SEARCH · PubMed Health
Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.
Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.
The effects of a 2.5-h running test on the concentrations of the complement cleavage products C3a, C4a and C5a in plasma were examined in eight healthy young males. In all participants the C3a and C4a values were raised during (1 h after the start) and immediately after exercise. C4a was also raised 1 and 3 h after the race. These results provide evidence for complement activation after prolonged exercise.
PURPOSE AND PATIENTS AND METHODS: Both complement and contact system of coagulation have been implicated in the pathophysiology of sepsis. We therefore measured levels of the complement activation products C1-C1-inhibitor complexes and C3a in serial plasma samples (obtained every six hours) from 48 patients with clinically suspected sepsis, and related these levels to the clinical outcome. C4a was also measured in samples obtained on admission. RESULTS: C3a levels were elevated in 47 patients at least once during the observation period. These levels appeared to be considerably higher in patients who died than in patients who survived. This difference was found for the levels on admission (p = 0.0003), as well as for the highest (p = 0.0010) and the lowest (p less than 0.0001) levels encountered in each patient. The mortality in patients with plasma C3a levels of 13 nmol/liter or less on admission (27 patients) was 33 percent, compared with 86 percent in patients with levels of 14 nmol/liter or more. Patients with septic shock had significantly higher C3a levels than normotensive patients (p values between 0.046 and 0.004). No significant differences in C3a were found between patients who had respiratory distress syndrome and those who did not. C4a levels in plasma samples obtained on admission were elevated in 43 patients. These levels correlated very significantly with C3a levels (p less than 0.0001), and showed similar associations with a fatal outcome. C1-C1-inhibitor complexes were elevated in 23 patients at least once during the observation period. These patients had significantly higher levels of C4a and C3a than patients with normal amounts of C1-C1-inhibitor complexes. Patients who died had higher levels of C1-C1-inhibitor complexes than patients who survived. However, this difference was not significant. CONCLUSION: On the basis of our results, we propose that activation of the complement system via the classical pathway is involved in the development of fatal complications in sepsis.
There is a striking difference in the leukocyte infiltration pattern between synovial tissue and fluid of rheumatoid arthritis, a monocyte/macrophage-predominant infiltration in the former and a polymorphonuclear leukocyte (PMN)-predominant one in the latter. In extracts of rheumatoid arthritis synovial tissue, there is a strong chemotactic activity to monocytes but a negligible one to PMNs. The monocyte-specific chemotactic factor in the extracts represents dimers (and oligomers) of the S19 ribosomal protein which are cross-linked by a transglutaminase-catalyzed reaction. This oligomer formation may correlate to apoptosis in the lesion. On the other hand, in the synovial fluids there is the co-presence of chemotactic factors effective on PMNs as well as on monocytes and a strong chemotaxis inhibitor specific to monocytes. This inhibitory molecule is C4a which is liberated from complement component 4 in the presence of immune complexes. C4a exhibits its inhibitory activity indirectly by stimulating monocytes to release an autocrine or paracrine inhibitory cytokine to monocyte chemotaxis. These molecular mechanisms seem at least partly to cause the two distinct patterns of leukocyte infiltration in rheumatoid arthritis.
Previous studies have suggested that activation of the complement system might be a major mechanism for posttransfusion non-immunoglobulin (Ig) E-mediated anaphylactic reactions, but its causative effect has not been clearly demonstrated in human models. Serial plasma samples were collected from a patient with severe von Willebrand disease, IgG alloantibodies against von Willebrand factor (vWF), and a history of posttransfusion anaphylaxis. During an 18-day period the patient was treated with factor VIII-vWF concentrate and with recombinant factor VIII. Complement system activation was assessed from plasma levels of C4a, C3a, cleavage products of complement factor B, soluble terminal complement complex, C1 inhibitor and C4-binding protein, and the contact phase of coagulation was assessed from plasma levels of activated factor XII and cleaved high-molecular-weight kininogen. Plasma levels of antibodies to vWF and complement-fixing IgG-vWF complexes were also evaluated. Symptoms of anaphylaxis and signs of complement activation were present only when IgG antibodies to vWF were measurable during replacement with factor VIII-vWF concentrate (days 1 and 6). IgE, IgA, and IgM antibodies to vWF were not detectable in plasma at any time. Replacement with recombinant factor VIII (days 7 to 18) secured hemostasis and did not elicit anaphylactic reactions, and complement parameters did not significantly change even when antibodies to vWF reached peak plasma levels. This prospective study of a natural clinical model indicates a cause-effect relationship between formation of IgG-vWF complexes and massive complement activation in posttransfusion non-IgE-mediated anaphylactic reactions.(ABSTRACT TRUNCATED AT 250 WORDS)
Associations between C4 deficiency and autoimmune disorders have been found over the past several years. Since autism has several autoimmune features, the frequencies of null (no protein produced) alleles at the C4A and C4B loci were studied in 19 subjects with autism and their family members. The autistic subjects and their mothers had significantly increased phenotypic frequencies of the C4B null allele (58% in both the autistic subjects and mothers, compared with 27% in control subjects). The siblings of the autistic subjects also had an increased frequency of the C4B null allele, but this increase was not significant. The fathers had normal frequencies of this null allele. All family members had normal frequencies of the C4A null allele, all normal C4A and C4B alleles and all BF and C2 alleles.
