Analysis of the interactions between properdin, the third component of complement (C3), and its physiological activation products

The interactions of properdin with both surface-bound and fluid-phase C3 (the third component of complement) and its activation products have been investigated by using a purified preparation of the ‘native’ form. At physiological ionic strength, a weak interaction with cell-bound C3b (the larger activation fragment of C3) could be demonstrated. In the presence of Factor B this interaction was enhanced, and further enhancement was seen when C3bBb sites were formed on the erythrocytes. The avidities of properdin for cell-bound iC3b (the initial product of Factors I and H action on C3b) and C3b were compared at low ionic strength, with that measured for iC3b being less than that for C3b. In contrast, the affinities of properdin for fluid-phase C3b, iC3b and C3c (the larger product of Factors I and H or CR1 (the C3b receptor) action on iC3b) were all very similar, and apparently much weaker than that for cell-bound C3b. No interaction with either native C3 or, more surprisingly, C3i (haemolytically inactive C3) could be detected. Properdin also inhibited Factor I binding to, and action upon, cell-bound C3b, but did not inhibit Factor I action on fluid-phase C3b. These data permit a more detailed description of the roles of properdin in the alternative pathway of complement activation, emphasizing its importance in concentrating activation at the activating surface.

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The mechanism of action of the C3b inactivator (conglutinogen- activating factor) on its naturally occurring substrate, the major fragment of the third component of complement (C3b)

Journal of Experimental Medicine ◽

10.1084/jem.141.5.1221 ◽

1975 ◽

Vol 141 (5) ◽

pp. 1221-1226 ◽

Cited By ~ 46

Author(s):

JD Gitlin ◽

FS Rosen ◽

PJ Lachmann

Keyword(s):

Alternative Pathway ◽

Fluid Phase ◽

Complement C3 ◽

Classical Pathway ◽

Physiological Mechanisms ◽

The Third ◽

Immune Adherence ◽

Normal Human ◽

Molecular Nature ◽

Third Component Of Complement

The fixation of the third component of complement (C3) results in many important biological phenomenon, among which are (a) immune adherence (1), (b) enhancement of phagocytosis (2,3), (c) the release of an anaphylatoxin which is a potent releaser of histamine (4), and (d) the feedback activation of the alternative pathway (5,6). The physiological mechanisms involving C3 fixation require the generation of a C3 convertase which may occur by two separate pathways. C3 convertase can be generated, in the form of C42, by the so-called classical pathway of activation or in the form C3b,B by the alternative or properdin pathway (7). In both cases, C3 is converted to C3b by cleavage of a small peptide, C3a. Normal human serum contains an inactivator of activated C3b. This C2b inactivator or conglutinogen-activating factor (KAF) has been shown to inhibit both immune hemolysis and the immune adherence properties of C3b and to cause cleavage of C3b in the fixed and fluid- phase stages (8-11). Although it is known that the C3b inactivator is not depleted during its reaction with C3b and that C3b treated with the C3b inactivator becomes extremely sensitive to proteolytic digestion by trypsin and trypsin-like enzymes (9), the exact molecular nature of the action of the C3b inactivator on C3b has not been studied. In an effort to delineate the products of this interaction, purified C3b and C3b inactivator were allowed to react for various specific lengths of time and the products of these reactions were then analyzed.

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Binding of fluid-phase complement components C3 and C3b to human lymphocytes

Biochemical Journal ◽

10.1042/bj1980509 ◽

1981 ◽

Vol 198 (3) ◽

pp. 509-518 ◽

Cited By ~ 8

Author(s):

E Sim ◽

R B Sim

Keyword(s):

Human Lymphocytes ◽

Fluid Phase ◽

Complement C3 ◽

Human Tonsil ◽

Complement Components ◽

Sheep Erythrocytes ◽

The Third ◽

Complement Component C3 ◽

Specific Manner ◽

Third Component Of Complement

It is known that a population of B-lymphocytes has receptors for the third component of complement, C3, and that these lymphocytes may be identified by their ability to form rosettes with sheep erythrocytes coated with covalently bound fragments of complement component C3. Human tonsil lymphocytes, enriched for B-cells, form rosettes with sheep erythrocytes coated with antibody and complement components C1, C4b and C3b (EAC143b cells). Fluid-phase C3 will inhibit rosette formation between EAC143b and human tonsil lymphocytes over the same concentration range as fluid-phase C3b. C3 is not cleaved to C3b during incubation with lymphocytes or with lymphocytes and EAC143b cells. Fluid-phase 125I-labelled C3 and 125I-labelled C3b bind to lymphocytes in a specific manner. The characteristics of binding of both radioiodinated C3 and radioiodinated C3b are very similar, but the binding oc C3 is again not a result of cleavage to C3b. Salicylhydroxamic acid does not inhibit binding of 125I-labelled C3 to tonsil lymphocytes at concentrations that completely inhibit binding of 125I-labelled C3 to EAC142 cells via the nascent binding site of C3b. It is concluded that C3 and C3b share a common feature involved in binding to lymphocytes bearing receptors for the third component of complement.

