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PubMed1990

Phagocytosis of Mycobacterium tuberculosis is mediated by human monocyte complement receptors and complement component C3.

We have examined the receptor-ligand interactions and the method of phagocytosis of virulent Mycobacterium tuberculosis by human monocytes. mAb against complement receptors (CR) inhibit adherence and phagocytosis of M. tuberculosis in fresh nonimmune serum. A mAb against the type 1 CR (CR1) inhibits adherence of M. tuberculosis by 40 +/- 5%, and three different mAb against the type 3 CR (CR3) each inhibit adherence by 39 +/- 5% to 47 +/- 4%. A mAb against CR1 used in combination with one of the three mAb against CR3 inhibits adherence by up to 64 +/- 7%. Most strikingly, two mAb used in combination against CR3 inhibit adherence by up to 81 +/- 2%. mAb against other monocyte surface Ag do not significantly influence adherence. In like fashion, mAb against CR but not other monocyte surface Ag inhibit adherence of preopsonized M. tuberculosis in the presence of heat-inactivated serum. By electron microscopy, monocytes ingest all M. tuberculosis that adhere in the presence of nonimmune serum; mAb against CR3 markedly inhibit ingestion. In contrast to CR, the FcR and the beta-glucan-inhibitable receptor for zymosan play little or no role in mediating M. tuberculosis adherence or ingestion. Adherence of M. tuberculosis is serum-dependent, requiring greater than or equal to 2.5% serum for optimal adherence. Heat inactivation of serum markedly reduces adherence of M. tuberculosis (75.5 +/- 7%) and preopsonization of bacteria enhances adherence by 2.9 +/- 0.4-fold. Adherence is also markedly reduced in C3- or factor B-depleted serum; repletion with C3 or factor B increases adherence by 2.1 +/- 0.4-fold and 1.86 +/- 0.05-fold, respectively. Fab anti-C3 IgG markedly inhibits monocyte adherence of preopsonized M. tuberculosis (71 +/- 1%). C component C3 is fixed to M. tuberculosis by the alternative C pathway as determined by a whole bacterial cell ELISA. Human monocytes ingest M. tuberculosis by conventional phagocytosis as viewed by electron microscopy. This study demonstrates that human monocyte CR1 and CR3 mediate phagocytosis of M. tuberculosis and C component C3 in serum is acting as the major bacterium-bound ligand.

Antibodies, Monoclonal↗

PubMed2003

Complement receptors type 1 (CR1, CD35) and 2 (CR2, CD21) cooperate in the binding of hydrolyzed complement factor 3 (C3i) to human B lymphocytes.

The C3b-binding receptor, CR1/CD35, supports CR2/CD21-mediated activation of complement by human B lymphocytes, possibly by associating with CR2 to promote or stabilize the binding of hydrolyzed C3 (C3i), the primary component of the AP convertase, C3i-Bb. To evaluate this hypothesis, we examined the uptake kinetics and binding equilibria for C3i dimer interaction with human blood cells in the absence and presence of CR1- and CR2-blocking mAb. C3i displayed dual uptake kinetics to B lymphocytes, comprising of rapid binding to CR1 and slower binding to CR2. The forward rate constants (k(1)) for CR1 and CR2, operating independently, differed ca. 9-fold (k(1)=193+/-9.4 and 22.2+/-6.0 x 10(3) M(-1)s(-1), respectively). Equilibrium binding of C3i to B lymphocytes was also complex, varying in strength by ca. 13-fold over the C3i concentration range examined. The maximum association constant (K(a, max)=109+/-27.2 x 10(7) l/mole) was ca. 9- and 6-fold greater, respectively, than those for CR1 or CR2 acting alone (K(a)=13.2+/-5.3 and 18.5+/-3.5 x 10(7) l/mole). The high avidity of the CR1-CR2 complex for C3i is consistent with its rates of C3i uptake and release being determined by CR1 and CR2, respectively.

B-Lymphocytes↗

PubMed1981

Hemolysis by the complement of tanned erythrocytes coated with cobra venom factor: a sensitive method to detect the alternative complement pathway activity of serum.