An animal model has been used to address the question of the biological importance of the known structural difference between the two isotypes of human C4, i.e., C4A and C4B. Guinea pigs deficient in C4 were reconstituted transiently with either human C4A or C4B protein and immunized with the bacteriophage phi X174. Results from this study showed that C4A-reconstituted animals made a secondary response, i.e., switch from IgM to IgG; whereas the C4B-reconstituted animals did not.
The two forms of human C4 were compared in their haemolytic activity and in their capacity to mediate inhibition of immune complex precipitation in human C4 deficient sera. Whereas haemolysis by C4B was 3.2 fold more efficient than by C4A, C4A was 1.7 fold more efficient at inhibiting immune precipitation than C4B. Thus the biological properties of the two forms of human C4 are different and it is suggested that C4A is mainly involved in immune complex clearance reactions.
Thiol compounds have been investigated as inhibitors of the covalent binding reaction of human complement protein C4 using Sepharose-C1s as a combined activating and binding surface. o- and p-substituted aminothiophenols are equally effective inhibitors, whereas the m-substituted compound is a less potent inhibitor. The anti-hypertensive drug captopril is also shown to inhibit the covalent binding reaction. A comparison of the effects of these compounds on the covalent binding reaction of isolated C4A and C4B has been made. Results suggest that a Pro-to-Leu substitution in C4B is likely to account for the differences in inhibitory potency of C4B compared with C4A observed with the aromatic inhibitors.
Complement activation by the alternate pathway has been implicated in the pathophysiology of cardiopulmonary bypass (CPB), and laboratory studies suggest that the complement cascade may be activated by the protamine-heparin complex. To determine if the administration of protamine to patients receiving heparin activates complement, we studied 100 patients undergoing CPB by assaying levels of C3a and C4a (classic pathway) at regular intervals before and after protamine administration. In group I (90 patients), protamine was given at the usual interval (median 5 minutes) after CPB. In group II (10 patients), protamine was withheld until skin closure (median 45 minutes) after CPB. Results demonstrated that C4a was not activated during CPB in either group. After CPB, the C4a level in group I was 459 ng/dl and increased to 1047 ng/dl 10 minutes after protamine administration (p less than 0.001). In group II, the C4a level was 484 ng/dl at the end of CPB and 354 ng/dl 15 minutes later, which corresponds to the value immediately after protamine administration in group I. The delayed administration of protamine in group II caused a significant increase in C4a at the time of skin closure (1090 ng/dl; p less than 0.001). Corresponding results from C3a analysis before and after protamine administration confirmed the activation of complement cascade. Our study provides the first clinical evidence that the protamine-heparin complex activates complement via the classic (C4a) pathway. The hemodynamic effects of protamine after CPB may be related to complement activation.
In general, C4A allotypes of human C4 show one-fourth to one-third the hemolytic activity of C4B allotypes. An exception to this rule is C4A6 which is almost totally deficient in hemolytic activity. Previous studies have localized the defect in C4A6 to the C5 convertase stage. Of the two critical events required for C5 cleavage, namely formation of a covalent adduct between C3b and the C4b subunit of the C3 convertase (C4b2a), and binding of C5 to this C4b-C3b complex, it is a defect in the latter step that accounts for the aberrant activity of C4A6. DNA sequencing studies described in a companion paper have suggested that the sole C4A6-specific difference was a Trp for Arg replacement at beta-chain residue 458. To directly ascertain whether this single substitution was responsible for the hemolytic defect in C4A6, we have used site-directed mutagenesis to introduce this change into both C4A and C4B cDNA expression plasmids. We found that the R to W replacement totally abrogated hemolytic activity. However, irrespective of the amino acid at residue 458, the mutant proteins behaved like their wild-type counterparts with respect to covalent binding to C1-bearing targets, i.e., the C4B recombinants displayed higher binding to sheep and human red cells than did the C4A counterparts. Furthermore, the mutants were able to form covalent C4b-C3b adducts. There was, however, substantially less C5 cleavage produced by cell-bound C4boxy23b complexes made with R458W mutant C4B than with wild-type C4B. These results are consistent with the sole defect in the mutants being at the C5 binding stage and strongly suggest that Arg 458 of the C4 beta-chain contributes to the C5 binding site of the molecule.
