Complement deficiency and disease

C2 deficiency in blood donors and lupus patients: prevalence, clinical characteristics and HLA-associations in the Brazilian population

The objective of the present study was to investigate the prevalence, clinical characteristics, and HLA association of C2 deficiency in the Brazilian population. The frequency of C2 deficiency profile (C2Q degree profile) was 2.2% among 1503 blood donors and 6.6% among 166 patients with systemic lupus erythematosus (SLE). A higher incidence of clinical manifestations possibly related to immune complex disease was observed among blood donors with C2Q degree profile and their relatives with C2Q degree profile when compared to the normal C2 relatives. The comparison of clinical and laboratory features between SLE patients with C2Q degree profile and those with normal C2 revealed earlier disease onset, higher frequency of oral ulcerations and lower frequency of anti-native DNA antibodies in the first group. The HLA study conducted on 18 individuals with C2Q degree profile (11 blood donors and 7 SLE patients) confirmed the previously reported association with the antigens HLA-A25, B18 and DR2, supporting the concept that probably most C2 deficiency cases, throughout the world, are due to a single mutation in the C2 gene in linkage disequilibrium with the A25B18DR2 haplotype.

Molecular basis of hereditary C1q deficiency associated with SLE and IgA nephropathy in a Turkish family

Two siblings (case 1 and case 2) with homozygous C1q deficiency are described. Both presented with a photosensitive rash, and during follow-up case one developed SLE with nephrotic range proteinuria. Case 2 had microscopic hematuria with a past history of macroscopic hematuria. Renal biopsies revealed mesangioproliferative glomerulonephritis in case 1 and IgA nephropathy in case 2, a new finding in association with C1q deficiency. Since the classical pathway of complement plays a role in the development of antibody responses, the family was also evaluated for the immune response to hepatitis B vaccine. Antibody response to hepatitis B vaccine was normal in both affected members and the rest of the family. The A-, B- and C- chain genes of C1q were amplified by PCR and directly sequenced. A homozygous C to T point mutation was identified in genomic DNA isolated from the patients at codon 186 in the A chain that resulted in a premature stop codon. This mutation was present in both parents and both unaffected sibs in the heterozygous state. This mutation was identical to that previously described in a Slovakian family with C1q deficiency. Because of this finding, a series of 92 genomic DNA samples was screened from ethnically distinct patient groups with SLE to test the hypothesis that this mutation of C1q may be a widespread disease susceptibility gene. No further examples of this mutation were found.

Quantitative analyses of plasma opsonizing activity and polymorphonuclear cell response during phagocytosis: standardisation of a chemiluminescent method

Although measurement of chemiluminescence has become a widespread tool in the study of phagocytosis of peripheral neutrophils, several problems linked to spontaneous fluctuation in chemiluminescence and the number of variables involved have occasionally either limited its usefulness for clinical and experimental purposes or compelled operators to take particular care when using the technique. In the present paper, sources of variability are investigated and most of the parameters involved are thoroughly analysed and step-by-step normalised. A stochastic calibration procedure for validation of the method is applied and a monofunctional test protocol for quantitative evaluation of plasma opsonizing activity in whole blood chemiluminescence is suggested. With regard to the goal of proposing a reverse monofunctional test, we discuss the reasons why further studies aimed at standardised evaluation of the cellular components are needed.

A "complement-ary" AIDS vaccine

The human immunodeficiency virus uses the human complement system to its advantage. Is it possible to turn the tables with a vaccine?

Genetic susceptibility to severe course of nephropathia epidemica caused by Puumala hantavirus

Nephropathia epidemica (NE) caused by Puumala hantavirus is one type of hemorrhagic fever with renal syndrome (HFRS). There is considerable variability in the clinical severity of NE. Many infections are subclinical but the disease can even be fatal. We questioned whether the wide spectrum in the outcome of NE is dependent, on host-related immunological factors by determining the major histocompatibility complex markers (MHC) in 74 adult patients with NE. Patients with the most severe course of the disease had a very high frequency of HLA B8, C4A*Q0, and DRB1*0301 alleles. HLA B8 was found in all 7 (100%) patients with shock and in 9 of the 13 (69%) patients who required dialysis, versus in only 25 of 74 (34%) in the entire population, and in 14 of 93 (15%) controls. In addition, various other clinical findings pointing to a severe form of NE were found to be associated with these alleles. Interestingly, the same MHC alleles are risk factors for various autoimmune diseases. This is the first study where a certain HLA haplotype is found to be associated with the clinical course of an acute viral disease or acute nephritis.