Sheep (Esh), human (Ehu), rabbit (Erab) or guinea pig (Egp) erythrocytes were treated with tannic acid and coated with cobra venom factor (CoVF), which activates the alternative complement pathway (ACP). Tanned erythrocytes (TE) coated with CoVF (TECoVF) were efficiently hemolyzed by guinea pig serum l(GPS) and/or rabbit serum (RabS) in Mg2+-EGTA-GVB (gelatin veronal-buffered saline containing 2 mM MgCl2 and 10 mM ethyleneglycol-bis(beta-aminoethyl ether)N,N'-tetraacetate). The reactivity of TEsh-CoVF, TEhu-CoVF and TErab-CoVF to the ACP of guinea pig and/or rabbit increased with the increased amount of CoVF fixed on TE until it was sensitive enough to be hemolyzed by serum diluted over 80 times in Mg2+-EGTA-GVB. The hemolysis of TECoVF by GPS was confirmed to be the result of ACP activation by the findings that the reaction was inhibited in EDTA-GVB, heating of GPS at 50 degrees C diminished its hemolytic potency, and fractions of factor B and factor D were essential to the sensitization of TECoVF for hemolysis by GPS in EDTA-GVB. On the other hand, none of the TE coated with CoVF were hemolyzed by human serum (HuS) diluted over 1 : 40. Although the low efficiency of HuS in TE-CoVF hemolysis remains to be explained, TE-CoVF will be useful for the detection of ACP activity of guinea pig and rabbit sera.

Animals↗

PubMed1992

Studies on activation and levels of haemolytic complement of buffalo (Bubalus bubalis). II. Alternate complement pathway activity in serum.

Buffalo serum caused lysis of unsensitized red blood cells (RBC) of sheep, goat, rabbit and guinea-pig. There was minimal lysis of cattle RBC, and homologous RBC were resistant. Lysis of sheep and goat RBC was the result of natural antibodies as adsorption with respective RBC and addition of 8 mmol ethylene glycolbistetraacetate (EGTA) in diluent completely abrogated the haemolytic activity. The lysis of guinea-pig and rabbit RBC was only partially decreased by these treatments, indicating the presence of alternate complement pathway (ACP) activity in buffalo serum. The guinea-pig RBC were the most sensitive to lysis, and 50% CH titre units above 40 ml-1 of serum were obtained. The haemolytic activity of buffalo C for unsensitized guinea-pig RBC was reduced from 47 CH50 units to an undetectable level by heating at 50 degrees C for 20 min and at 56 degrees C for 4 min. Similarly, treatment with zymosan also inhibited this haemolytic activity. Maximum activation of buffalo ACP occurred in the presence of 4 mmol Mg2+ in the diluent. Using standardized conditions, ACP activity was determined in sera of 98 healthy buffaloes of different age groups from 1 month to 12 years. Even young calves less than three months of age showed considerable ACP activity (45.60 +/- 1.21 CH50 units ml-1) which increased with age. The peak mean values of 79.79 +/- 1.45 CH50 units was recorded in 2 to 4-year-old animals. However, in all the 11 animals above 4 years of age, the haemolytic activity was greatly reduced and was even less than that in 1 to 3-month-old buffalo calves.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1995

Cleavage of the third component of complement (C3) by mannose-binding protein-associated serine protease (MASP) with subsequent complement activation.

We have previously shown that a novel C1s-like serine protease termed MBP-associated serine protease (MASP) is responsible for activation of the complement cascade initiated by mannose-binding protein (MBP). In this communication, we report that MASP is unique in having the proteolytic capacity to cleave C3 with subsequent activation of the alternative pathway, a capacity which C1s lacks.

Carrier Proteins↗

PubMed1988

Comparison between complement and melittin hemolysis: anti-melittin antibodies inhibit complement lysis.