BACKGROUND: Poly-2-methoxyethylacrylate (PMEA) is a new coating material, and several studies have revealed that PMEA-coated cardiopulmonary bypass (CPB) circuits have good biocompatibility. This study sought to compare this biocompatibility with those of heparin-coated and noncoated circuits. METHODS: Forty-five patients undergoing coronary artery bypass grafting were randomly assigned to PMEA-coated (group P, n = 15), heparin-coated (group H, n = 15), or noncoated (group N, n = 15) circuit groups. Clinical data and the following markers were analyzed: (1) platelet preservation by number of platelets; (2) complement (C) activation by C3a and C4a levels; (3) inflammatory response by interleukin-6 (IL-6) and interleukin-8 (IL-8) levels. RESULTS: Platelet numbers were significantly preserved in group P compared with groups N and H. Postoperative blood loss did not differ among the groups. During CPB, C3a values were significantly lower in group H (536 +/- 145 ng/mL) than in group P (1,458 +/- 433 ng/mL, p < 0.01) and group N (1,815 +/- 845 ng/mL, p < 0.01). The C4a values did not differ 60 minutes after CPB initiation among the groups. The IL-6 and IL-8 levels were significantly lower in group P and group H than in group N. CONCLUSIONS: The PMEA coating was superior to heparin coating and noncoating in preserving platelets, and was equivalent to heparin coating in terms of the perioperative clinical course and inhibition of inflammatory cytokines, but slightly inferior in reducing complement activation.
The distribution of C4 phenotypes and gene frequencies were studied in 104 genetically unrelated persons of Slovakia using high-voltage agarose gel electrophoresis with subsequent immunofixation. Five C4A alleles and three C4B alleles were detected. The gene frequencies were as follows: A2 = 0.0576, A3 = 0.7644, A4 = 0.0336, A6 = 0.0625, AQ0 = 0.817, B1 = 0.7836, B2 = 0.1009, BQ0 = 0.1153. The C4AQ0 and C4BQ0 alleles established by densitometry appeared in the Slovak population in 16.34% and 23.07%, respectively.
The complement system is an important humoral defense mechanism that plays a relevant role against microbial agents, inflammatory response control, and immunocomplex clearance. Classical complement pathway activation is antibody-dependent. The C4 component participates in the initial step of activation, and C4 expression is determined by 2 pairs of allotypes: C4A and C4B. Deficiencies in C4 allotypes have been associated with several diseases. The aim of the present review is evaluate the reported data in the literature regarding specific C4A and C4B deficiencies and characterize their clinical relevance. We searched the MEDLINE and LILACS databases. Papers referring to total C4 deficiency without allotype evaluation and case reports of primary C4 deficiency were not included. Deficiencies in C4 allotypes have been associated with Mycobacterium leprae infection, erythema nodosum, systemic sclerosis with anti-topoisomerase I antibodies, intermediate congenital adrenal hyperplasia with DR5 genotype, diabetes mellitus type 1 with DR3,4 genotype, and diabetes mellitus with antibodies against islet cells. C4 allotype deficiency is also related to C4B deficiency and autoimmune-associated diseases, such as systemic lupus erythematosus, or diseases with an autoimmune component, such as autism. Some reports associate C4A with thyroiditis after delivery as well as limited and systemic sclerosis without anti-topoisomerase I antibodies. However, the studies with C4A and C4B have been concentrated in isolated populations, and some of the studies could not be reproduced by other authors.
Increased prevalence of C4 null alleles is a common feature of autoimmune diseases. We have shown previously that complement-dependent prevention of immune precipitation (PIP) is defective in patients with systemic lupus erythematosus (SLE), and correlated this defect with C4A*Q0 and low levels of the C4A isotype. To further clarify the role of C4A in the aetiology of SLE, we now extend our studies to other diseases which have been associated with C4A*Q0. The frequency of C4A*Q0 was increased in Icelandic patients with coeliac disease (0.50; P < 0.001), Grave's disease (0.30; P = 0.002) and insulin-dependent diabetes mellitus (0.23; P = 0.04) and in British patients with dermatitis herpetiformis (0.42; P = 0.002) and this was reflected in low levels of C4A. In spite of this, PIP was normal in these patients, and in marked contrast to our previous observations on connective tissue diseases, PIP measurements in these patient groups correlated more strongly with levels of C4B (r = 0.51, P = 0.0000004) than C4A. Patients with increased levels of anti-C1q antibodies had significantly lower PIP than patients without such antibodies (P < 0.01) and a negative association of PIP with anti-C1q antibodies was also reflected in an increased prevalence (P = 0.006) and levels (P = 0.006) of anti-C1q antibodies in patients with subnormal PIP, as well as a negative correlation between PIP and anti-C1q antibodies (r = - 0.25, P = 0.02). These results show that the PIP defect cannot be explained by low levels of C4A alone and suggest that measurements of anti-C1q antibodies may be useful in future studies on the molecular cause of the PIP defect in autoimmune connective tissue disease.
