PubMed Health⌕ Search

Biomedical subjects

T Seya

Publications and source records attributed to T Seya.

At least 19 recordsLinked to original sources
PubMed1992

Polymorphism and proteolytic fragments of granulocyte membrane cofactor protein (MCP, CD46) of complement.

Human granulocytes (polymorphonuclear leucocytes, PMN) possess a membrane cofactor protein (MCP, CD46), which is structurally and functionally distinct from the MCPs of other cell types: it shows a single broad band of 56-80 kDa (without the doublet pattern characteristic of MCP) on SDS/PAGE and has less affinity for complement component C3b. We purified PMN MCP using monoclonal antibodies in order to study the molecular differences between it and other MCPs. Several forms of PMN MCP with size heterogeneity were noted on SDS/PAGE and by immunoblotting. O-Glycanase treatment decreased this heterogeneity, yielding a fast-migrating component identical in position on SDS/PAGE to the O-glycanase-treated MCP of other cells. The cell-specific variation of MCP, therefore, arises from post-translational glycosylation and not from a difference in primary structure. The Factor I cofactor activity of PMN MCP was more efficient in cleaving the methylamine-treated complement components C4/C3 than was MCP from other cells, which shared a similar potency of cofactor activity on a weight basis. Two types of small-form PMN MCP were identified during purification. These were 42 kDa and 30 kDa in size; the former was recognized by M177 (a monoclonal antibody against the active site marker), possessed N-linked sugars [located on the short consensus repeats (SCRs)] but not O-linked ones (on the Ser/Thr-rich region), and retained cofactor activity for C3b/C4b cleavage, similar in potency to that of other MCPs. The functionally active soluble form of MCP was observed specifically in PMN. Protease inhibitors did not inhibit liberation of the fragments, although the generated fragments became susceptible to serine proteases. The findings show that the SCRs are the functional domain of MCP and that the MCP proteolysis found only in PMN may modulate the properties of PMN MCP. In conclusion, the structural features of PMN MCP largely reflect a variability in the O-linked sugars, and the decreased affinity for C3b may be in part attributable to proteolysis.

Antigens, CD↗
PubMed1992

Two modes of homologous C3 deposition on Ramos Burkitt's lymphoma cell substrains co-expressing DAF (CD55), CD59, and CR2 (CD21), and on cells lacking them.

We established decay-accelerating factor (DAF)/CD59-positive and -negative substrains of a human B cell line, Ramos, R(DAF+/CD59+) and R(DAF-/CD59-) respectively. Unexpectedly, treatment of R(DAF+/CD59+) cells with Mg2(+)-EGTA-serum resulted in efficient C3 deposition, while treatment of R(DAF-/CD59-) cells did not. All six substrains of R(DAF-/CD59-) cells were CR2-negative, and treatment of the cells with M177 [a membrane cofactor protein (MCP) cofactor-blocking antibody] and/or acidic buffer only minimally affected the extent of C3 deposition. However, when R(DAF-/CD59-) cells were pretreated with M177 followed by incubation with low conductivity (3 mS) Mg(2+)-EGTA-serum, C3 deposition leading to effective cytolysis was provoked. On the other hand, all seven R(DAF+/CD59+) substrains were CR2-positive and could potentially induce C3 autoactivation without cytolysis under physiological conditions. Both M177 and pH again minimally affected the extent of C3 deposition. However, conductivity altered the sensitivity to C3: at under 3.0 mS, R(DAF+/CD59+) cells became almost insensitive to alternative pathway-mediated C3 deposition. Anti-CR2 partially inhibited C3 deposition on R(DAF+/CD59+) cells and C3 deposition was abrogated on the CR2-lacking R(DAF-/CD59-) cells, suggesting that CR2 was associated with the deposition of C3. These results, together with the finding that fluid phase activation of complement did not enhance C3 deposition, suggest that there are two distinct modes of spontaneous homologous C3 deposition on human lymphoma cells. In one case, CR2 or its related molecules participates in C3 deposition overcoming the protective function of DAF/MCP and this type of C3 deposition is maximized under physiological conditions. In the other case, C3 deposition is induced by another homologous C3 activator that becomes functional under low conductivity conditions and the absence of DAF/MCP. These two modes of homologous alternative pathway activation would explain the reported instances of spontaneous C3 deposition on human B lymphoid cell lines (under physiological conditions in the presence of DAF/MCP) and on paroxysmal nocturnal hemoglobinuria erythrocytes (under low conductivity conditions in the absence of DAF/MCP).