Genetic deficiencies of complement

Genetic deficiencies of proteins of the complement system are associated with diverse clinical phenotypes. These clinical manifestations vary as a function of the specific component that is missing. Molecular and cellular biological methods, coupled with more intensive clinical studies, have defined the pathophysiological basis for this set of genetic disorders. Insights into the normal function of complement and its role in immunopathology have been derived from the extensive work in this field during the past few years.

Active Heymann nephritis in complement component C6 deficient rats

The mechanisms of renal injury that result in proteinuria in active Heymann nephritis (AHN) remain unclear, though data suggest that in analogy of the passive form of the disease the membrane attack complex C5b-9 may be involved. AHN was induced in an inbred strain of PVG/c-rats that are totally deficient in the C6 component of complement and are unable to form the lytic C5b-9 complex, as well as in non-complement deficient PVG/c+ rats that are immunologic identical to the deficient strain. In both groups of animals comparably high titers of anti-Fx1A autoantibodies were found after three weeks and persisted at 40 weeks. Proteinuria was also similar in both groups, and was first evident at six weeks. High levels of urinary protein, ranging from 200 mg/24 hr to 500 mg/24 hr, were found after 10 weeks and persisted up to one year. Renal biopsy findings at various times post-immunization were identical in both groups, including immunofluorescence staining for Ig and C3 deposits, and also EM findings of subepithelial electron-dense deposits were not different. The injection of heterologous rabbit complement, that partially and temporarily restored the CH50 activity in PVG/c- rats did not alter or hasten the disease. Long-term follow-up showed that all rats in both groups continued to have severe proteinuria and that most animals died between 8 to 12 months after disease induction, without renal impairment. EM findings in serial biopsies demonstrated that the growth of the subepithelial deposits as measured by surface area occurred between weeks 4 and 12. A positive correlation (r = 0.94) between the size of the deposits and the level of proteinuria was found. These studies demonstrate that the membrane attack complex of complement does not play a major role in AHN. The relationship of the size of the immune deposits to the level of proteinuria suggests that the growth of the immune deposits on itself initiate secondary mechanisms that damage the permselective characteristics of the glomerular membrane.

Physiology and pathophysiology of complement: progress and trends

The complement system comprises a family of at least 20 plasma and membrane proteins that interact in a tightly regulated cascade system to destroy invading bacteria and prevent the deposition of immune complexes in the tissues. This brief review addresses the basic mechanisms of complement activation and control and describes the active fragments produced during complement activation. The biological importance of the complement system is amply illustrated in patients with complement deficiencies, who are susceptible to bacterial infections and immune complex diseases. The involvement of complement in other immunological diseases is an expanding area of clinical research, supported by the development of new assays for the identification of complement activation. This area is discussed here with particular reference to neurological diseases. A promising new prospect involves the use of complement inhibitory molecules in therapy of complement-mediated disease and this exciting area is also discussed. Novel physiological roles of complement also are being revealed and new evidence that complement and complement receptors play an important role in reproduction is summarized. It is hoped that this brief overview will convey some of the enthusiasm currently pervading research in this underappreciated area of immunology.

In vitro cleavage of serum complement protein C3: a comparison between patients with adult periodontitis and periodontally healthy persons

This study tested the hypothesis that in vitro cleavage of C3 could be triggered with similar case in serum samples from patients with adult periodontitis (n = 26) as in samples from periodontally healthy subjects (n = 13). A lipoteichoic acid, a lipopolysaccharide and an aggregated IgG served as activators of complement. On the average, the periodontitis group generated significantly (p < 0.01) more C3d activation fragments than did the healthy group, as judged from rocket immunoelectrophoresis measurements. Cleavage of C4 and factor B were then assayed through immunoblotting, without prior purification of the sera. C4c fragments were seen in all activated samples, the healthy group causing significantly (p < 0.05) more C4 conversion than did the periodontitis group. Cleavage of factor B, taken as a measure of soluble amplification convertase formation, was about equal between the groups. We inferred therefore that the 2 groups produced comparable amounts of C3b. The results suggested, however, that periodontitis sera favour breakdown of the opsonin C3b, most likely by activating the regulatory proteins factor H and I. Lipoteichoic acid, causing moderate depletion of C4 and factor B, produced significantly (p < 0.01) more C3d fragments than the other two activators examined. It may be that complement activation is down-regulated in periodontitis sera, perhaps at the expense of adequate local opsonic function.