A comparison is made between the hemolytic actions of melittin and the ninth component of complement (C9). Melittin and C9 produce "pores" of similar effective radius in erythrocytes under standardized conditions, and their hemolytic action is suppressed by metal ions at similar concentrations, suggesting a common mechanism. Polyclonal anti-melittin immunoglobulin G (IgG) produced in rabbits retards hemolysis mediated by human C9 in a specific manner. Such antibodies react in several immunoassays with human and monkey C9 but not with C9 from lower animals, and no inhibition of lysis mediated by C9 molecules from these animals is observed. Thus, it is unlikely that anti-melittin IgG reacts with a structural element, such as an amphipathic helix, on human C9 since such structures are also predicted to exist in other C9 molecules. Human C9 and melittin block cross-reactivity in a dose-dependent manner, and anti-melittin IgG recognizes an epitope located between amino acid residues 245 and 390 of human C9 on "Western" blots. Comparison of the melittin and human C9 sequences indicates two regions of complete homology, a tetrapeptide at positions 292-295, and a pentapeptide at positions 527-531 in human C9, corresponding to residues 8-16 in melittin. Inhibition of hemolysis is not caused by blocking of C9 binding to the C5b-8 complex; rather the antibody must dissociate from the bound C9 before lysis ensues, indicating that it interferes with a postbinding event. It is proposed that anti-melittin binds to a conformational epitope on native, folded human C9 and thereby retards unfolding of the molecule, which is required for membrane insertion and hemolysis.

Antibodies↗

PubMed1997

Mechanisms of complement resistance induced by non-lethal complement attack and by growth arrest.

Non-lethal complement (C) attack on K562 cells has been shown to induce a transient resistance to lethal amounts of C. We have previously shown that incubation of K562 with phorbol 12-myristate 13-acetate (PMA) caused an increase in both CD59 expression and resistance to C killing and we were interested to examine whether non-lethal C attack caused a similar effect. We here demonstrate that expression of the C inhibitors decay-accelerating factor (DAF), membrane cofactor protein (MCP) and CD59 was unaltered on K562 after non-lethal C attack and that neutralization of these inhibitors with specific blocking antibodies did not reverse the induced resistance. In an effort to understand the mechanisms of resistance we searched for other conditions that might induce C resistance in K562 cells. Growth-arrested cells showed a similar degree of resistance to C killing. The levels of DAF and MCP on these cells were unaltered whereas expression of CD59 was markedly reduced. Non-lethal C attack on these growth-arrested cells induced a further increase in resistance to C killing, suggesting that the mechanisms of resistance were not identical. Indeed, resistance of non-lethally attacked cells was completely lost within 8 hr of attack whereas resistance of growth-arrested cells was detectable for up to 48 hr after returning to cell cycle. These data demonstrate that C resistance induced by two distinct strategies is not mediated by the known membrane C inhibitors. Resistance may be a result of the expression of a novel inhibitor or due to metabolic depletion, a likely common consequence of non-lethal C attack and induction of growth arrest, implying that cells take an active role in C-mediated killing.

Cell Cycle↗

PubMed1989

Structural homology of complement protein C6 with other channel-forming proteins of complement.

The amino acid sequence of the amino-terminal half of the complement protein C6 has been found to show overall structural homology with the homologous regions of the channel-forming proteins C7, C8 alpha, C8 beta, and C9. In addition, two specific cysteine-rich segments common to the amino-terminal regions of C7, C8 alpha, C8 beta, and C9 also occur in their expected positions in C6, suggesting functional significance. Two cDNA clones encoding C6 were isolated from a human liver library in the bacteriophage vector lambda gt11. The predicted protein sequence contains an apparent initiation methionine and a putative signal peptide of 21 residues, as well as a site for N-glycosylation at residue 303. The sequence of the C6 protein reported here has 47-52% similarity with C7, C8 alpha, C8 beta, and C9, as well as 31-38% similarity with thrombospondin, thrombomodulin, and low density lipoprotein receptor. The sequence data have been interpreted by using computer algorithms for estimation of average hydrophobicity and secondary structure.

Amino Acid Sequence↗

PubMed1983

Localization of complement component 3 on Streptococcus pneumoniae: anti-capsular antibody causes complement deposition on the pneumococcal capsule.