Antigens, CD↗
PubMed1992

Factor I-dependent inactivation of human complement C4b of the classical pathway by C3b/C4b receptor (CR1, CD35) and membrane cofactor protein (MCP, CD46).

Proteolytic inactivation of C4b is a crucial step for regulation of the classical complement pathway. A plasma protease factor I and membrane cofactors, C3b/C4b receptor (CR1) and membrane cofactor protein (MCP), participate in the regulation of cell-bound C4b although the physiological potency of these cofactors remains unknown. We have examined the optimal conditions of the factor I-mediated C4b regulatory system using purified cofactors. CR1 being a cofactor at a cofactor/C4b ratio less than 0.1 (w/w), fluid phase C4b, and methylamine-treated C4 (C4ma) were degraded by factor I into C4bi: minimal Cd4 was generated in the fluid phase. Liposome-bound C4b (LAC4b), on the other hand, was degraded into C4c and C4d. CR1 showed two optimal pHs (6.0 and 7.5) for fluid phase C4b, but one (6.0) for LAC4b, and in both cases low conductivity conditions enhanced the C4bi generation. CR1 cofactor activity was barely influenced by the NP-40 concentration. On the other hand, MCP degraded C4b and C4ma, as a factor I-cofactor, more efficiently into C4c and C4d. Though MCP cofactor activity, like that of CR1, was enhanced under low conductivity conditions, it has only one optimal pH, 6.0, in both fluid and solid phases. Furthermore, as in the case of C3b cleavage, a sufficient NP-40 concentration to solubilize membrane was needed for MCP to express full cofactor activity for C4b, in contrast to CR1. MCP was less potent for C4b inactivation than for C3b inactivation, while CR1 acted as a slightly more effective cofactor for C4b cleavage than for C3b cleavage.(ABSTRACT TRUNCATED AT 250 WORDS)

Antigens, CD↗
PubMed1992

Levels of complement regulatory proteins, CD35 (CR1), CD46 (MCP) and CD55 (DAF) in human haematological malignancies.

Levels of the membrane complement regulatory proteins, C3b/C4b receptor (CR1, CD35), membrane cofactor protein (MCP, CD46), and decay-accelerating factor (DAF, CD55), expressed on cells from patients with haematological malignancies and normal subjects were assessed by flowcytometry using the respective monoclonal antibodies (mAbs). All myeloid and most lymphoid leukaemia samples tested were CR1-negative: two of the 42 leukaemia samples expressed minute amounts of CR1. Lack of CR1 in leukaemia cells was confirmed with two mAbs raised against CR1, 31R, and 243R, which recognized different epitopes and induced different degrees of CR1-mediated fluorescent shift on flow-cytometry in granulocytes and erythrocytes. MCP was increased in most chronic myelogenous leukaemia (CML) and chronic lymphocytic leukaemia (CLL), and was also increased in majority of acute nonlymphocytic leukaemia (ANLL), acute lymphocytic leukaemia (ALL) and non-Hodgkin's lymphoma (NHL). Levels of DAF were also high in CML and CLL, and were variable in other types of leukaemia: some were DAF-negative while others expressed extremely high levels of DAF. In CML patients, the high level of MCP and the lack of CR1 were normalized after medical treatment. These results are in agreement with the data obtained with human leukaemia cell lines, and support the hypothesis that CR1 is essentially a differentiated cell antigen and that a high level of MCP reflects some malignant transformation or an immature stage in blood cells.

Antibodies, Monoclonal↗
PubMed1992

Soluble forms of membrane cofactor protein (CD46, MCP) are present in plasma, tears, and seminal fluid in normal subjects.

We have established an ELISA for determination of membrane cofactor protein (MCP, CD46) both solubilized from cell membranes and released in body fluids. In this assay, mouse MoAbs against MCP, M177 and M160 whose epitopes were different, were used as capture and detection antibodies, respectively. The NP-40 concentration in samples for MCP to be measured must be less than 0.05%. The detection limit of this MCP assay was 0.5 ng. The assay was used to quantify solubilized membrane MCP, and soluble MCP in normal human plasma, serum, urine, saliva, tears, and seminal fluid, and culture media of tumour cell lines. Soluble MCP was barely detected in the conditioned media of the cell lines. The levels of sMCP in plasma and serum were 10-60 ng/ml and that in tears, 0-50 ng/ml. Seminal fluid contained about 10-fold more soluble MCP than serum. Soluble MCP was not detectable by this assay in the other body fluids, suggesting that their MCP levels were less than the detection limit, if any.