Reconstitution of the alternative pathway of complement by plasma infusions given to a patient with an SLE-like syndrome associated with a hereditary C3 dysfunction

OBJECTIVE

To reconstitute a dysfunctional form of complement factor C3 in a patient with a systemic lupus erythematosus (SLE)-like syndrome.

METHODS

The propositus was treated with plasma infusions during five sessions over a period of eight months.

RESULTS

The alternative pathway was reconstituted to normal levels for approximately two to three days after each infusion. C3 fragments were incorporated into previously detected deposits of IgG and IgM at the dermal-epidermal junction and the immune complex levels gradually decreased during the whole treatment period.

CONCLUSION

The reconstitution appears to result in the solubilisation of tissue immune complexes and a subsequent transportation to the fixed macrophage system.

Hereditary C6 deficiency in a strain of PVG/c rats

A chance observation has led to the discovery of a strain of PVG rats (PVG/c-) which are deficient in complement (C) component C6. Analysis of total haemolytic activity (CH50) of PVG/c- serum revealed an absent CH50 activity compared with serum of other rat strains and of a PVG/c rat (PVG/c+) that showed normal C activity. Thus, the PVG/c- rat was unable to activate the C5b-9 membrane attack complex. To gain insight into the complement abnormalities, analysis of individual C components was performed. Testing the PVG/c- serum in a C6 haemolytic assay and using deficient human sera showed a deficiency of C6 in the PVG/c- rat. Highly purified human C6 and human sera deficient in other components were able to reconstitute the CH50 activity of the PVG/c- rat. The possibility that an inactivator of C was present in PVG/c- serum was excluded. The deficiency was found to be inheritable and under the control of an autosomal recessive gene. Furthermore, tissue antigens and immunity of the PVG/c- rat were found to be identical to those determined in the PVG/c+ rat. With regard to their health status, the PVG/c- animals seem to have no disadvantages compared with PVG/c+ rats when held under the same conditions within the protected environment of animal facilities. Taken together, both rat strains provide an unique animal model for studying the biological role of C, particularly the C5b-9 membrane attack complex in experimental medicine.

An indirect effect of an antibody on complement deposition and lysis of differently sensitized surrounding cells

Lysis of papain-treated group A and B erythrocytes by human complement was studied by an anti-A (BRIC. 131) and an anti-B (BRIC. 30) IgM monoclonal antibody in 51Cr release assays. The indirect effect of membrane-bound antibody, i.e. its influence on complement binding to sensitized surrounding cells, was examined in a cold target competition test in which sensitized, non-labelled cells are present along with sensitized labelled cells and complement. The mode by which anti-A antibodies indirectly suppressed lysis of sensitized B cells up to 20-fold was studied by following C1q and C3b binding. C1q binding to both types of erythrocytes was not altered in mixed populations of erythrocytes in the presence of both antibodies. Binding of C3b to a mixture of both cell types was, however, suppressed, when both antibodies were present. C3b deposition in mixed cell populations did not reach a significantly higher extent than deposited to one type of erythrocyte alone. This was consistent with the results from competitive lysis and suggests that the anti-A captured most C3b at high anti-A concentrations and deprived the similarly sensitized B erythrocytes of complement. We think that this phenomenon is not due to an uneven removal of complement regulatory proteins from A and B erythrocytes by papain. Instead, the phenomenon might be due to an inherent property of anti-A mAb to better produce nucleation sites for C3 convertases which, upon binding factor B, better compete for the limiting factor D. A mathematical analysis of cold target competition experiment (containing 2430 individual measurements) also shows that the distribution of complement between the competing A and B erythrocyte population is uneven, since it predicts that in any given antibody combination the majority of complement is bound to A erythrocytes. This is consistent with the measured average percentage of lysis.