We have previously shown that complement component 3 (C3) deposited onto encapsulated Streptococcus pneumoniae by anti-capsular antibody (Ab) is a more efficient opsonin in vitro and in vivo than C3 deposited by anti-cell wall Ab (Brown et al., J. Clin. Invest. 69:85-98, 1982). In the present study, we explored the cellular location of C3b molecules that differ in opsonic efficiency by using avidin-ferritin to localize biotinylated Ab and C3 molecules on S. pneumoniae for electron microscopy. Anti-cell wall Ab and C3b molecules deposited by this Ab on unencapsulated S. pneumoniae were localized to S. pneumoniae cell walls. Anti-capsular Ab and C3b deposited by this Ab were seen in clusters on encapsulated S. pneumoniae at a distance from the cell wall. However, no avidin-ferritin staining of encapsulated S. pneumoniae was seen on incubation with biotinyl-anti-cell wall Ab, biotinylated C3 fixed by anti-cell wall Ab, or nonimmune serum containing biotinyl-C3. In each case, uptake of the biotinylated component was proven by radioactivity measurements, since biotinylated Ab and C3 were also radiolabeled with 125I. When avidin-ferritin did not bind to biotinylated components. Ouchterlony analysis indicated that C3 was bound to cell wall components on the encapsulated organisms. Thus, we conclude that, for encapsulated S. pneumoniae, opsonically efficient C3b molecules, deposited by anti-capsular Ab, are located on the S. pneumoniae capsule, whereas the opsonically inefficient C3b molecules deposited by anti-cell wall Ab or nonimmune serum are located on the cell wall. A major reason for the increased virulence of encapsulated compared to unencapsulated S. pneumoniae is that, in the absence of anti-capsular Ab, the S. pneumoniae capsule interferes with the recognition of cell wall-bound C3b molecules by phagocytic cell receptors.

Antibodies, Bacterial↗

PubMed1986

Circadian and diurnal variation of circulating immune complexes, complement-mediated solubilization, and the complement split product C3d in rheumatoid arthritis.

Nine patients with active classical rheumatoid arthritis (ARA criteria) were studied with reference to circadian variation of immunological and clinical parameters. Complement-mediated solubilization (CMS) of immune complexes (IC) and the level of circulating IC were found to be inversely related with low CMS and increased IC levels in the morning, and vice versa in the afternoon. Bed rest and exercise did not influence these fluctuations. The C3d concentration in plasma was increased but showed no diurnal or circadian periodic fluctuations when the levels were corrected for fluctuations in plasma albumin concentration. Clinical assessment by means of pain score exhibited marked variations, with high scores in the morning, and lower in the daytime, whereas measurements of Ritchie's joint index showed no consistent pattern. The circadian variations in CMS, serum IC and clinical parameters indicate the need to collect blood specimens and perform clinical examinations of patients at a fixed time of day.

Adult↗

PubMed1997

Complement activation and thromboxane secretion by liposome-encapsulated hemoglobin in rats in vivo: inhibition by soluble complement receptor type 1.

Intravenous administration of liposome-encapsulated hemoglobin (LEH) in rats led to an early (within 15 min) decline of hemolytic complement (C) activity in the plasma along with a significant, parallel rise in thromboxane B2 (TXB2) levels. The TXB2 response was inhibited by co-administration of soluble C receptor type 1 (sCR1) with LEH, as well as by C depletion with cobra venom factor. These observations provide evidence for a causal relationship between LEH-induced C activation and TXB2 release, and suggest that sCR1 could be useful in attenuating the acute respiratory, hematological and hemodynamic side effects of LEH described earlier in the rat.

Animals↗

PubMed1991

Two major serum components antigenically related to complement factor H are different glycosylation forms of a single protein with no factor H-like complement regulatory functions.

Factor H is a 150-kDa serum glycoprotein with key regulatory functions in the alternative pathway of complement activation. Two glycoproteins with a molecular mass of approximately 42 and 37 kDa that react with an antiserum against factor H were purified from human plasma. The two glycoproteins have identical N-terminal amino acid sequences but differ in glycosylation. Sequence comparisons indicated that they both correspond to a 1.4-kb mRNA recently cloned from human liver cDNA. The serum concentration of the two glycoproteins together was estimated to be approximately 40 mg/liter. They were found not to exert factor H-like regulatory functions in the alternative pathway. Thus, the 42-kDa glycoprotein described here appears to be distinct from the previously characterized factor H-related protein of similar size, suggesting that human serum contains two factor-H related molecules which both have a molecular mass of 41 to 43 kDa but which differ largely in structure.