Anticoagulants↗
PubMed1991

A covalent dimer of complement C4b serves as a subunit of a novel C5 convertase that involves no C3 derivatives.

A C intermediate, LAC14, was prepared from TNP-aminocaproyl liposomes sensitized with anti-TNP antibody (Ab) and purified human C1 and C4. LAC14, containing radiolabeled C4, was analyzed by SDS-PAGE followed by autoradiography, and yielded a 210-kDa band and a predominant 400-kDa band. The 210-kDa band consisted of monomeric C4b bound to low molecular mass acceptors. The 400-kDa band was comprised of a 200-kDa moiety, as well as beta- and gamma-chains of C4. The 200-kDa moiety contained neither C1 nor sensitizing Ab, but it was largely decreased by treatment with NH2OH to the 90-kDa moiety with the mobility corresponding to the alpha'-chain of C4b. A covalent dimer of C4b, therefore, is the predominant form of C4b deposited on liposomes sensitized with antibody. The C4b-C4b dimer formed rapidly (within 5 min) followed by slow dissociation into monomers. The LAC14 bearing the C4b dimer but not the monomer was lysed, although with relatively low efficiency, by the addition of oxyC2 and EDTA-supplemented C3-deficient serum (C3DS), and, furthermore, LAC142 possessed the ability to convert C5 into C5a and C5b. Moreover, lysis was inhibited not by anti-C3 Ab but by anti-C4 Ab. In other experiments, the dimer served as an element of C3 convertase, as well. These findings imply that the C4b dimer, when complexed with C2, expresses C3/C5 convertase activity without participation of C3, and may provide a molecular mechanism whereby sera from patients with complete C3 deficiency retain the ability to induce C-mediated cytolysis.

Autoradiography↗
PubMed1991

Reconstitution of C5 convertase of the alternative complement pathway with isolated C3b dimer and factors B and D.

C5 convertase of the alternative complement pathway is a trimolecular complex consisting of two molecules of C3b and one molecule of Bb. We previously proposed a model of the alternative pathway C5 convertase in which the second C3b molecule binds covalently to the first C3b molecule bearing Bb, and the C5 molecule binds to each C3b molecule of the covalently linked C3b dimer, resulting in its appropriate presentation to the catalytic site on Bb. In the present study, we purified the covalently linked C3b dimer and reconstituted the C5 convertase with the C3b dimer and factors B and D to obtain evidence in support of this model. An insoluble glucan, OMZ-176, was incubated with human serum to activate the alternative pathway and to allow formation of the alternative C5 convertase on the surface of the glucan, and the glucan bearing the C5 convertase was then solubilized by incubation with glucosidases. In this way, the covalently linked C3b dimer was obtained in solution without using a detergent. The C3b dimer was then separated from enzymes, C3b monomer, C3b oligomer, and other materials by chromatographies. SDS-PAGE analysis demonstrated that the purified C3b dimer had intact alpha'-chains. Alternative pathway C5 convertase was reconstituted when the isolated C3b dimer was incubated with factors B and D. The presence of P enhanced C5 convertase formation threefold. These results support the notions that the formation of the covalently linked C3b dimer is a general phenomenon associated with activation of the alternative pathway and that the C3b dimer acts as a part of the C5 convertase.

Complement C3-C5 Convertases↗
PubMed1991

Alternative complement pathway-mediated myeloid cell cytotoxicity: repertoire of membrane factors participating in regulation of C3 deposition and cytolysis.