Inherited complement C3 deficiency: a defect in C3 secretion

The molecular basis of inherited complement C3 deficiency in a 20-year-old newly diagnosed male patient was studied. Using an enzyme-linked immunosorbent assay, the patient's C3 serum level was found to be approximately 7 micrograms/ml, which is less than 1% of normal. In contrast, Northern analysis indicated that the patient's C3 mRNA was of normal size and quantity. Peripheral blood monocytes (PBM) and skin fibroblast cultures (F) from the patient and from healthy donors were labeled for 2 h with [35S] methionine. Analysis of cell lysates and supernatants by immunoprecipitation and sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) demonstrated normal levels of C3 in lysates of patient's PBM and F. However, C3 secretion in the patient's cells was extremely reduced, with pulse-chase experiments demonstrating a long delay in the disappearance of intracellular C3. Secretion of C1r and factor B by the patient's cells was normal. Lipopolysaccharide and interleukin-1 increased C3 synthesis in the patient's PBM and F, but had no effect on the secretion. SDS-PAGE analysis of trypsin-cleaved intracellular C3 revealed an aberrant cleavage profile for the patient's C3. Collectively, these data indicate that C3 deficiency in this patient is due to a defect in the C3 secretion, probably as the result of abnormality in the proC3 structure.

Immune function of patients receiving recombinant human interleukin-6 (IL-6) in a phase I clinical study: induction of C-reactive protein and IgE and inhibition of natural killer and lymphokine-activated killer cell activity

Interleukin-6 (IL-6) is a cytokine that acts on a variety of cell types, including myeloid progenitor cells and B and T lymphocytes. It has been found to activate cytotoxic T cells and natural killer (NK) cells and to induce T-cell-mediated antitumour effects in animal models. In a phase I clinical trial of recombinant human IL-6, 20 patients with advanced cancer were entered to receive daily subcutaneous injections of IL-6 over 7 days followed by a 2-week observation period and another 4 weeks of daily IL-6 injections. Doses varied between 0.5 microgram/kg and 20 micrograms/kg body weight and immune functions were monitored throughout. At all dose levels IL-6 administration led to a marked increase in serum levels of C-reactive protein and a moderate rise in complement factor C3. The proportions of CD4, CD8 or HLA-DR lymphocytes in peripheral blood did not alter with IL-6 treatment nor did the in vitro proliferation of peripheral blood mononuclear cells induced by either phytohaemagglutinin, pokeweed mitogen or fixed Staphylococcus aureus. By contrast, NK cell activity, lymphokine-activated killer (LAK) cell activity and proliferation induced by in vitro culture with interleukin-2 (IL-2) were suppressed at doses exceeding 2.5 micrograms/kg. Serum IgE levels were consistently elevated over the IL-6 dose range but IgM, IgG and IgA levels were unaffected. In summary there is a dose-dependent induction of acute-phase proteins by in vivo IL-6 treatment. At higher IL-6 doses there is a suppressive effect on NK and LAK activity measured in vitro. IL-6 may thus be useful in combination cytokine therapies that seek to suppress LAK and favour cytotoxic T lymphocyte responses. The rise in IgE levels in response to IL-6 was unexpected and suggests a more pivotal role than previously known for the control of IgE production; this could include IgE-related diseases.

A genetic association between systemic lupus erythematosus and tumor necrosis factor alpha

We have investigated the significance of tumor necrosis factor alpha (TNF-alpha) polymorphism in relation to systemic lupus erythematosus (SLE) and autoantibody production. Typing of HLA-B, -DR and TNF was performed in 81 Caucasian SLE patients and 168 Caucasian controls. The presence of anti-Ro and anti-La antibodies was also determined in patients. The frequency of the TNF2 allele increased in SLE compared with controls [0.24 vs. 0.17, p = 0.04, odds ratio (OR) = 1.6], as did HLA-DR3 (0.25 vs. 0.13, p < 0.01, OR = 2.3) and HLA-B8 (0.23 vs. 0.15, p = 0.02, OR = 2). Although HLA-DR3 showed the strongest disease association, we could not demonstrate association of HLA-DR3 or TNF2 with SLE independently of each other. Within SLE a much stronger association of TNF2 was seen with autoantibody production: anti-Ro antibody (0.39 vs. 0.16, p < 0.001, OR = 3.4) and anti-La antibody (0.43 vs. 0.19, p < 0.001, OR = 3.2). When analyzed independently of each other, however, HLA-DR3 remained significantly associated with autoantibodies, while TNF2 did not. These data suggest that on the B8-DR3 haplotype, TNF-alpha polymorphism may play a role in SLE susceptibility, but it is not primarily associated with autoantibody production.

