https://www.cell.com/cell/pdf/0092-8674(84)90039-4.pdf

An alternative pathway of T-cell activation: A functional role for the 50 kd T11 sheep erythrocyte receptor protein

https://science.sciencemag.org/content/sci/120/3112/279.full.pdf

The Properdin System and Immunity: I. Demonstration and Isolation of a New Serum Protein, Properdin, and Its Role in Immune Phenomena

https://www.amjmed.com/article/0002-9343(63)90162-1/pdf

A biochemical abnormality in herediatry angioneurotic edema: absence of serum inhibitor of c' 1-esterase.

Evidence has accumulated indicating the existence of a second complement activation mechanism which is functionally analogous to C1, C2, and C4. The noncomplement protein C3PA, previously recognized through its ability to form a complex enzyme with a protein from cobra venom, appears to be the precursor of the C4,2 analogue. It is a thermolabile β-globulin with a molecular weight of 80,000. When serum is treated with naturally occurring plant or bacterial polysaccharides, the C3PA is cleaved into at least two fragments, one having the electrophoretic mobility of a γ-globulin and a molecular weight of 60,000, and the other being an acidic peptide with a molecular weight of 20,000. The larger fragment has the ability to cleave C3 into C3a and C3b and is therefore called C3 activator. It arises from the action of an as yet unidentified serum enzyme upon the C3PA, which is tentatively called C3PA convertase. In addition to endotoxins, yeast cell walls, inulin, and agar, aggregates of immunoglobulins were found to be activating substances, including human IgA, guinea pig γ1, and duck antibody. Serum depleted of C3PA had reduced E. coli bactericidal and increased hemolytic activity. The relationship of the C3-activator system to experimental and clinical observations has been discussed.

https://rupress.org/jem/article-pdf/134/3/90/1415898/90s.pdf

The c3-activator system: an alternate pathway of complement activation

The effects of bacterial endotoxins on host mediation systems. A review

A detailed method for the zymosan assay of properdin is described, together with procedures for the preparation and standardization of reagents employed in the test. The reliability and reproducibility of the assay, as well as its limitations, are discussed.

https://rupress.org/jem/article-pdf/103/1/1/1078652/1.pdf

The properdin system and immunity iii. the zymosan assay of properdin

https://science.sciencemag.org/content/sci/122/3169/545.full.pdf

Properdin System and Immunity: II. Interaction of the Properdin System with Polysaccharides

Human complement is inactivated by plasmin, the proteolytic enzyme of plasma or serum active at or near neutrality.

The addition of streptokinase to human serum, which converts plasminogen to plasmin, also causes the inactivation of complement components C'2 and C'4 and varying amounts of C'1. C'3 is the most resistant to inactivation by plasmin. Chloroform-activated human plasmin and bovine plasmin also destroy these components of complement, but are less effective than the streptokinase-activated enzyme. The inactivation of complement by the addition of streptokinase to human serum is inhibited by high hydrogen ion concentrations, low temperature, and elevated ionic strength. The inactivation of the components of complement in various fractions of serum is influenced by the available plasminogen and the content of plasmin inhibitors in these fractions.

Certain similarities are pointed out between the components of complement and the factors in the plasmin system and between the inactivation of the components of complement by antigen-antibody reactions, by specific agents, and by plasmin.

The possible significance of these relationships in immune hemolysis and complement fixation, and the possible role of the plasmin system in the instability of complement and the development of anticomplementary properties in serum are discussed.

/pdf/the-inactivation-of-complement-and-its-components-by-plasmin-1a5vonjqyk.pdf

The inactivation of complement and its components by plasmin

Summary Mg ++ is required for the inactivation of C′3 by insoluble residues of yeast cells (zymosan). The concentration of Mg ++ in normal serum is more than adequate for the reaction to proceed optimally. The requirement for Mg ++ is also demonstrated by the greater uptake of serum nitrogen by zymosan in the presence of Mg ++ than in its absence. The inactivation of human C′3 by zymosan appears to be a stoichiometric reaction sharply dependent on temperature, ionic strength and pH. The optimum conditions are at 37 C, ionic strength 0.15 or less, and pH 6.8–8.6. The complex formed upon the addition of zymosan to serum is highly undissociable or results in the destruction of C′3 activity. Attempts to elute C′3 from the zymosan complex were unsuccessful.

Livia Blum

Papers

The Properdin System and Immunity: I. Demonstration and Isolation of a New Serum Protein, Properdin, and Its Role in Immune Phenomena

The properdin system and immunity iii. the zymosan assay of properdin

Properdin System and Immunity: II. Interaction of the Properdin System with Polysaccharides

The inactivation of complement and its components by plasmin

The Requirement for Magnesium Ions in the Inactivation of the Third Component of Human Complement (C′3) by Insoluble Residues of Yeast Cells (Zymosan)