding cells prior to EBV transformation. Non-preselected cells yielded 0.16 U/million cells in culture (U/M) of NEF antibody, whereas enriched cells for NEF antibody in eliminated 8 U/M (sheep erythrocytes coated with anti-IgG, A, M). Specific NEF synthesis can be increased, in peripheral blood mononuclear cells (PBMC) from patients by in vitro stimulation with the antigens recognized by NEF [C3b.Bb, 21,000 MW protein from patients' E membranes and 26,000 MW protein from sheep E membranes (ShE)]. The highest stimulation is induced by the C3b.Bb and by 26,000 MW protein, 21,000 MW protein had lowest stimulatory effect. In this work also we have shown that patients having NEF antibody in sera have an increase of the CD5-CD19 subset, when compared with the controls.

Autoantibodies in patients with IgA and IgG2 deficiencies

Patients with primary immunodeficiencies have a high incidence of autoantibodies, mainly of no clinical significance. It has recently been suggested that patients with a combined IgA-IgG2 deficiency have more autoantibodies than those patients with isolated deficiencies. We have studied 42 patients with selective IgA deficiency, nine with isolated IgG2 deficiency and 13 with combined IgA-IgG2 deficiency, and have found that the combined IgA-IgG2 deficiency has no influence on autoantibody prevalence, except for anti-IgA antibodies. The presence of chronic respiratory infections (a clinical feature commonly associated with both selective IgA and IgG2 deficiencies) is unrelated to the prevalence of autoantibodies. The most frequent autoantibodies found are anti-IgA and anti-cardiolipin. Most of the autoantibodies have been found to be devoid of actual clinical significance. Only three patients had overt autoimmune disease.

Familial incidence of C3 nephritic factor

C3 nephritic factor (NEF) has been found in 3 siblings presenting different (or none) degrees of renal disease. Other relatives, including their dead father, suffered from a renal illness. In 2 of the siblings, NEF activity was restricted to IgG1 and IgG3 subclasses. Familial NEF incidence and a shared C3 allotype and a common HLA haplotype including BfS alleles for the 3 NEF-positive siblings suggest that at least in our cases genetical factors may be involved in NEF generation.

Interaction of C3 nephritic factor (NEF) with erythrocyte membranes complement-independent binding to sheep and patients' erythrocytes

Complement-independent binding of C3 nephritic factor (NEF) to sheep erythrocytes was observed in heat-inactivated sera from patients having this autoantibody. The binding was observed after neuraminidase treatment of erythrocytes but not following trypsin treatment. Purified IgG from patients' sera was able to bind to ShE membranes. Binding to rat and rabbit erythrocytes was also observed but not to human group O+ erythrocytes. By Western blot NEF ab recognizes a 26 kD protein on the sheep erythrocytes and a 21 kD protein on human erythrocytes. NEF activity decreased at these positions when blotted nitrocellulose was incubated with NEF antibody. This autoantibody binds human erythrocytes membranes from patients but not from 55 normal blood donors. IgG from a pool from 10 different controls did not bind membrane E from the patients. The amino acid analysis of the 21 kD protein of the patients showed differences in basic residues (Arg and Lys) when compared with the 21 kD protein obtained from controls. N-terminal sequence analysis indicated that it is blocked in both proteins.

Determination of C3 nephritic factor activity by a microassay based on the peroxidase-like activity of the heme group

We report a modification of a method for measuring the C3 nephritic factor, using the peroxidase activity of the heme group. This modification increases the sensitivity of the method, approximately seven-fold when NEF activities are measured in U/mL. It is less time-consuming and it allows the simultaneous testing of a larger number of samples, simplifying the screening of sera and ensuring an easy and simple test for the detection of NEF in purification processes as well as in in vitro production. The method could also be useful in other hemolytic assays.

Incidence of selective IgG2 deficiency in patients with vasculitis

IgG2 deficiency has been recently associated with the appearance of vasculitis. None of the 42 patients with IgG2 deficiency whom we studied has a history of vasculitis. We have also studied 56 patients with vasculitis, and found four of them with IgG2 levels below the normal range for their age. As a group, the vasculitis patients did not differ in the incidence of low IgG2 levels from a normal population. Three of the four vasculitis patients with low IgG2 levels had a Henoch-Schonlein syndrome, and the association between both features was statistically significant.

Interaction between C3 nephritic factor and erythrocyte membranes. Presence of nephritic factor in patients' erythrocytes

The presence of IgG has been observed by fluorescence microscopy in the erythrocytes of 5 patients with NEF antibody. IgG subclass distribution of the IgG bound was analyzed by fluorescence-activated cell sorter. NEF activity was also determined in the eluted antibodies from the erythrocyte membrane. Three of five patients had NEF antibody bound to the erythrocyte membrane. IgG subclass distribution of NEF antibody sera was also investigated by means of protein A-Sepharose and using monoclonal antibodies against human IgG subclasses. NEF activity was mediated by IgG3 alone in 3 patients and by a combination of IgG1 and IgG3 in 2 patients.

C3 nephritic factor determination. A comparison between two methods

C3 nephritic factor (NEF), an IgG autoantibody to the alternative pathway C3 convertase, is usually measured by crossed immunoelectrophoresis (CI) but recently a reliable haemolytic assay (HA) was described by Rother (1982). This method is more specific than CI because it is negative in sera with immune complexes, SLE and sera incubated with IgG aggregates. The haemolytic assay is sensitive enough to detect NEF antibody in serum from patients with only slightly low C3 levels and NEF negatives by CI. The haemolytic assay is easy to perform and reproducible, the interassay coefficient of variation being 10.7% compared to 64% in the CI. The intra-assay coefficient of variation in CI was 28% compared to 5.5% in the haemolytic assay. The haemolytic method enabled us to study the kinetic effects of NEF on C3b.Bb bound to sheep erythrocytes, and the lysis mediated by ShE.C3b.Bb.NEF complex. Also the C and NEF binding to sheep erythrocytes was studied.

Evidence of an immediate hypersensitivity mechanism in systemic lupus erythematosus

In 30 patients with systemic lupus erythematosus the number of a circulating basophils was countered in different stages of activity. An inverse correlation was found between the absolute basophils count and anti-DNA antibodies and presumptive circulating immune complexes (as judged by polyethylene glycol precipitation of serum). A positive correlation was found between the absolute basophil count and C3 or C4 levels. IgE on the basophil surface was determined by radioimmunoassay in 7 patients. All of them showed a significantly higher surface IgE number. When the count of circulating basophils was roughly normal, 5 out of the 6 patients showed a positive basophil degranulation test with native DNA. These results suggest the existence of an anti-DNA specific IgE in lupus patients. Depression of the circulating basophil count may be a useful index of lupus activity.