Complete functional C1q deficiency associated with systemic lupus erythematosus (SLE)

A complete functional deficiency of C1q is described in a patient suffering from SLE. From reduced plasma C1 activity of the parents a hereditary trait was assumed. The defective C1q molecule was haemolytically inactive, did not bind to immune complexes, and was not recognized by the monocyte C1q receptor. C1 activity in the patient's serum could be restored by the addition of purified C1q. Analysis by gel-filtration and ultracentrifugation experiments revealed an immunoreactive molecule of about 150 kD mol. wt, corresponding to one structural subunit of the C1q macromolecule, containing two A chain-B chain dimers and a C-C chain dimer. Applying Southern blot analysis with cDNA clones encoding for the three individual chains of the C1q molecule, no restriction fragment length polymorphism was detected, ruling out possible major alterations of the genetic information.

Complement and glomerulonephritis--an update

The complement (C) system in man and its relationship to disease has been the subject of intensive research. In this review, we update the information concerning the nature of the various C components, and present some of the similarities between structure and function of the C components and their respective genes. The clinical problems which are encountered in individuals with acquired C abnormalities and with a genetically determined deficiency of a single component provide helpful clues to understanding the affected patients and the possible functional importance of the particular deficient component. The steady progress in identifying both normal variants of C components and the gene defects which produce C deficiencies offers the prospect of correlating structure of the C components with possible pathogenic roles in disease. Genetically determined C abnormalities are more commonly recognized during childhood. An appreciation of the basic aspects of the C system is a helpful tool for the pediatric nephrologist.

HLA antigens and complement C4 allotypes in patients with chronic biologically false positive (CBFP) seroreactions for syphilis: a follow-up study of SLE patients and CBFP reactors

We report a follow-up of our previous study of HLA markers in 118 unrelated patients: 49 with definite systemic lupus erythematosus (SLE) (group 1), 32 with definite or probable SLE and chronic biologically false positive (CBFP) seroreactions for syphilis (group 2), and 37 CBFP reactors (group 3). Definite SLE was confirmed in 28 (90.3%) of the patients in group 2, equally in HLA B8- and HLA B7-positive patients. Three of the CBFP reactors developed SLE, two (40%) out of five HLA B8-positive as compared to one (6.6%) out of 15 HLA B7-positive CBFP reactors (P = 0.07). Fourteen patients died (groups 1 and 2). Eight of the 24 HLA B8-positive patients died in contrast to one of the 20 HLA B7-positive patients (P < 0.02). Of the CBFP reactors, 70.9% had complement C4 null alleles as compared to 47.9% in controls (P = 0.05) and 50% had C4A null alleles as compared to 17.8% in controls (P < 0.05). C4B null alleles were found in 28.6% (28.6% in controls, P is not significant). The null alleles for C4A were not solely in a linkage disequilibrium with the HLA B8 DR3 haplotype. CBFP reactors with C4A null alleles had a higher risk of developing SLE, lupus-like disease or symptoms such as photosensitivity, cutaneous vasculitis and/or autoantibodies than did those with no C4A null alleles (P < 0.02).

Complement defense mechanisms

The susceptibility of complement-deficient individuals to various severe infections, and studies of the effector mechanisms involved in the destruction of infectious agents, demonstrate the importance of complement in providing an effective host defense system. It is also becoming increasingly apparent that complement not only plays a role in 'natural' defenses against infection and in enhancing the antibody-mediated effector mechanisms, but also influences adaptive immune responses directly.