Amino Acid Sequence↗

PubMed1990

Multiple signal messengers generated by terminal complement complexes and their role in terminal complement complex elimination.

The best established function of C5b-9 is the ability to lyse or kill cells after assembly in the plasma membrane. In addition to this cytolytic function, increasing evidence suggests that C5b-9 also stimulate a variety of cell functions in vitro. Relatively little is known about the C5b-9 signals responsible for cell activation other than a transient increase in cytosolic Ca2+ primarily due to Ca2+ influx that have been determined in a cell population. In this report, signal messenger generation in Ehrlich cells by the sublytic terminal complement complexes (TCC), C5b-9, C5b-8, and C5b-7, was further examined, as well as the role of signal messengers in stimulating elimination of TCC from the cell surface. Changes in cytosolic Ca2+ were monitored in individual cells after a single dose of C5b-9 by digital imaging fluorescence microscopy that revealed oscillations in cytosolic Ca2+ over a period of 10 min. Sublytic C5b-9 substantially increased protein kinase C (PKC) activity at an external Ca2+ concentration of 1.5 mM. C5b-9-mediated PKC activation could be inhibited by 60 to 80% when external Ca2+ was reduced to 0.015 mM. C5b-8, but not C5b-7, activated PKC to a lesser extent. C5b-8 and C5b-7 also stimulated an increase in cAMP. Rapid elimination of TCC known to be stimulated by Ca2+ signal was partially inhibited by protein kinase inhibitors, H-7 and to a lesser extent by HA1004, suggesting a role for PKC in the elimination response. TCC elimination was not accelerated by agents that increase cAMP.

Calcium↗

PubMed1986

Complement effects on the infectivity of Plasmodium gallinaceum to Aedes aegypti mosquitoes. I. Resistance of zygotes to the alternative pathway of complement.

Gametocytes are the intraerythrocytic stages of malaria parasites that infect mosquitoes. When gametocytes of the chicken malaria parasite Plasmodium gallinaceum are ingested by a mosquito they become extracellular in the mosquito midgut, form gametes, and fertilize within 10 to 15 min after the insect has taken a blood meal. Gametocytes of P. gallinaceum were infectious when fed to Aedes aegypti mosquitoes in blood meals containing native serum from chickens or from the non-host species, man or sheep. Gametocytes stimulated to undergo gametogenesis and to fertilize in vitro were also infectious when fed to mosquitoes in native chicken serum. However, native serum from most non-host species, including sheep and man, suppressed the infectivity of newly fertilized zygotes to mosquitoes and lysed the zygotes in vitro. These effects were shown to be due to the activity of the alternative pathway of complement (APC) in the serum of the non-host species. After mild trypsin treatment, the zygotes of P. gallinaceum no longer infected mosquitoes in the presence of native chicken serum, although in heat-inactivated chicken serum their infectivity was normal. We conclude that trypsin-sensitive components on the zygotes surface protect them from destruction by the APC of their native host. The ability of gametocytes of P. gallinaceum to infect mosquitoes in the presence of native human serum is probably due to proteases that inactivate the APC of human serum before the gametes and zygotes emerge as extracellular parasites in the blood meal.

Aedes↗

PubMed1978

Complement lysis: evidence for an amphiphilic nature of the terminal membrane C5b-9 complex of human complement.

The terminal, membrane-derived C5b-9 complex of human complement (C) is an apparently hollow, cylindrical macromolecule vertically oriented on the target membrane. In the present study, an antiserum to the complex has been used to probe its immunobiochemical properties. "Neoantigenic" determinants characteristic of the complex have been detected, which are absent on native C5-C9 molecules. Evidence that the C5b-9 complex is an amphiphilic molecule that possesses apolar, detergent-binding surfaces has been obtained by using charge-shift crossed immunoelectrophoresis, and by direct demonstration of Triton X-100 binding to the complex in quantitative immunoelectrophoresis. By the same criteria, serum C5, C6, and C9 are hydrophilic molecules. The results indicate that assembly of C5-C9 into the terminal membrane C5b-9 complex is accompanied by conformational changes in the individual C components that lead to the exposure of apolar molecular regions in the complex. It is proposed that this constitutes the basis for the lipid-binding properties of the macromolecule, which enable it to become inserted into biologic and artificial lipid membranes with apparent generation of a transmembrane pore.