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Effect of heparin on complement activation and lysis of paroxysmal nocturnal hemoglobinuria (PNH) red cells

Blood ◽

10.1182/blood.v50.2.239.239 ◽

1977 ◽

Vol 50 (2) ◽

pp. 239-247 ◽

Cited By ~ 25

Author(s):

GL Logue

Keyword(s):

Complement Activation ◽

Paroxysmal Nocturnal Hemoglobinuria ◽

Alternative Pathway ◽

Red Cells ◽

Complement C3 ◽

Red Cell ◽

The Third ◽

Biphasic Effect ◽

Third Component Of Complement

Abstract The effect of heparin upon the binding of the third component of complement (C3) to PNH red cells in vitro and their subsequent hemolysis is described. Heparin, in increasing concentrations, progressively inhibits membrane C3 fixation and hemolysis when the classic complement pathway is activated by anti-red cell antibodies. Heparin has a biphasic effect upon membrane C3 fixation and hemolysis when complement is activated in serum at decreased ionic strength (sucrose lysis) or in serum at decreased pH (Ham test). Heparin in concentrations above 2 U/ml inhibits C3 binding and hemolysis while lower concentrations of heparin enhance the consequences of complement activation by these two procedures. This enhanced complement activation may explain the increased hemolysis sometimes reported in PNH patients treated with heparin, and suggests that heparin may aggravate the consequences of pathologic alternative pathway complement activation in other diseases.

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Effect of heparin on complement activation and lysis of paroxysmal nocturnal hemoglobinuria (PNH) red cells

Blood ◽

10.1182/blood.v50.2.239.bloodjournal502239 ◽

1977 ◽

Vol 50 (2) ◽

pp. 239-247 ◽

Cited By ~ 1

Author(s):

GL Logue

Keyword(s):

Complement Activation ◽

Paroxysmal Nocturnal Hemoglobinuria ◽

Alternative Pathway ◽

Red Cells ◽

Complement C3 ◽

Red Cell ◽

The Third ◽

Biphasic Effect ◽

Third Component Of Complement

The effect of heparin upon the binding of the third component of complement (C3) to PNH red cells in vitro and their subsequent hemolysis is described. Heparin, in increasing concentrations, progressively inhibits membrane C3 fixation and hemolysis when the classic complement pathway is activated by anti-red cell antibodies. Heparin has a biphasic effect upon membrane C3 fixation and hemolysis when complement is activated in serum at decreased ionic strength (sucrose lysis) or in serum at decreased pH (Ham test). Heparin in concentrations above 2 U/ml inhibits C3 binding and hemolysis while lower concentrations of heparin enhance the consequences of complement activation by these two procedures. This enhanced complement activation may explain the increased hemolysis sometimes reported in PNH patients treated with heparin, and suggests that heparin may aggravate the consequences of pathologic alternative pathway complement activation in other diseases.

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C3a and C3b Activation Products of the Third Component of Complement (C3) Are Critical for Normal Liver Recovery after Toxic Injury

The Journal of Immunology ◽

10.4049/jimmunol.173.2.747 ◽

2004 ◽

Vol 173 (2) ◽

pp. 747-754 ◽

Cited By ~ 108

Author(s):

Maciej M. Markiewski ◽

Dimitrios Mastellos ◽

Ruxandra Tudoran ◽

Robert A. DeAngelis ◽

Christoph W. Strey ◽

...

Keyword(s):

Normal Liver ◽

Complement C3 ◽

The Third ◽

Toxic Injury ◽

Activation Products ◽

Third Component Of Complement

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New functional and structural insights from updated mutational databases for complement factor H, Factor I, membrane cofactor protein and C3

Bioscience Reports ◽

10.1042/bsr20140117 ◽

2014 ◽

Vol 34 (5) ◽

Cited By ~ 41

Author(s):

Elizabeth Rodriguez ◽

Pavithra M. Rallapalli ◽

Amy J. Osborne ◽

Stephen J. Perkins

Keyword(s):

Alternative Pathway ◽

Factor H ◽

Complement Factor H ◽

Complement C3 ◽

Complement Factor ◽

Membrane Cofactor Protein ◽

Complement Alternative Pathway ◽

Factor I ◽

Mutational Hotspots ◽

Structural Insights

A new compilation of 324 mutations in four major proteins from the complement alternative pathway reveals mutational hotspots in factor H and complement C3, and less so in factor I and membrane cofactor protein. Their associations with function are discussed.

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