Complement component C4 deficiencies and gene alterations in patients with systemic lupus erythematosus

Deficiency of complement component C4 is considered playing a role in the genetic predisposition for systemic lupus erythematosus (SLE). The purpose of this study was to characterize the genomic alterations of the C4 and CYP21 genes in 40 caucasoid patients with SLE by C4 allotyping and by RFLP analysis. Nineteen patients (47.5%) carried C4A null alleles and eight patients (20.0%) C4B null alleles. SLE patients had more frequent C4A null alleles (47.5%) than healthy individuals (20%) (chi 2 = 10.75; P < 0.005). The commonest molecular alteration in the patients with C4A null alleles was a large gene deletion affecting both C4A and CYP21A genes. However, among the patients with C4A null alleles, 16.7% persons had no detectable C4A deletion. The non-expression of C4A gene might be due to defects at various levels of gene expression (i.e. transcription and translation). Among the patients with C4B null alleles, 62.5% persons had no detectable gene lesion, whereas 37.5% showed a C4B deletion including both C4B/CYP21A or C4B/CYP21B genes. Duplication of the C4B gene was not rare in SLE patients, as we found 15.0% of the patients with a heterozygous C4B/CY21A gene duplication. The patients typed as having C4B gene homoduplication (B1,1) demonstrated two long C4B loci, whereas heteroduplication (B1,2) displayed two short loci, therefore the type of C4B gene duplication may be related to the gene length. In conclusion, C4 deficiencies observed in 26 of the 40 SLE patients studied were very heterogeneous. In every case, the gene alteration affected both C4 and CYP21 genes.

Complement and lupus: old concepts and new directions

In this review it is our intention to outline briefly the relevance of the complement system in systemic lupus erythematosus. Three main issues will be addressed: the role of complement in handling immune complexes (ICs), the association between complement deficiencies and IC diseases, and the value of measuring complement components and their conversion products in monitoring disease activity.

Antibodies to retroviral proteins in autoimmune connective tissue disease. Relation to clinical manifestations and ribonucleoprotein autoantibodies

OBJECTIVE

To study the relationship between antibodies that recognize human retroviral proteins and the presence of clinical features and ribonucleoprotein antibodies in patients with autoimmune connective tissue diseases (CTDs).

METHODS

Antibodies against native human immunodeficiency virus type 1 (HIV-1) and human T cell leukemia/lymphoma virus type I, recombinant HIV-1 Nef protein, and ribonucleoprotein antigens were determined by immunoblot of sera from 65 prospectively studied patients with definite or suspected CTDs of autoimmune type.

RESULTS

Antibodies to retroviral proteins (ARP), most frequently to HIV Gag proteins p55 and p24, were found in 64% of 22 patients with systemic lupus erythematosus (SLE), in 63% of 8 patients with discoid LE (DLE), in 75% of 8 patients with mixed connective tissue disease (MCTD), and in 26% of 19 individuals with chronic biologically false-positive (CBFP) seroreactions, but not in 8 patients with subacute cutaneous lupus erythematosus. No clear correlation of ARP with antibodies to any specific small nuclear RNP antigen was observed. The most striking finding was that recurrent infections, both in LE patients and in those with CBFP reactions and widespread, acral discoid skin lesions, occurred significantly more often in ARP-positive patients.

CONCLUSION

The occurrence of antibodies reacting with human retroviral proteins is associated with severe skin lesions and recurrent infections in SLE, DLE, and MCTD patients, and with a disposition toward developing systemic disease in CBFP reactors.

Gene frequency and partial protein characterization of an allelic variant of mannan binding protein associated with low serum concentrations

Low plasma concentration of mannan binding protein (MBP) has been shown to be the basis for a common opsonic deficiency and suggested to be caused by a single nucleotide substitution at base 230 of exon 1 in the MBP gene. This substitution causes a replacement of glycine (codon GGC) with aspartic acid (codon GAC). Of 123 healthy Danish individuals investigated by polymerase chain reaction performed on exon 1, followed by restriction fragment length polymorphism or allospecific probing, 93 were homozygous (75.6%) for GGC, 28 heterozygous (22.8%), and two homozygous for GAC (1.6%). The gene frequency of the GAC allele was found to be 0.13. DNA sequencing of the cloned exon 1 from one GAC homozygous individual revealed no other substitution. The median MBP concentration in the group containing the GAC allele was 6.4 times lower than in the GGC homozygous group (195 and 1234 micrograms/l respectively). However, the range in plasma concentrations of MBP was wide and overlapping between the groups. MBP protein was detected in both the GAC homozygotes (9 and 387 micrograms/l). Furthermore, no difference in relative mass and biological activity (mannan binding) was found when sera containing the two forms of MBP were investigated. Accordingly, it can be concluded that the GAC allele is able to produce a functional MBP protein which may be detected in serum at low concentrations.