Most human nucleated cells and cell lines possess C3 step regulators, decay-accelerating factor (DAF; CD55) and membrane cofactor protein (MCP; CD46) and an inhibitor of membrane attack complex (MAC) formation (p18; CD59). Unless DAF and MCP were simultaneously blocked by their antibodies, Mg(2+)-EGTA-human serum treatment did not induce C3 deposition on most nucleated cells. Furthermore, less than 20% lysis occurred even after the block of all the three factors. In contrast, three myeloid cell lines, U-937, HL-60 and p39, were found to exhibit unusual C3 deposition or cytolysis. U-937 possessed DAF and MCP but lacked p18, and about 50% was lysed by treatment with anti-DAF and anti-MCP followed by Mg(2+)-EGTA-serum, which caused C3, C5 and C8 deposition. Anti-DAF evoked similar but less complement (C) deposition and cytolysis while anti-MCP alone did not, although it enhanced the anti-DAF-mediated C deposition and cytolysis. Thus, once the C3 step is overcome, U-937 is attacked by the late components leading to cytolysis because of the absence of p18. On the other hand, HL60 allowed the deposition of C3 by blocking of either DAF or MCP followed by the Mg(2+)-EGTA-serum treatment. C5, C8 and C9 were subsequently deposited but resulted in no lysis. Lysis of 60% was attained by the additional blocking of p18. Thus, HL60 is poorly protected by C3 and C9 step regulation. Strikingly, extensive C3 deposition occurs on p39 without any antibody treatment, suggestive of the presence of unique alternative pathway activators. However, little cytolysis was induced on p39 even by blocking of all three inhibitors with antibodies. These results suggest that in activation of the alternative pathway on myeloid cells, C3 step is controlled by the inhibitors and alternative pathway activators, and C-mediated cytolysis is blocked by p18 and additional regulatory mechanisms or factors which assist in protection of nucleated host cells from MAC attack. Susceptibility to homologous C of these cell lines, therefore, reflects relatively low potency of C regulation on their membrane.

Antigens, CD↗
PubMed1991

Preferential inactivation of the C5 convertase of the alternative complement pathway by factor I and membrane cofactor protein (MCP).

Human C3b bound to the ghost of sheep erythrocytes (E*) via activation of the alternative complement pathway (E*AC3b) consists of four major constituents on SDS-PAGE of 350, 260, 210 and 180 kDa. 350 kDa C3b is a dimeric form of C3b in which the alpha' chain of one C3b binds covalently to that of the other C3b. This complex is presumed to serve as a core for the alternative pathway C5 convertase. The other C3b populations are monomers complexed with membrane proteins or sugars. Using E*AC3b (C3b labeled) as a substrate, we have investigated functional properties of membrane cofactor protein (MCP), which is an integral membrane protein with C3b-binding and factor I-dependent cofactor activities. In conjunction with factor I, MCP was found to degrade the protein-bound C3b preferentially including the 350 kDa dimer. There was a similar but lesser tendency of this selective cleavage of C3b-dimer by CR1 but not by factor H or C4bp. In contrast to CR1 and factor H, detergent solubilization of EAC3b was required for MCP to fully express its cofactor activity for this selective degradation of C3b. We next separated the C3b dimer from the monomers and assessed their ability to assemble the alternative C5 convertase. The C3b dimer but not the monomers expressed C5 convertase activity following the addition of factors B and D, C5 and Ni2+. Kinetic analysis of the degradation of the C3b dimer by MCP and factor I suggested that only one C3b was efficiently converted to C3bi and this occurred concomitant with a decrease in C5 convertase activity. These results suggest that MCP has the ability to more efficiently interact with protein-bound C3b and that this may relate as well to its preferential ability to irreversibly inactivate the C5 convertase.

Antigens, CD↗
PubMed1991

Deficiency of complement decay-accelerating factor (DAF, CD55) in non-Hodgkin's lymphoma.

We have assessed levels of surface-expressed complement regulatory proteins, decay-accelerating factor (DAF) and membrane cofactor protein (MCP) on cells from patients with hematological malignancies. Neither malignant cells nor unaffected nucleated blood cells from the patients lacked MCP. On the other hand, complete deficiency of DAF was found in 2/10 of non-Hodgkin's lymphoma (NHL), while none of the 38 patients with acute nonlymphocytic leukemia (ANLL) (14 cases), chronic myelogenous leukemia (CML) (6 cases), acute lymphocytic leukemia (ALL) (12 cases) and chronic lymphocytic leukemia (CLL) (6 cases) lacked DAF. The two patients with DAF-negative NHL had no history of paroxysmal nocturnal hemoglobinuria (PNH), and their peripheral blood cells were DAF-positive. One DAF-negative NHL exhibited T cell markers and the other those of B cell. In both cases, treatment of the DAF-negative lymphoma cells with antibody against MCP (M177) followed by Mg(2+)-EGTA-serum resulted in efficient deposition of homologous C3. These results infer that some NHL specifically lack DAF and, through treatment with M177, are targeted by homologous C3.

