Complement Activating Factor Research Articles

Complement Evasion Protects FCoV from Virus Clearance Within Prototypic FIP Lesions

Feline infectious peritonitis (FIP) is a fatal disease in cats caused by infection with feline coronavirus (FCoV). Despite severe inflammatory changes, defense mechanisms fail to achieve virus clearance. Some studies focused on various immune evasion mechanisms, but none of these studies elucidated the inefficacy of the complement system, which is one major player in FIP-associated immune pathogenesis. This study aimed to investigate the involvement of complement-regulating factors (CRFs). CRFs help modulate the immune response and prevent host tissue damage. Archived tissue samples from 31 deceased, FIP-affected cats were evaluated using multiplex immunohistochemistry for the spatial expression of the complement-regulating factors CD46 and CD59 in association with FIP lesions and their colocalization with complement-activating factor C1q and membrane attack complex C9 in relation to the presence and proximity of FCoV-infected cells. The FIP lesions of all 31 cats exhibited marked expression of both complement-regulating factors in proximity to FCoV-infected macrophages. Moreover, their expression in all 31 animals was significantly lower than the expression of the complement-activating factors C1q and C9 compared to areas farther distal to FCoV-infected cells. In conclusion, FCoV-infected macrophages in cats with FIP appear to use autocrine and paracrine expression of complement-regulating factors in their immediate environment to shield themselves from destruction by the complement system.

The bacteria binding glycoprotein salivary agglutinin (SAG/gp340) activates complement via the lectin pathway

Salivary agglutinin (SAG), also known as gp-340 and Deleted in Malignant Brain Tumours 1, is a glycoprotein that is present in tears, lung fluid and mucosal surfaces along the gastrointestinal tract. It is encoded by the Deleted in Malignant Brain Tumours 1 gene, a member of the Scavenger Receptor Cysteine Rich group B protein superfamily. SAG aggregates bacteria thus promoting their clearance from the oral cavity and activates the complement system. Complement proteins may enter the oral cavity in case of serum leakage, which occurs after mucosal damage. The purpose of this study was to investigate the mode of complement activation. We showed a dose-dependent C4 deposition on SAG-coated microplates showing that either the classical or lectin pathway of complement was activated. Antibodies against mannose binding lectin inhibited C4 deposition and SAG induced no C4 deposition in MBL deficient sera showing SAG activated complement through the MBL pathway. Periodate treatment of SAG abolished MBL pathway activation consistent with an involvement of SAG glycans in complement activation. This provides the first evidence for a role of SAG in complement activation through the MBL pathway and suggests a potential role of SAG as a complement activating factor at the mucosal epithelia.

Elevation of Adipsin, a Complement Activating Factor, in the Mouse Placenta During Spontaneous Abortion

The complement system is thought to be precisely regulated during pregnancy. We have examined specific gene profiles in mouse placentas causing spontaneous abortion and found notable up-regulation of adipsin, a complement activating factor. The aim of the present study was to determine the basic kinetics and localization of adipsin in the placenta and the difference in complement activity between normal placentas and placentas of abortuses. Normal and spontaneously absorbed implantation sites obtained from naturally-mated mouse uteri on days 10.5 and 14.5 of pregnancy were processed for histologic studies and protein purification. Adipsin immunoreaction was detected at the decidua basalis in normal placentas and additionally at the placental labyrinth in the absorbed placentas. The quantity of adipsin was increased in the absorbed placentas compared with the normal placentas. In concert with the increase in adipsin, the amounts of complement component 3 and degradation products were elevated and complemental activity was up-regulated in the absorbed placenta. These findings suggest that local expression of adipsin has a reproductive effect at the feto-maternal interface and possibly plays a role in spontaneous abortion.

Characterization of Bovine Serum Factor Triggering the Lysis of Liposomes via Complement Activation.