Complement component C4 is encoded by two nearly identical genes, C4A and C4B, that encode a C4 precursor that is proteolytically cleaved into the alpha, beta and gamma subunits of the mature protein. C4 is expressed primarily in liver and to a much lesser extent in immune cells. We have identified a unique 1 kb RNA transcript, termed Z, that arises from a cryptic promoter lying in the intron between exons 35 and 36 of the C4 gene. Primer extension, RNase protection, and 5' RACE experiments locate the cap site in intron 35, 55 bases upstream from exon 36. Northern blotting and RNase protection assays show that expression of this 1 kb Z RNA transcript is confined to the adrenal gland. Z RNA contains the same open reading frame as C4 which predicts a protein of 131 amino acids, but antisera to C4 do not interact with epitopes on this protein when it is synthesized by cell-free translation, hence the presence or absence of a Z protein in vivo could not be determined. Transfection of Z promoter/reporter constructs into human adrenal NCI-H295 cells shows that most if not all of the sequences required for high-level adrenal expression lie within 235 bases upstream from the cap site, but that this region is inactive when transfected into COS-1, JEG-3 and Hep-G2 cells, suggesting it contains an adrenal-specific element. The 222 bases upstream from the cap site are 75% identical in the human C4A and mouse Slp genes, and contain a potential binding site for steroidogenic factor 1 (SF-1), an orphan zinc-finger nuclear receptor. We propose that this region, like a nearby region in the mouse genome, functions as an upstream element of the P450c21 promoter, and may be a component of an adrenal-specific locus-control region.
The analysis of genetic polymorphism in C4 was performed on EDTA-plasma from 169 healthy unrelated Koreans. Plasma samples were subjected to high-voltage agarose gel electrophoresis followed by immunofixation. C4B allotypes were further detected by a hemolytic overlay method. The allele frequencies of C4A and C4B were as follows; for C4A, C4A*3 = 0.6099, C4A*4 = 0.1702, C4A*Q0 = 0.1525, C4A*2 = 0.0461, and C4A*R = 0.0213; for C4B, C4B*1 = 0.6406, C4B*2 = 0.2740, C4B*5 = 0.0569, C4B*Q0 = 0.0178, and C4B*R = 0.0107. C4A*3 and C4B*1 were among the most common alleles at each locus. C4A*6 was not detected in this study, but this allele is relatively common in both Caucasoid and Negroid populations. C4B*5 is a common allele in Asian, which is rare in Caucasoids and Negroids. C4B*5 appeared to be a characteristic allele of Oriental. In the C4A locus, five individuals with duplicated allotypes (three C4A 3,3 + 2, one C4A 4,3 + 2, and one C4A 3,3 + 3) were observed, and in the C4B locus, one individual with duplicated allotype (C4B 1,1 + 1) was detected.
A series of diabetic patients from 3 centres in South India have been tested for HLA A, HLA B, BF, C2, C4A, C4B and GLO types. For insulin-dependent diabetes mellitus (IDDM) patients there was a significant increase in HLA B8, of BF F and decrease of C4 A6. No significant variation in HLA, BF, C2 or GLO frequencies was found in non-insulin-dependent diabetes mellitus (NIDDM) patients, but there was a significant decrease in C4B 1 and an increase in C4B 2. The HLA and BF association in South Indian IDDM patients is very different from that reported previously in North India.
The objective was to re-evaluate the association between class II HLA-DR and DQ MIIC antigens and postpartum thyroiditis (PPT) and to determine the prevalence of the class III complement allotypes of Properdin factor B (Bf), C4A and C4B in this condition. Two hundred and sixty-five (of 2897) pregnant women screened positive for thyroid autoantibody activity took part. Further blood samples were obtained for HLA class II (185) and complement (193) typing. The severity of the ensuing PPT was assessed by measuring thyroid function during the postpartum year. The HLA-DR and DQ phenotypes were assigned from restriction fragment length polymorphism analysis, and Bf, C4A and C4B allotypes were determined by immunofixation with anti-Bf or anti-C4 antibodies after electrophoresis. A weak association between the HLA class II antigens and PPT, as indicated by a reduced frequency of DR15 and DQ6 together with an increased frequency of-DR5 and DQ7, was confirmed. However, only the change in DR5 frequency remained significant after correction (corrected p < 0.05). Postpartum thyroiditis was also associated with frequency disturbances in BI and C4A allotypes but not C4B allotypes. Whilst this study has not provided evidence of a strong marker gene for PPT, it does not preclude the involvement of the MIIC in this condition. These data show disturbances in complement allotype frequencies, suggesting that the class III region may provide a useful focus for further study of this pathology.