Antibodies, Monoclonal↗
PubMed1991

Enhancement of lymphocyte-mediated K562 cytotoxicity by antibodies against complement membrane cofactor protein (CD46) and decay-accelerating factor (CD55).

A natural killer (NK) target, K562 (a human erythroblastoid cell line), was found by flow cytometry to express three complement regulatory membrane proteins on its surface: decay-accelerating factor (DAF, CD55), membrane cofactor protein (MCP, CD46) and p18 (CD59). We examined the effects of F(ab')2 of polyclonal antibodies raised against DAF and MCP and monoclonal antibody to p18 on the susceptibility of K562 to cytolysis by homologous lymphocytes, granulocytes and complement. C3bi-deposition was induced on K562 when the cells were treated with both anti-DAF and anti-MCP. Lymphocyte-mediated K562 cytolysis was markedly enhanced by these two antibodies whereas anti-p18 barely affected the degree of cytolysis. Complement immunocytolysis, on the other hand, became highest by combination treatment with the three antibodies, although anti-p18 and either anti-DAF or anti-MCP induced little potentiation of cytolysis. Granulocytes showed the least cytolysis and minimal potentiation of lysis by treatment with both anti-DAF and anti-MCP.

Antibodies, Monoclonal↗
PubMed1991

Expression and characterization of membrane co-factor protein (MCP) in human skin.

Membrane co-factor protein (MCP; CD46) is an integral membrane protein with molecular weight (MW) of the two species of 63 kD and 55 kD, and regulates autologous complement activation, with the activity of factor I cofactor. The quantity of each species is genetically regulated, and two codominantly inherited allelic variants account for the three phenotypic patterns. By immunohistochemical study, MCP was found both in the intercellular spaces of the epidermis and on the endothelial cells in the dermis of normal human skin in vivo. The intensity of the staining pattern was higher in the basal layer than in the granular layer. By Western blot analysis with use of a monoclonal antibody, MCP in the epidermis appeared as several bands ranged from 60-50 kD, with a major band of 56 kD, which was different from those in either polymorphonuclear cells, platelets, and cultured keratinocytes. No other variants were found in the epidermis obtained from skin of 20 normal humans. Complement activation in human skin may be regulated at several steps, including DAF and HRF20, thereby protecting cells from autologous complement attack.

Antigens, CD↗
PubMed1991

Granulocyte-dependent extracellular cytotoxicity is enhanced by complement C3bi and independent of phagocytosis.

We have evaluated phagocytosis, C3-binding and cytotoxicity of human leukocytes simultaneously, using IgM-sensitized C3-fragment-bearing sheep erythrocytes (EAC3b, EAC3bi) as targets. In this method, 51Cr-labelled EAC3b or EAC3bi were added to human peripheral granulocytes anchored by fibronectin onto microtitre plate wells. The degrees of haemolysis, binding and ingestion of the target cells were estimated from the radioactivity released. We found that the granulocytes predominantly lysed EAC3bi but not EAC3b or EAC4b. EAC3bi lysis elicited from granulocytes was as effective as that from lymphocytes under the same assay conditions. However, one difference in the cytolysis of the two effector cells was that EAC3bi bound efficiently to all of the granulocytes similarly to EAC3b, whereas it bound to only 4% of the lymphocytes. The bound cells did not appear to be efficiently phagocytosed by the granulocytes. Blocking studies using antibodies suggested that C3bi receptors, CR3 and CR4, but not other C3-binding proteins, C3b/C4b receptor (CR1), membrane cofactor protein (MCP) or decay-accelerating factor (DAF), are involved in granulocyte-mediated haemolysis. We speculate that simultaneous stimulation of the C3bi receptors and the fibronectin receptor results in elicitation of cytotoxicity by granulocytes.

Carrier Proteins↗
PubMed1991

[Cell-associated complement regulatory proteins and their relation to disease processes].

C3-deposition is a key step for activation of the complement system, which involves C9-mediated immunocytolysis, immunoadherence, C3 receptor-mediated phagocytosis, NK potentiation, anaphylatoxin release, and amplification of C3 activation. Foreign material is eliminated even in the preimmune stage by these complement functions. Self cells, on the other hand, must circumvent the C3-attack, so that they express complement regulatory proteins, namely C3b/C4b receptor (CR1, CD35), decay-accelerating factor (DAF, CD55), membrane cofactor protein (MCP, CD46). We herein review the properties of these regulatory proteins and discuss the relationships between disease processes and the aberrance of these regulatory proteins.