Animals↗

PubMed1982

Receptors for complement on echinoid phagocytes. II. Purified human complement mediates echinoid phagocytosis.

The ingestion of sheep erythrocytes (E) coated with specific IgM antibody (EA) and various purified human complement components (EAC 1, EAC 14, EAC 142, EAC 1423b, EAC 43b) by echinoid phagocytes was examined. E, EA, EAC 1, EAC 14 and EAC 142 were ingested at a similar and very low level, while a strong opsonic effect was found by coating red cells with purified C 3 (EAC 1423b and EAC 43b). When erythrocyte-bound C 3b was converted to the hemolytically inactive C 3bi, the opsonic effect was markedly increased. Conversion of C 3bi to C 3d resulted in a total loss of opsonic activity. A similar response pattern was found when binding of erythrocytes to mouse macrophages was recorded. Since it cannot be ruled out that phagocytes convert C 3b to C 3bi by endogeneous C 3 inactivator, it is concluded that echinoid phagocytes display CR3 (C 3bi) and possibly also CR1 (C 3b) receptors, while CR2 (C 3d) receptors are lacking.

Animals↗

PubMed1980

Circulating immune complexes, complement and complement component levels in childhood Hodgkin's disease.

Serum levels of circulating immune complexes (CIC) assayed by the Raji cell radioimmunoassay, total haemolytic complement (TCH50), Clq and C3 were correlated with clinical stage, histological type, age, sex and treatment of eighty-six children with Hodgkin's disease over a period of 4 years. Most significant findings were the changes of levels of CIC, TCH50, Clq and C3 during disease activity and following treatment. Significant perturbations were also seen in association with relapse. Levels of C and CIC were significantly elevated (P less than 0.001) at the time of diagnosis prior to splenectomy and/or any treatment. In the group before treatment, 81 percent of CIC levels were above 16 micrograms/ml with a maximum value of 1120 micrograms/ml. During treatment 33 percent were still above normal with a maximum of 320 micrograms/ml. Within 1 year after cessation of treatment, 37 percent also remained above normal levels with a maximum of 240 micrograms/ml. At relapse prior to treatment, 63 percent were again elevated with a maximum of 1280 micrograms/ml. The most significant difference on TCH50 levels relates to treatment periods. Sera of patients with active disease who are previously untreated show elevation of TCH50 levels (P less than 0.001) (average 127 CH50 mu/ml. During and after treatment eht TCH50 levels drop to 96 and 102 CH50 mu/ml, as compared to normal control of 100 CH50 mu/ml. In sera of patients at the first, second or third relapse, the combined TCH50 levels are significantly different from controls and across treatment periods (P less than 0.005).

Adolescent↗

PubMedDate not supplied

Complement mediated solubilization: role of the complement in the clearance of circulating immune-complexes.

In 1975, Miller and Nussenzweig described a new function of the Complement (C'): the Capacity of this substance to solubilize "in vitro" antigen/antibody complexes previously formed. Subsequent studies of these authors and other researches (particularly Takahashi and his group) demonstrated that this process is mediated by activation of the alternative way of C', although it is faster when the classic way is involved. Basically, thanks to the Takahashi and group studies, it has been possible to know in detail the intimate mechanism of this phenomenon, usually known demonstrated that the key of all this process lies in the generation, through the C' alternative way, of numerous molecules of C3b that deposit over the antigen/antibody complexes (Ag/Ac), causing the breakage of the necessary mesh for such complexes to precipitate, which leads to formation of small immunocomplexes (IC) very rich in C3b which turn soluble again. ICs solubilized in this way suffer important physicochemical and biological changes, and transform into substances without inflammatory power that are not able to activate C' nor to interact with C3b receptors present in a great number of blood cells. However, they are captured by Kupffer cells in the hepatic sinusoids and quickly catabolized. CMS is closely related with another similar phenomenon, the Immuno-Precipitation inhibition (IPI), described by Schiferli and his group in the early 80's.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