Our previous studies have shown that the degree of damage to a liposome corresponds to the variability of the animal species from which the serum comes, and that a complement activating factor (CAF) plays an important role in inducing the activation of the complement system, ultimately leading to the lysis of the liposomes. In this study, our attention focused on the characterization of the bovine serum factor (bCAF) that is involved in complement-mediated immune lysis of the liposome. The active fraction containing CAF partially purified with PEG and ammonium sulfate results in marked activation of the complement system via the alternative pathway when interacted with CAF-depleted serum, whereas the active fraction or CAF-depleted serum alone does not activate the complement. The interaction between lipopolysaccharide (LPS), heparin, zymosan or their mixture in place of CAF and CAF-depleted serum does not result in any significant activation of the complement system. Results from pretreatment with rabbit anti-bovine IgM IgG and rabbit anti-bovine IgG IgG indicate that activation of the complement system is not attributable to the antibody which is generally involved in activation of complement via the classical pathway. The results have further been proven by pretreatment with Concanavalin A (Con A) sepharose and protein G sepharose ruling out the possibility of antibody-mediated activation of complement. Our studies on collagenase and trypsin digestion demonstrate that the relative activity of CAF does not diminish with increase in collagenase concentration, and decreases with increase in trypsin concentration, strongly indicating that CAF does not have a collagen-like domain in its structure. The relative activity of CAF is dramatically inhibited after reduction with 2-mercaptoethanol (2-ME), clearly demonstrating that CAF is sensitive to reduction with 2-ME and confirming a sulhydryl-dependent protein. The optimal activity of CAF is observed in the range of 35-45 degrees C and its half-life at 37 degrees C is about 105 h. Furthermore, the relative activity of CAF increases and gradually approaches a plateau level with the increase of Mg2+ concentration. Obviously, complement activation induced by CAF depends on adequate Mg2+ concentration, confirming that this dependence is characteristic of the alternative pathway.

Killing of rat glial cells by complement: Deficiency of the rat analogue of CD59 is the cause of oligodendrocyte susceptibility to lysis

In an effort to understand the mechanisms of complement-mediated injury of the myelin/oligodendrocyte complex in demyelinating disease, we have examined the lytic susceptibility of rat glial cells in culture. It is known that rat oligodendrocytes are extremely sensitive to the lytic action of autologous complement, whereas other cells in the same culture system, including type II astrocytes which derive from the same progenitor cell, are relatively insensitive. Here we demonstrate that the complement sensitivity of oligodendrocytes is associated with a lack of expression of a complement-regulatory protein, the rat homologue of human CD59, and that complement resistance can be restored by the incorporation of purified rat CD59 into the cell membrane. Furthermore, neutralisation of rat CD59 on complement-resistant astrocytes renders them susceptible to lysis. Immature oligodendrocytes were resistant to complement attack yet did not express CD59, suggesting that a complement-activating factor appears on the membrane during oligodendrocyte maturation.

Interactions of Plasmodium berghei-infected erythrocytes with complement.

Incubation of radioactively labeled parasitized (Plasmodium berghei) erythrocytes (PE) with adherent peritoneal exudate cells in the presence of 10% (v/v) fresh mouse serum (NMS) resulted in the uptake of a proportion of radioactive material (PE). Inactivation of the added serum by heat or zymosan treatment resulted in diminished uptake of radioactivity. These results suggest that PE activated complement. Incubation of fresh NMS with PE reduced the hemolytic complement level of the serum as shown by its subsequent decreased ability to lyse antibody-coated rabbit red blood cells. No such effect was found when uninfected erythrocytes from either infected or uninfected blood were preincubated with fresh NMS. Thus, PE or PE-derived material activated complement. Addition of EGTA during incubation of fresh NMS with PE did not inhibit the decrease in complement level. This indicated that complement was activated by the alternative pathway. Complement levels decreased even when fresh NMS and PE were incubated in the presence of EDTA (which inhibits both classical and alternative pathway activation), suggesting that a complement activating factor (or a complement inhibitor) was released from the PE. However, lysis of PE after incubation with either fresh rabbit or guinea pig serum did not occur unless anti-mouse erythrocyte antibody was added. The production of a complement-activating factor by PE might explain part of the decreasing complement levels during infection and might enable the parasite to escape from a complement-mediated defense mechanism of the host.