Antigens, CD↗
PubMed1991

Human complement regulatory proteins expressed on mouse A9 cells containing a human chromosome 1.

The structural genes of human complement regulatory proteins are clustered on chromosome 1 at position q3.2. Human chromosome 1 was transferred into a mouse fibroblast cell line, A9 [designated as A9(neo-1)], and the surface expression of its gene products participating in complement regulation, namely C3b/C4b receptor (CR1, CD35), decay-accelerating factor (DAF, CD55), membrane co-factor protein (MCP, CD46) and C3d/EB virus receptor (CR2, CD21), were assessed using respective monoclonal antibodies by flow cytometry. CR1 became positive within 7 days of culture. MCP appeared in a small population of cells by Day 3 and, together with DAF, began to increase on Day 7. CR2 appeared on Day 14. The order of the expression was CR1 greater than DAF = MCP greater than CR2. On Day 42, however, all became negative except for MCP, which was markedly diminished. These human regulatory proteins were specifically associated with the presence of human chromosome 1, since none of them were expressed on human chromosome 12-transferred A9 cells [A9(neo-12)]. Intact A9 and A9(neo-12) cells activated human complement via the alternative pathway. The activation of this pathway was suppressed in the A9(neo-1) cells that expressed CR1, DAF and MCP. Slight protective activity was still observed in the 42-day cultured A9(neo-1) cells expressing only trace MCP. These results suggest that human complement regulators, expressed via the transferred human chromosome 1, can protect heterologous cells from complement, overcoming their ability to activate the human alternative pathway.

Animals↗
PubMed1990

Complement-mediated tumor cell damage induced by antibodies against membrane cofactor protein (MCP, CD46).

We have developed polyclonal and monoclonal antibodies against human membrane cofactor protein (MCP) to use as tools to investigate the functions of MCP on intact nucleated cells. Two human T cell lines, CEM and TALL, are CR1- and DAF-. Pretreatment of these cell lines with M177 and polyclonal anti-MCP, which inhibit cofactor activity almost completely, resulted in effective C3 deposition immediately following addition of these cells to Mg2+/EGTA/human sera. The deposited C3 remained expressed partly on the cell surface and most of them were gradually converted to C3bi. Some of the deposited C3 were complexed with membrane proteins, since 140- and 250-kD bands became significantly accumulated on SDS-PAGE by treatment with the antibodies. We next tested whether these C3-coated cells were damaged by complement-mediated cytolysis. p18, an inhibitor of membrane attack complex (MAC) formation, was negative in TALL but positive in CEM. TALL was lysed efficiently only by treatment with the polyclonal anti-MCP, while CEM showed only slight lysis with the same treatment. Monoclonal antibodies to MCP, including M177, caused only minimal cell destruction. Based on these results, together with the fact that decay-accelerating factor (DAF) serves as a factor for preventing C3 attack on human cells, we conclude that MCP and DAF cooperatively protect host cells from C3 targeting and, in these T cell lines, MCP is sufficient for preventing C3 deposition even without DAF. After all, human cells undergo almost no autologous complement-mediated cytolysis if they express at least one of the functionally active inhibitors, MCP, DAF, or p18.

Animals↗
PubMed1990

Regulatory system of guinea-pig complement C3b: two factor I-cofactor proteins on guinea-pig peritoneal granulocytes.

Complement factor I is a plasma protease serving for proteolytic inactivation of C3b together with its cofactor. We have identified two factor I-cofactor activities in solubilized extracts of guinea-pig peritoneal granulocytes using guinea-pig factor I (Igp) and fluorescent-labeled methylamine-treated guinea-pig C3 (f-C3(MA)gp). One of these eluted from a chromatofocusing column between pH 7.6-7.1, and the other at about pH 5.7. These two cofactor fractions both interacted with Igp and, to a lesser degree, with human factor I (Ihu) on C3(MA)gp cleaving it into an inactive C3bi analogue, but did not cleave methylamine-treated human C3 (C3(MA)hu) together with Igp or Ihu. These factors are therefore species specific. The neutral and acidic fractions with cofactor activity contained C3(MA)gp-binding proteins with a doublet of 55 kDa and 42 kDa, and a singlet of 160 kDa, respectively, on SDS-PAGE. These proteins may be membrane cofactor protein (MCP) and C3b/C4b receptor (CR1) of guinea-pigs.

Animals↗