Complement receptor 1 (CR1) expression in chronic myeloid leukemia

The complement receptor 1 (CR1), also called CD35, is a polymorphic glycoprotein which mediates a variety of neutrophil functions, including phagocytosis and, probably, tumor cell cytotoxicity. The role played by this molecule in chronic myeloid leukemia (CML) is not yet well understood. CML frequently shows a marked decrease of CR1 antigens on both the neutrophil population and myeloid precursors. This reduced expression appears to be related to disease activity, since patients at more advanced clinical stages, as well as those who develop blastic crisis, have been found to express the lowest levels of CR1 antigens. At the onset of the disease low CR1 expression on CML neutrophils seems to be associated with a higher risk of blastic transformation. Furthermore, CML neutrophils deficient in CR1 lack the ability to respond to PMA stimulation, suggesting a failure in CR1 granular storage. In patients lacking CR1, the number of receptors increased to normal levels following exposure of CML cells to therapeutic concentrations of recombinant alpha interferon. The role played by the CR1 molecule in sustaining neutrophil-mediated tumor cell cytotoxicity has yet to be definitively proved; studies performed by our group are relevant here, since complete suppression of tumor lysis following receptor neutralization by anti CR1 monoclonal antibodies was demonstrated in a large number of normal and CML individuals. In CML patients, the evidence of a direct relationship between lytic activity and antigen receptor levels seems to further support the involvement of CR1 molecules in tumor cell lysis, function.(ABSTRACT TRUNCATED AT 250 WORDS)

Morbidity study of extruder personnel with potential exposure to brominated dioxins and furans. I. Results of blood monitoring and immunological tests

The potential for exposure of employees to polybrominated dibenzofurans (PBDFs) and dibenzo-p-dioxins (PBDDs) during extrusion blending of resins containing decabromodiphenyl ether was established through previous air monitoring (area samples) and biomonitoring studies. The findings presented herein are further biomonitoring results for 42 employees and immunological tests for exposed and referent employees. Among potentially exposed men, 2,3,7,8-TBDF and 2,3,7,8-TBDD concentrations in blood lipid ranged from non-detectable to 112 parts per trillion (ppt) and from non-detectable to 478 ppt respectively. Biomonitoring results correlated well with assignments in the extruder work area when adjusted for process changes and engineering improvements and provided biological half life estimates of between 1.1 and 1.9 years for 2,3,7,8-TBDF and between 2.9 and 10.8 years for 2,3,7,8-TBDD. Results for 16 measures of the immune system were examined in relation to exposure (exposed v referent group) and in relation to the biomonitoring data. Some individual trends in immunological parameters with exposure and covariates such as age and cigarette smoking were found (for example, an increase in complement C4 with increasing concentrations of PBDFs and PBDDs, increased lymphocyte subpopulation counts with cigarette smoking); however, the overall clinical assessment was that the immune system of exposed employees was not adversely impacted at these burdens of PBDFs and PBDDs.

Macrophage-bound C3 fragments as adhesion molecules modulate presentation of exogenous antigens

The involvement of complement in the response to T cell dependent antigens is generally accepted, however the mechanism has not been clarified. We compared the T cell response in vitro, using antigen-pulsed macrophages from normal and genetically C3-deficient guinea pigs, and show, that C3-fragments fixed covalently to the surface of the antigen-presenting cells are involved in the triggering of responder T cells. Binding of guinea pig C3-specific mAb to oil-elicited, OVA- and PPD-pulsed macrophages of C3D guinea pigs is reduced compared to normal cells, while the expression of Ia antigens is the same. C3-like peptides can be immunoprecipitated only from the lysate of oil-elicited normal cells. These C3-fragments are fixed to the cell-membrane via ester-bonds, since they are released upon treatment with hydroxylamine. In comparison with normal cells, the antigen-presenting capacity of macrophages derived from C3D animals is strongly impaired in cultures containing 10% normal guinea pig serum. A further impairment is observed in cultures with 10% C3D guinea pig serum. Two of the tested C3-specific mAb inhibited antigen-induced T cell proliferation in a dose-dependent manner. Our data point to the importance of C3, as a bivalent molecule, having the capacity to facilitate the cooperation between the antigen-presenting cell and the responder T lymphocytes.