Activation of the alternative complement pathway by extracts of cotton dust.

Extracts of cotton dust were tested for their ability to activate the alternative complement pathway in fresh normal human serum (NHS). Alternative pathway activation was determined by a haemolytic assay utilizing glutathione-sensitized human erythrocytes, consumption of alternative pathway components in terms of alternative pathway CH50 units and an immunoelectrophoretic assay to detect split products of activation of factor B. All assays were performed under conditions that have been shown to block the initial steps of classical pathway activation but permit activation of the alternative complement pathway. Results demonstrate that the cotton dust extracts could consume alternative complement pathway proteins in a dose-response manner. The complement activating factor is probably endotoxin since a cotton dust extract obtained by an extraction method for endotoxin yielded the greatest activity.

Studies on the mechanism of haemopoietic stem cell (CFUs) mobilization. A role of the complement system.

A variety of substances can mobilize haemopoietic stem cells (CFUs) into the peripheral blood. In this study the involvement of the complement system in the mobilization process was investigated. Pretreatment of mice with the complement-activating factor of cobra venom (CoF), which lowered the serum C3 levels to 10-25% of the normal value, could completely prevent CFUs mobilization induced by high doses of CoF, endotoxin (ET) from Salmonella typhosa, inulin, zymosan and the proteolytic enzymes proteinase and trypsin. On the other hand, mobilization induced by the polyanions dextran sulphate and the copolymer of polymethacrylic acid and styrene could not be prevented, or at least affected only slightly. There appears to be a relationship between the extent of decomplementation by CoF and the extent of CFUs mobilization induced by ET. The results indicate that certain agents mobilize CFUs via the complement system, whereas other agents induce CFUs mobilization independent of the availability of complement components.

Increased susceptibility ofTrypanosoma lewisi infected, or decomplemented rats toSalmonella typhimurium

Rats infected with Trypanosoma lewisi or decomplemented by injection of cobra venom factor or complement activating factor of trypanosomes were found to be more susceptible to infection with Salmonella typhimurium. Decomplemented rats subsequently infected with T. lewisi developed higher blood parasitemia than did normal T. lewisi infected rats.

FREE FATTY ACIDS, COMPLEMENT ACTIVATION, AND POLYCLONAL B-CELL STIMULATION AS FACTORS IN THE IMMUNOPATHOGENESIS OF AFRICAN TRYPANOSOMIASIS

Human and animal forms of African trypanosomiasis are characterised by sustained hypocomplementæmia, gross hypergammaglobulinæmia M, and profound immunosuppression. It is suggested that this hypocomplementæmia is probably due to the action of a trypanosome-derived complement-activating factor and that the elevated IgM levels may be the combined result of this decomplementation, together with a subsequent failure of the normal IgM-to-IgG antibody switch mechanism and polyclonal B-lymphocyte activation by a trypanosome-generated mitogen The immunosuppression in this disease may be a result of the collective immunosuppressive effects of trypanosome-derived immune-modulating free fatty acids, polyclonally stimulating B-cell mitogen, and complementactivating factors.

Activation of complement by trypanosomes

Factors exhibiting anti-complementary activity released from trypanosomes after incubation at 20 degrees C were described. The active material was shown to consume the first component of bovine complement. While the anti-complementary factor(s) from T. lewisi could activate bovine, human and guinea pig complement, the factor(s) from T. congolense was observed to activate bovine complement, but not guinea pig and only slightly human complement. The roles of complement activating factor(s) of trypanosomes in the pathology of the disease are discussed.